This is a note to let you know that I've just added the patch titled audit: move put_tree() to avoid trim_trees refcount underflow and UAF to the 5.13-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: audit-move-put_tree-to-avoid-trim_trees-refcount-underflow-and-uaf.patch and it can be found in the queue-5.13 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 67d69e9d1a6c889d98951c1d74b19332ce0565af Mon Sep 17 00:00:00 2001 From: Richard Guy Briggs <rgb@xxxxxxxxxx> Date: Mon, 23 Aug 2021 22:04:09 -0400 Subject: audit: move put_tree() to avoid trim_trees refcount underflow and UAF From: Richard Guy Briggs <rgb@xxxxxxxxxx> commit 67d69e9d1a6c889d98951c1d74b19332ce0565af upstream. AUDIT_TRIM is expected to be idempotent, but multiple executions resulted in a refcount underflow and use-after-free. git bisect fingered commit fb041bb7c0a9 ("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 8432c7006297 ("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. Cc: Jan Kara <jack@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Seiji Nishikawa <snishika@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Fixes: 8432c7006297 ("audit: Simplify locking around untag_chunk()") Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> [PM: reformatted/cleaned-up the commit description] Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/audit_tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/audit_tree.c +++ b/kernel/audit_tree.c @@ -593,7 +593,6 @@ static void prune_tree_chunks(struct aud spin_lock(&hash_lock); } spin_unlock(&hash_lock); - put_tree(victim); } /* @@ -602,6 +601,7 @@ static void prune_tree_chunks(struct aud static void prune_one(struct audit_tree *victim) { prune_tree_chunks(victim, false); + put_tree(victim); } /* trim the uncommitted chunks from tree */ Patches currently in stable-queue which might be from rgb@xxxxxxxxxx are queue-5.13/audit-move-put_tree-to-avoid-trim_trees-refcount-underflow-and-uaf.patch