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seccomp-util: pass negative fds as is to fsync() and friends

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Closes #34478.

Co-authored-by: Mike Yuan <me@yhndnzj.com>
This commit is contained in:
Yu Watanabe
2024-09-20 03:52:19 +09:00
parent a3c2a9ee5d
commit 144fbbac23
1 changed files with 20 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);
}