xz: Move sandboxing code to sandbox.c and improve Landlock sandbox.
Landlock is now always used just like pledge(2) is: first in more permissive mode and later (under certain common conditions) in a strict mode that doesn't allow opening more files. I put pledge(2) first in sandbox.c because it's the simplest API to use and still somewhat fine-grained for basic applications. So it's the simplest thing to understand for anyone reading sandbox.c.
This commit is contained in:
Lasse Collin
parent
7312dfbb02
commit
374868d81d
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@ -1393,6 +1393,8 @@ if(NOT MSVC OR MSVC_VERSION GREATER_EQUAL 1900)
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src/xz/options.c
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src/xz/options.h
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src/xz/private.h
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src/xz/sandbox.c
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src/xz/sandbox.h
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src/xz/signals.c
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src/xz/signals.h
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src/xz/suffix.c
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@ -21,6 +21,8 @@ xz_SOURCES = \
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options.c \
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options.h \
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private.h \
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sandbox.c \
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sandbox.h \
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signals.c \
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signals.h \
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suffix.c \
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170
src/xz/file_io.c
170
src/xz/file_io.c
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@ -28,15 +28,6 @@ static bool warn_fchown;
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# include <utime.h>
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#endif
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#ifdef HAVE_CAP_RIGHTS_LIMIT
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# include <sys/capsicum.h>
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#endif
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#ifdef HAVE_LINUX_LANDLOCK_H
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# include <linux/landlock.h>
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# include <sys/syscall.h>
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#endif
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#include "tuklib_open_stdxxx.h"
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#ifdef _MSC_VER
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@ -92,11 +83,6 @@ typedef enum {
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/// If true, try to create sparse files when decompressing.
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static bool try_sparse = true;
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#ifdef ENABLE_SANDBOX
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/// True if the conditions for sandboxing (described in main()) have been met.
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static bool sandbox_allowed = false;
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#endif
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#ifndef TUKLIB_DOSLIKE
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/// File status flags of standard input. This is used by io_open_src()
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/// and io_close_src().
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@ -181,159 +167,6 @@ io_no_sparse(void)
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}
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#ifdef ENABLE_SANDBOX
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extern void
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io_allow_sandbox(void)
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{
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sandbox_allowed = true;
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return;
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}
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/// Enables operating-system-specific sandbox if it is possible.
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/// src_fd is the file descriptor of the input file.
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static void
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io_sandbox_enter(int src_fd)
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{
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if (!sandbox_allowed) {
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// This message is more often annoying than useful so
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// it's commented out. It can be useful when developing
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// the sandboxing code.
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//message(V_DEBUG, _("Sandbox is disabled due "
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// "to incompatible command line arguments"));
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return;
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}
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const char dummy_str[] = "x";
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// Try to ensure that both libc and xz locale files have been
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// loaded when NLS is enabled.
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snprintf(NULL, 0, "%s%s", _(dummy_str), strerror(EINVAL));
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// Try to ensure that iconv data files needed for handling multibyte
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// characters have been loaded. This is needed at least with glibc.
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tuklib_mbstr_width(dummy_str, NULL);
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#ifdef HAVE_CAP_RIGHTS_LIMIT
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// Capsicum needs FreeBSD 10.2 or later.
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cap_rights_t rights;
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if (cap_enter())
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goto error;
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if (cap_rights_limit(src_fd, cap_rights_init(&rights,
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CAP_EVENT, CAP_FCNTL, CAP_LOOKUP, CAP_READ, CAP_SEEK)))
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goto error;
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// If not reading from stdin, remove all capabilities from it.
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if (src_fd != STDIN_FILENO && cap_rights_limit(
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STDIN_FILENO, cap_rights_clear(&rights)))
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goto error;
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if (cap_rights_limit(STDOUT_FILENO, cap_rights_init(&rights,
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CAP_EVENT, CAP_FCNTL, CAP_FSTAT, CAP_LOOKUP,
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CAP_WRITE, CAP_SEEK)))
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goto error;
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if (cap_rights_limit(STDERR_FILENO, cap_rights_init(&rights,
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CAP_WRITE)))
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goto error;
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if (cap_rights_limit(user_abort_pipe[0], cap_rights_init(&rights,
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CAP_EVENT)))
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goto error;
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if (cap_rights_limit(user_abort_pipe[1], cap_rights_init(&rights,
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CAP_WRITE)))
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goto error;
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#elif defined(HAVE_PLEDGE)
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// pledge() was introduced in OpenBSD 5.9.
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//
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// main() unconditionally calls pledge() with fairly relaxed
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// promises which work in all situations. Here we make the
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// sandbox more strict.
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if (pledge("stdio", ""))
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goto error;
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(void)src_fd;
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#elif defined(HAVE_LINUX_LANDLOCK_H)
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int landlock_abi = syscall(SYS_landlock_create_ruleset,
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(void *)NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
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if (landlock_abi > 0) {
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// We support ABI versions 1-3.
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if (landlock_abi > 3)
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landlock_abi = 3;
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// We want to set all supported flags in handled_access_fs.
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// This way the ruleset will initially forbid access to all
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// actions that the available Landlock ABI version supports.
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// Exceptions can be added using landlock_add_rule(2) to
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// allow certain actions on certain files or directories.
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//
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// The same flag values are used on all archs. ABI v2 and v3
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// both add one new flag.
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//
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// First in ABI v1: LANDLOCK_ACCESS_FS_EXECUTE = 1ULL << 0
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// Last in ABI v1: LANDLOCK_ACCESS_FS_MAKE_SYM = 1ULL << 12
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// Last in ABI v2: LANDLOCK_ACCESS_FS_REFER = 1ULL << 13
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// Last in ABI v3: LANDLOCK_ACCESS_FS_TRUNCATE = 1ULL << 14
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//
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// This makes it simple to set the mask based on the ABI
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// version and we don't need to care which flags are #defined
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// in the installed <linux/landlock.h>.
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const struct landlock_ruleset_attr attr = {
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.handled_access_fs = (1ULL << (12 + landlock_abi)) - 1
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};
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const int ruleset_fd = syscall(SYS_landlock_create_ruleset,
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&attr, sizeof(attr), 0U);
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if (ruleset_fd < 0)
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goto error;
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// All files we need should have already been opened. Thus,
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// we don't need to add any rules using landlock_add_rule(2)
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// before activating the sandbox.
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//
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// NOTE: It's possible that the hack at the beginning of this
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// function isn't be good enough. It tries to get translations
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// and libc-specific files loaded but if it's not good enough
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// then perhaps a Landlock rule to allow reading from /usr
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// and/or the xz installation prefix would be needed.
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//
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// prctl(PR_SET_NO_NEW_PRIVS, ...) was already called in
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// main() so we don't do it here again.
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if (syscall(SYS_landlock_restrict_self, ruleset_fd, 0U) != 0)
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goto error;
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}
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(void)src_fd;
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#else
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# error ENABLE_SANDBOX is defined but no sandboxing method was found.
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#endif
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// This message is annoying in xz -lvv.
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//message(V_DEBUG, _("Sandbox was successfully enabled"));
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return;
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error:
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#ifdef HAVE_CAP_RIGHTS_LIMIT
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// If a kernel is configured without capability mode support or
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// used in an emulator that does not implement the capability
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// system calls, then the Capsicum system calls will fail and set
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// errno to ENOSYS. In that case xz will silently run without
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// the sandbox.
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if (errno == ENOSYS)
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return;
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#endif
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message_fatal(_("Failed to enable the sandbox"));
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}
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#endif // ENABLE_SANDBOX
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#ifndef TUKLIB_DOSLIKE
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/// \brief Waits for input or output to become available or for a signal
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///
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@ -889,7 +722,8 @@ io_open_src(const char *src_name)
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#ifdef ENABLE_SANDBOX
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if (!error)
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io_sandbox_enter(pair.src_fd);
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sandbox_enable_strict_if_allowed(pair.src_fd,
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user_abort_pipe[0], user_abort_pipe[1]);
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#endif
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return error ? NULL : &pair;
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@ -99,12 +99,6 @@ extern void io_write_to_user_abort_pipe(void);
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extern void io_no_sparse(void);
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#ifdef ENABLE_SANDBOX
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/// \brief main() calls this if conditions for sandboxing have been met.
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extern void io_allow_sandbox(void);
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#endif
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/// \brief Open the source file
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extern file_pair *io_open_src(const char *src_name);
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@ -12,12 +12,6 @@
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#include "private.h"
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#include <ctype.h>
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// prctl(PR_SET_NO_NEW_PRIVS, ...) is required with Landlock but it can be
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// activated even when conditions for strict sandboxing aren't met.
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#ifdef HAVE_LINUX_LANDLOCK_H
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# include <sys/prctl.h>
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#endif
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/// Exit status to use. This can be changed with set_exit_status().
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static enum exit_status_type exit_status = E_SUCCESS;
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@ -148,32 +142,6 @@ read_name(const args_info *args)
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int
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main(int argc, char **argv)
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{
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#ifdef HAVE_PLEDGE
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// OpenBSD's pledge(2) sandbox
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//
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// Unconditionally enable sandboxing with fairly relaxed promises.
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// This is still way better than having no sandbox at all. :-)
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// More strict promises will be made later in file_io.c if possible.
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if (pledge("stdio rpath wpath cpath fattr", "")) {
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// Don't translate the string or use message_fatal() as
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// those haven't been initialized yet.
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fprintf(stderr, "%s: Failed to enable the sandbox\n", argv[0]);
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return E_ERROR;
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}
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#endif
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#ifdef HAVE_LINUX_LANDLOCK_H
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// Prevent the process from gaining new privileges. This must be done
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// before landlock_restrict_self(2) in file_io.c but since we will
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// never need new privileges, this call can be done here already.
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//
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// This is supported since Linux 3.5. Ignore the return value to
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// keep compatibility with old kernels. landlock_restrict_self(2)
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// will fail if the no_new_privs attribute isn't set, thus if prctl()
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// fails here the error will still be detected when it matters.
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(void)prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
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#endif
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#if defined(_WIN32) && !defined(__CYGWIN__)
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InitializeCriticalSection(&exit_status_cs);
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#endif
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@ -187,6 +155,20 @@ main(int argc, char **argv)
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// even indirectly like locale and gettext initializations.
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io_init();
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#ifdef ENABLE_SANDBOX
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// Enable such sandboxing that can always be enabled.
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// This requires that progname has been set up.
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// It's also good that io_init() has been called because it
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// might need to do things that the initial sandbox won't allow.
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// Otherwise this should be called as early as possible.
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//
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// NOTE: Calling this before tuklib_gettext_init() means that
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// translated error message won't be available if sandbox
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// initialization fails. However, sandbox_init() shouldn't
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// fail and this order simply feels better.
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sandbox_init();
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#endif
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// Set up the locale and message translations.
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tuklib_gettext_init(PACKAGE, LOCALEDIR);
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@ -241,7 +223,7 @@ main(int argc, char **argv)
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signals_init();
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#ifdef ENABLE_SANDBOX
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// Set a flag that sandboxing is allowed if all these are true:
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// Set a flag that strict sandboxing is allowed if all these are true:
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// - --files or --files0 wasn't used.
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// - There is exactly one input file or we are reading from stdin.
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// - We won't create any files: output goes to stdout or --test
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@ -255,7 +237,7 @@ main(int argc, char **argv)
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if (args.files_name == NULL && args.arg_count == 1
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&& (opt_stdout || strcmp("-", args.arg_names[0]) == 0
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|| opt_mode == MODE_LIST))
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io_allow_sandbox();
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sandbox_allow_strict();
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#endif
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// coder_run() handles compression, decompression, and testing.
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@ -51,11 +51,6 @@
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# define STDERR_FILENO (fileno(stderr))
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#endif
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#if defined(HAVE_CAP_RIGHTS_LIMIT) || defined(HAVE_PLEDGE) \
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|| defined(HAVE_LINUX_LANDLOCK_H)
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# define ENABLE_SANDBOX 1
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#endif
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// Handling SIGTSTP keeps time-keeping for progress indicator correct
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// if xz is stopped. It requires use of clock_gettime() as that is
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// async-signal safe in POSIX. Require also SIGALRM support since
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@ -75,6 +70,7 @@
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#include "hardware.h"
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#include "file_io.h"
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#include "options.h"
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#include "sandbox.h"
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#include "signals.h"
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#include "suffix.h"
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#include "util.h"
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@ -0,0 +1,295 @@
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// SPDX-License-Identifier: 0BSD
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///////////////////////////////////////////////////////////////////////////////
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//
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/// \file sandbox.c
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/// \brief Sandbox support
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//
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// Author: Lasse Collin
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//
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///////////////////////////////////////////////////////////////////////////////
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#include "private.h"
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#ifndef ENABLE_SANDBOX
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// Prevent an empty translation unit when no sandboxing is supported.
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typedef int dummy;
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#else
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/// If the conditions for strict sandboxing (described in main())
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/// have been met, sandbox_allow_strict() can be called to set this
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/// variable to true.
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static bool strict_sandbox_allowed = false;
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extern void
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sandbox_allow_strict(void)
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{
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strict_sandbox_allowed = true;
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return;
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}
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// Strict sandboxing prevents opening any files. This *tries* to ensure
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// that any auxiliary files that might be required are already open.
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//
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// Returns true if strict sandboxing is allowed, false otherwise.
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static bool
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prepare_for_strict_sandbox(void)
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{
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if (!strict_sandbox_allowed)
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return false;
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const char dummy_str[] = "x";
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// Try to ensure that both libc and xz locale files have been
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// loaded when NLS is enabled.
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snprintf(NULL, 0, "%s%s", _(dummy_str), strerror(EINVAL));
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// Try to ensure that iconv data files needed for handling multibyte
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// characters have been loaded. This is needed at least with glibc.
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tuklib_mbstr_width(dummy_str, NULL);
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return true;
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}
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#endif
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#if defined(HAVE_PLEDGE)
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///////////////
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// pledge(2) //
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///////////////
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#include <unistd.h>
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extern void
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sandbox_init(void)
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{
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if (pledge("stdio rpath wpath cpath fattr", "")) {
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// gettext hasn't been initialized yet so
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// there's no point to call it here.
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message_fatal("Failed to enable the sandbox");
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}
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return;
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}
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extern void
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sandbox_enable_strict_if_allowed(int src_fd lzma_attribute((__unused__)),
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int pipe_event_fd lzma_attribute((__unused__)),
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int pipe_write_fd lzma_attribute((__unused__)))
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{
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if (!prepare_for_strict_sandbox())
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return;
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if (pledge("stdio", ""))
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message_fatal(_("Failed to enable the sandbox"));
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return;
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}
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||||
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#elif defined(HAVE_LINUX_LANDLOCK_H)
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//////////////
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// Landlock //
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//////////////
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#include <linux/landlock.h>
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#include <sys/syscall.h>
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#include <sys/prctl.h>
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// Highest Landlock ABI version supported by this file
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#define LANDLOCK_ABI_MAX 3
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|
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/// Landlock ABI version supported by the kernel
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static int landlock_abi;
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// The required_rights should have those bits set that must not be restricted.
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// This function will then bitwise-and ~required_rights with a mask matching
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// the Landlock ABI version, leaving only those bits set that are supported
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// by the ABI and allowed to be restricted by the function argument.
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static void
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enable_landlock(uint64_t required_rights)
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{
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assert(landlock_abi <= LANDLOCK_ABI_MAX);
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|
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if (landlock_abi <= 0)
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return;
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||||
|
||||
// We want to set all supported flags in handled_access_fs.
|
||||
// This way the ruleset will initially forbid access to all
|
||||
// actions that the available Landlock ABI version supports.
|
||||
// Exceptions can be added using landlock_add_rule(2) to
|
||||
// allow certain actions on certain files or directories.
|
||||
//
|
||||
// The same flag values are used on all archs. ABI v2 and v3
|
||||
// both add one new flag.
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||||
//
|
||||
// First in ABI v1: LANDLOCK_ACCESS_FS_EXECUTE = 1ULL << 0
|
||||
// Last in ABI v1: LANDLOCK_ACCESS_FS_MAKE_SYM = 1ULL << 12
|
||||
// Last in ABI v2: LANDLOCK_ACCESS_FS_REFER = 1ULL << 13
|
||||
// Last in ABI v3: LANDLOCK_ACCESS_FS_TRUNCATE = 1ULL << 14
|
||||
//
|
||||
// This makes it simple to set the mask based on the ABI
|
||||
// version and we don't need to care which flags are #defined
|
||||
// in the installed <linux/landlock.h>.
|
||||
const struct landlock_ruleset_attr attr = {
|
||||
.handled_access_fs = ((1ULL << (12 + landlock_abi)) - 1)
|
||||
& ~required_rights,
|
||||
};
|
||||
|
||||
const int ruleset_fd = syscall(SYS_landlock_create_ruleset,
|
||||
&attr, sizeof(attr), 0U);
|
||||
if (ruleset_fd < 0)
|
||||
message_fatal(_("Failed to enable the sandbox"));
|
||||
|
||||
// All files we need should have already been opened. Thus,
|
||||
// we don't need to add any rules using landlock_add_rule(2)
|
||||
// before activating the sandbox.
|
||||
//
|
||||
// NOTE: It's possible that the hack prepare_for_strict_sandbox()
|
||||
// isn't be good enough. It tries to get translations and
|
||||
// libc-specific files loaded but if it's not good enough
|
||||
// then perhaps a Landlock rule to allow reading from /usr
|
||||
// and/or the xz installation prefix would be needed.
|
||||
//
|
||||
// prctl(PR_SET_NO_NEW_PRIVS, ...) was already called in
|
||||
// sandbox_init() so we don't do it here again.
|
||||
if (syscall(SYS_landlock_restrict_self, ruleset_fd, 0U) != 0)
|
||||
message_fatal(_("Failed to enable the sandbox"));
|
||||
|
||||
return;
|
||||
}
|
||||
|
||||
|
||||
extern void
|
||||
sandbox_init(void)
|
||||
{
|
||||
// Prevent the process from gaining new privileges. This must be done
|
||||
// before landlock_restrict_self(2) but since we will never need new
|
||||
// privileges, this call can be done here already.
|
||||
//
|
||||
// This is supported since Linux 3.5. Ignore the return value to
|
||||
// keep compatibility with old kernels. landlock_restrict_self(2)
|
||||
// will fail if the no_new_privs attribute isn't set, thus if prctl()
|
||||
// fails here the error will still be detected when it matters.
|
||||
(void)prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
|
||||
|
||||
// Get the highest Landlock ABI version supported by the kernel.
|
||||
landlock_abi = syscall(SYS_landlock_create_ruleset,
|
||||
(void *)NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
|
||||
|
||||
// The kernel might support a newer ABI than this file.
|
||||
if (landlock_abi > LANDLOCK_ABI_MAX)
|
||||
landlock_abi = LANDLOCK_ABI_MAX;
|
||||
|
||||
// These are all in ABI version 1 already. We don't need truncate
|
||||
// rights because files are created with open() using O_EXCL and
|
||||
// without O_TRUNC.
|
||||
const uint64_t required_rights
|
||||
= LANDLOCK_ACCESS_FS_WRITE_FILE
|
||||
| LANDLOCK_ACCESS_FS_READ_FILE
|
||||
| LANDLOCK_ACCESS_FS_REMOVE_FILE
|
||||
| LANDLOCK_ACCESS_FS_MAKE_REG;
|
||||
|
||||
enable_landlock(required_rights);
|
||||
return;
|
||||
}
|
||||
|
||||
|
||||
extern void
|
||||
sandbox_enable_strict_if_allowed(int src_fd lzma_attribute((__unused__)),
|
||||
int pipe_event_fd lzma_attribute((__unused__)),
|
||||
int pipe_write_fd lzma_attribute((__unused__)))
|
||||
{
|
||||
if (!prepare_for_strict_sandbox())
|
||||
return;
|
||||
|
||||
// Allow all restrictions that the kernel supports with the
|
||||
// highest Landlock ABI version that the kernel or xz supports.
|
||||
enable_landlock(0);
|
||||
return;
|
||||
}
|
||||
|
||||
|
||||
#elif defined(HAVE_CAP_RIGHTS_LIMIT)
|
||||
|
||||
//////////////
|
||||
// Capsicum //
|
||||
//////////////
|
||||
|
||||
#include <sys/capsicum.h>
|
||||
|
||||
|
||||
extern void
|
||||
sandbox_init(void)
|
||||
{
|
||||
// Nothing to do.
|
||||
return;
|
||||
}
|
||||
|
||||
|
||||
extern void
|
||||
sandbox_enable_strict_if_allowed(
|
||||
int src_fd, int pipe_event_fd, int pipe_write_fd)
|
||||
{
|
||||
if (!prepare_for_strict_sandbox())
|
||||
return;
|
||||
|
||||
// Capsicum needs FreeBSD 10.2 or later.
|
||||
cap_rights_t rights;
|
||||
|
||||
if (cap_enter())
|
||||
goto error;
|
||||
|
||||
if (cap_rights_limit(src_fd, cap_rights_init(&rights,
|
||||
CAP_EVENT, CAP_FCNTL, CAP_LOOKUP, CAP_READ, CAP_SEEK)))
|
||||
goto error;
|
||||
|
||||
// If not reading from stdin, remove all capabilities from it.
|
||||
if (src_fd != STDIN_FILENO && cap_rights_limit(
|
||||
STDIN_FILENO, cap_rights_clear(&rights)))
|
||||
goto error;
|
||||
|
||||
if (cap_rights_limit(STDOUT_FILENO, cap_rights_init(&rights,
|
||||
CAP_EVENT, CAP_FCNTL, CAP_FSTAT, CAP_LOOKUP,
|
||||
CAP_WRITE, CAP_SEEK)))
|
||||
goto error;
|
||||
|
||||
if (cap_rights_limit(STDERR_FILENO, cap_rights_init(&rights,
|
||||
CAP_WRITE)))
|
||||
goto error;
|
||||
|
||||
if (cap_rights_limit(user_abort_pipe[0], cap_rights_init(&rights,
|
||||
CAP_EVENT)))
|
||||
goto error;
|
||||
|
||||
if (cap_rights_limit(user_abort_pipe[1], cap_rights_init(&rights,
|
||||
CAP_WRITE)))
|
||||
goto error;
|
||||
|
||||
return;
|
||||
|
||||
error:
|
||||
// If a kernel is configured without capability mode support or
|
||||
// used in an emulator that does not implement the capability
|
||||
// system calls, then the Capsicum system calls will fail and set
|
||||
// errno to ENOSYS. In that case xz will silently run without
|
||||
// the sandbox.
|
||||
if (errno == ENOSYS)
|
||||
return;
|
||||
|
||||
message_fatal(_("Failed to enable the sandbox"));
|
||||
}
|
||||
|
||||
#endif
|
||||
|
|
@ -0,0 +1,39 @@
|
|||
// SPDX-License-Identifier: 0BSD
|
||||
|
||||
///////////////////////////////////////////////////////////////////////////////
|
||||
//
|
||||
/// \file sandbox.h
|
||||
/// \brief Sandbox support
|
||||
//
|
||||
// Author: Lasse Collin
|
||||
//
|
||||
///////////////////////////////////////////////////////////////////////////////
|
||||
|
||||
#if defined(HAVE_PLEDGE) || defined(HAVE_LINUX_LANDLOCK_H) \
|
||||
|| defined(HAVE_CAP_RIGHTS_LIMIT)
|
||||
# define ENABLE_SANDBOX 1
|
||||
#endif
|
||||
|
||||
|
||||
/// \brief Enables early sandboxing that can always be enabled
|
||||
///
|
||||
/// This requires that tuklib_progname() and io_init() have been called.
|
||||
extern void sandbox_init(void);
|
||||
|
||||
|
||||
/// \brief Tell sandboxing code that strict sandboxing can be used
|
||||
///
|
||||
/// This function only sets a flag which will be read by
|
||||
/// sandbox_enable_strict_if_allowed().
|
||||
extern void sandbox_allow_strict(void);
|
||||
|
||||
|
||||
/// \brief Enable sandboxing that allows reading from one file
|
||||
///
|
||||
/// This does nothing if sandbox_allow_strict() hasn't been called.
|
||||
///
|
||||
/// \param src_fd File descriptor open for reading
|
||||
/// \param pipe_event_fd user_abort_pipe[0] from file_io.c
|
||||
/// \param pipe_write_fd user_abort_pipe[1] from file_io.c
|
||||
extern void sandbox_enable_strict_if_allowed(
|
||||
int src_fd, int pipe_event_fd, int pipe_write_fd);
|
||||
Loading…
Reference in New Issue