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xz: Support basic sandboxing with Linux Landlock (ABI versions 1-3).
It is enabled only when decompressing one file to stdout, similar to how Capsicum is used. Landlock was added in Linux 5.13.
This commit is contained in:
Lasse Collin
parent
3a1e9fd031
commit
8276c7f41c
5 changed files with 98 additions and 5 deletions
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@ -1246,7 +1246,8 @@ if(NOT MSVC OR MSVC_VERSION GREATER_EQUAL 1900)
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# OFF Disable sandboxing.
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# capsicum Require Capsicum (FreeBSD >= 10.2) and fail if not found.
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# pledge Require pledge(2) (OpenBSD >= 5.9) and fail if not found.
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set(SUPPORTED_SANDBOX_METHODS ON OFF capsicum pledge)
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# landlock Require Landlock (Linux >= 5.13) and fail if not found.
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set(SUPPORTED_SANDBOX_METHODS ON OFF capsicum pledge landlock)
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set(ENABLE_SANDBOX ON CACHE STRING "Sandboxing method to use in 'xz'")
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@ -1285,6 +1286,15 @@ if(NOT MSVC OR MSVC_VERSION GREATER_EQUAL 1900)
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endif()
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endif()
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# Sandboxing: Landlock
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if(NOT SANDBOX_FOUND AND ENABLE_SANDBOX MATCHES "^ON$|^landlock$")
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check_include_file(linux/landlock.h HAVE_LINUX_LANDLOCK_H)
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if(HAVE_LINUX_LANDLOCK_H)
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target_compile_definitions(xz PRIVATE HAVE_LINUX_LANDLOCK_H)
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set(SANDBOX_FOUND ON)
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endif()
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endif()
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if(NOT SANDBOX_FOUND AND NOT ENABLE_SANDBOX MATCHES "^ON$|^OFF$")
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message(SEND_ERROR "ENABLE_SANDBOX=${ENABLE_SANDBOX} was used but "
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"support for the sandboxing method wasn't found.")
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11
configure.ac
11
configure.ac
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@ -519,7 +519,7 @@ AM_CONDITIONAL([COND_DOC], [test x$enable_doc != xno])
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AC_MSG_CHECKING([if sandboxing should be used])
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AC_ARG_ENABLE([sandbox], [AS_HELP_STRING([--enable-sandbox=METHOD],
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[Sandboxing METHOD can be
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'auto', 'no', 'capsicum', or 'pledge'.
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'auto', 'no', 'capsicum', 'pledge', or 'landlock'.
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The default is 'auto' which enables sandboxing if
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a supported sandboxing method is found.])],
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[], [enable_sandbox=auto])
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@ -527,12 +527,12 @@ case $enable_sandbox in
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auto)
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AC_MSG_RESULT([maybe (autodetect)])
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;;
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no | capsicum | pledge)
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no | capsicum | pledge | landlock)
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AC_MSG_RESULT([$enable_sandbox])
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;;
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*)
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AC_MSG_RESULT([])
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AC_MSG_ERROR([--enable-sandbox only accepts 'auto', 'no', 'capsicum', or 'pledge'.])
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AC_MSG_ERROR([--enable-sandbox only accepts 'auto', 'no', 'capsicum', 'pledge', or 'landlock'.])
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;;
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esac
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@ -1059,6 +1059,11 @@ AS_CASE([$enable_sandbox],
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AC_CHECK_FUNCS([pledge], [enable_sandbox=found])
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]
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)
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AS_CASE([$enable_sandbox],
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[auto | landlock], [
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AC_CHECK_HEADERS([linux/landlock.h], [enable_sandbox=found])
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]
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)
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# If a specific sandboxing method was explicitly requested and it wasn't
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# found, give an error.
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@ -33,6 +33,11 @@ static bool warn_fchown;
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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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@ -253,6 +258,59 @@ io_sandbox_enter(int src_fd)
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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 openend. 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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@ -13,6 +13,13 @@
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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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@ -156,6 +163,18 @@ main(int argc, char **argv)
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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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@ -52,7 +52,8 @@
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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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#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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