Re: [ghak-trim PATCH v1] audit: move put_tree() to avoid trim_trees refcount underflow and UAF
On Mon, Aug 23, 2021 at 10:05 PM Richard Guy Briggs <rgb(a)redhat.com> wrote:
AUDIT_TRIM is expected to be idempotent, but multiple executions resulted in a
refcount underflow and use-after-free.
git bisect fingered commit fb041bb7c0a918b95c6889fc965cdc4a75b4c0ca (2019-11)
("locking/refcount: Consolidate implementations of refcount_t")
but this patch with its more thorough checking that wasn't in the x86 assembly
code merely exposed a previously existing tree refcount imbalance in the case
of tree trimming code that was refactored with prune_one() to remove a tree
introduced in commit 8432c70062978d9a57bde6715496d585ec520c3e (2018-11)
("audit: Simplify locking around untag_chunk()")
Move the put_tree() to cover only the prune_one() case.
Passes audit-testsuite and 3 passes of "auditctl -t" with at least one
directory watch.
Fixes: 8432c7006297 ("audit: Simplify locking around untag_chunk()")
Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
Cc: Jan Kara <jack(a)suse.cz>
Cc: Will Deacon <will(a)kernel.org>
Cc: Alexander Viro <viro(a)zeniv.linux.org.uk>
Cc: Seiji Nishikawa <snishika(a)redhat.com>
---
kernel/audit_tree.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
First a quick comment about the commit description, when referencing
specific commits in the description please use the same format that
you used in the "Fixes:" tag; it makes the description easier to read.
No need to resend, I fixed it when I merged your patch, but something
to keep in mind for the future.
As for the patch itself, thanks for finding this and sending a fix.
Normally this is something I would send up to Linus at the end of the
week during the -rcX phase, but since we are currently at -rc7 I'm
going to simply add the -stable marking and merge it into audit/next
to get pushed up to Linus early next week, assuming we see v5.14
released this Sunday. If for some reason we see a v5.14-rc8 next week
I'll adjust things and send it to Linus as a -stable patch.
--
paul moore
www.paul-moore.com