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Merge pull request #34480 from yuwata/test-seccomp-suppress-sync

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seccomp-util: pass negative fds as is to fsync() and friends
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Yu Watanabe 2024-09-20 08:27:33 +09:00 committed by GitHub
commit 754d6414f8
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2 changed files with 72 additions and 7 deletions
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27
src/shared/seccomp-util.c
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@ -879,6 +879,7 @@ const SyscallFilterSet syscall_filter_sets[_SYSCALL_FILTER_SET_MAX] = {
.name = "@sync",
.help = "Synchronize files and memory to storage",
.value =
/* Please also update the list in seccomp_suppress_sync(). */
"fdatasync\0"
"fsync\0"
"msync\0"
@ -2464,8 +2465,10 @@ int seccomp_suppress_sync(void) {
uint32_t arch;
int r;
/* This is mostly identical to SystemCallFilter=~@sync:0, but simpler to use, and separately
* manageable, and also masks O_SYNC/O_DSYNC */
/* This behaves slightly differently from SystemCallFilter=~@sync:0, in that negative fds (which
* we can determine to be invalid) are still refused with EBADF. See #34478.
*
* Additionally, O_SYNC/O_DSYNC are masked. */
SECCOMP_FOREACH_LOCAL_ARCH(arch) {
_cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
@ -2483,11 +2486,21 @@ int seccomp_suppress_sync(void) {
continue;
}
r = seccomp_rule_add_exact(
seccomp,
SCMP_ACT_ERRNO(0), /* success → we want this to be a NOP after all */
id,
0);
if (STR_IN_SET(c, "fdatasync", "fsync", "sync_file_range", "sync_file_range2", "syncfs"))
r = seccomp_rule_add_exact(
seccomp,
SCMP_ACT_ERRNO(0), /* success → we want this to be a NOP after all */
id,
1,
SCMP_A0(SCMP_CMP_LE, INT_MAX)); /* The rule handles arguments in unsigned. Hence, this
* means non-negative fd matches the rule, and the negative
* fd passed to the syscall (then it fails with EBADF). */
else
r = seccomp_rule_add_exact(
seccomp,
SCMP_ACT_ERRNO(0), /* success → we want this to be a NOP after all */
id,
0);
if (r < 0)
log_debug_errno(r, "Failed to add filter for system call %s, ignoring: %m", c);
}

52
src/test/test-seccomp.c
View File

@ -18,6 +18,7 @@
#include "capability-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "fs-util.h"
#include "macro.h"
#include "memory-util.h"
#include "missing_sched.h"
@ -1229,4 +1230,55 @@ TEST(restrict_suid_sgid) {
assert_se(wait_for_terminate_and_check("suidsgidseccomp", pid, WAIT_LOG) == EXIT_SUCCESS);
}
static void test_seccomp_suppress_sync_child(void) {
_cleanup_(unlink_and_freep) char *path = NULL;
_cleanup_close_ int fd = -EBADF;
ASSERT_OK(tempfn_random("/tmp/seccomp_suppress_sync", NULL, &path));
ASSERT_OK_ERRNO(fd = open(path, O_RDWR | O_CREAT | O_SYNC | O_CLOEXEC, 0666));
fd = safe_close(fd);
ASSERT_ERROR_ERRNO(fdatasync(-1), EBADF);
ASSERT_ERROR_ERRNO(fsync(-1), EBADF);
ASSERT_ERROR_ERRNO(syncfs(-1), EBADF);
ASSERT_ERROR_ERRNO(fdatasync(INT_MAX), EBADF);
ASSERT_ERROR_ERRNO(fsync(INT_MAX), EBADF);
ASSERT_ERROR_ERRNO(syncfs(INT_MAX), EBADF);
ASSERT_OK(seccomp_suppress_sync());
ASSERT_ERROR_ERRNO(fd = open(path, O_RDWR | O_CREAT | O_SYNC | O_CLOEXEC, 0666), EINVAL);
ASSERT_OK_ERRNO(fdatasync(INT_MAX));
ASSERT_OK_ERRNO(fsync(INT_MAX));
ASSERT_OK_ERRNO(syncfs(INT_MAX));
ASSERT_ERROR_ERRNO(fdatasync(-1), EBADF);
ASSERT_ERROR_ERRNO(fsync(-1), EBADF);
ASSERT_ERROR_ERRNO(syncfs(-1), EBADF);
}
TEST(seccomp_suppress_sync) {
pid_t pid;
if (!is_seccomp_available()) {
log_notice("Seccomp not available, skipping %s", __func__);
return;
}
if (!have_seccomp_privs()) {
log_notice("Not privileged, skipping %s", __func__);
return;
}
ASSERT_OK_ERRNO(pid = fork());
if (pid == 0) {
test_seccomp_suppress_sync_child();
_exit(EXIT_SUCCESS);
}
ASSERT_EQ(wait_for_terminate_and_check("seccomp_suppress_sync", pid, WAIT_LOG), EXIT_SUCCESS);
}
DEFINE_TEST_MAIN(LOG_DEBUG);