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seccomp use-after-free fix

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- Add logic for making some seccomp flags exclusive (Tycho)
 - Update selftests for exclusivity testing (Kees)
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Merge tag 'seccomp-v5.1-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull seccomp fixes from Kees Cook:
 "Syzbot found a use-after-free bug in seccomp due to flags that should
  not be allowed to be used together.

  Tycho fixed this, I updated the self-tests, and the syzkaller PoC has
  been running for several days without triggering KASan (before this
  fix, it would reproduce). These patches have also been in -next for
  almost a week, just to be sure.

   - Add logic for making some seccomp flags exclusive (Tycho)

   - Update selftests for exclusivity testing (Kees)"

* tag 'seccomp-v5.1-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  seccomp: Make NEW_LISTENER and TSYNC flags exclusive
  selftests/seccomp: Prepare for exclusive seccomp flags
This commit is contained in:
Linus Torvalds 2019-04-29 13:24:34 -07:00
commit 83a50840e7
2 changed files with 40 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
kernel/seccomp.c
View File

@ -502,7 +502,10 @@ out:
*
* Caller must be holding current->sighand->siglock lock.
*
* Returns 0 on success, -ve on error.
* Returns 0 on success, -ve on error, or
* - in TSYNC mode: the pid of a thread which was either not in the correct
* seccomp mode or did not have an ancestral seccomp filter
* - in NEW_LISTENER mode: the fd of the new listener
*/
static long seccomp_attach_filter(unsigned int flags,
struct seccomp_filter *filter)
@ -1258,6 +1261,16 @@ static long seccomp_set_mode_filter(unsigned int flags,
if (flags & ~SECCOMP_FILTER_FLAG_MASK)
return -EINVAL;
/*
* In the successful case, NEW_LISTENER returns the new listener fd.
* But in the failure case, TSYNC returns the thread that died. If you
* combine these two flags, there's no way to tell whether something
* succeeded or failed. So, let's disallow this combination.
*/
if ((flags & SECCOMP_FILTER_FLAG_TSYNC) &&
(flags & SECCOMP_FILTER_FLAG_NEW_LISTENER))
return -EINVAL;
/* Prepare the new filter before holding any locks. */
prepared = seccomp_prepare_user_filter(filter);
if (IS_ERR(prepared))
@ -1304,7 +1317,7 @@ out:
mutex_unlock(&current->signal->cred_guard_mutex);
out_put_fd:
if (flags & SECCOMP_FILTER_FLAG_NEW_LISTENER) {
if (ret < 0) {
if (ret) {
listener_f->private_data = NULL;
fput(listener_f);
put_unused_fd(listener);

34
tools/testing/selftests/seccomp/seccomp_bpf.c
View File

@ -2166,11 +2166,14 @@ TEST(detect_seccomp_filter_flags)
SECCOMP_FILTER_FLAG_LOG,
SECCOMP_FILTER_FLAG_SPEC_ALLOW,
SECCOMP_FILTER_FLAG_NEW_LISTENER };
unsigned int flag, all_flags;
unsigned int exclusive[] = {
SECCOMP_FILTER_FLAG_TSYNC,
SECCOMP_FILTER_FLAG_NEW_LISTENER };
unsigned int flag, all_flags, exclusive_mask;
int i;
long ret;
/* Test detection of known-good filter flags */
/* Test detection of individual known-good filter flags */
for (i = 0, all_flags = 0; i < ARRAY_SIZE(flags); i++) {
int bits = 0;
@ -2197,16 +2200,29 @@ TEST(detect_seccomp_filter_flags)
all_flags |= flag;
}
/* Test detection of all known-good filter flags */
ret = seccomp(SECCOMP_SET_MODE_FILTER, all_flags, NULL);
EXPECT_EQ(-1, ret);
EXPECT_EQ(EFAULT, errno) {
TH_LOG("Failed to detect that all known-good filter flags (0x%X) are supported!",
all_flags);
/*
* Test detection of all known-good filter flags combined. But
* for the exclusive flags we need to mask them out and try them
* individually for the "all flags" testing.
*/
exclusive_mask = 0;
for (i = 0; i < ARRAY_SIZE(exclusive); i++)
exclusive_mask |= exclusive[i];
for (i = 0; i < ARRAY_SIZE(exclusive); i++) {
flag = all_flags & ~exclusive_mask;
flag |= exclusive[i];
ret = seccomp(SECCOMP_SET_MODE_FILTER, flag, NULL);
EXPECT_EQ(-1, ret);
EXPECT_EQ(EFAULT, errno) {
TH_LOG("Failed to detect that all known-good filter flags (0x%X) are supported!",
flag);
}
}
/* Test detection of an unknown filter flag */
/* Test detection of an unknown filter flags, without exclusives. */
flag = -1;
flag &= ~exclusive_mask;
ret = seccomp(SECCOMP_SET_MODE_FILTER, flag, NULL);
EXPECT_EQ(-1, ret);
EXPECT_EQ(EINVAL, errno) {