[ghak-trim PATCH v1] audit: move put_tree() to avoid trim_trees refcount underflow and UAF

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&gt; Cc: Jan Kara <jack(a)suse.cz&gt; Cc: Will Deacon <will(a)kernel.org&gt; Cc: Alexander Viro <viro(a)zeniv.linux.org.uk&gt; Cc: Seiji Nishikawa <snishika(a)redhat.com&gt; --- kernel/audit_tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c index b2be4e978ba3..2cd7b5694422 100644 --- a/kernel/audit_tree.c +++ b/kernel/audit_tree.c @@ -593,7 +593,6 @@ static void prune_tree_chunks(struct audit_tree *victim, bool tagged) spin_lock(&hash_lock); } spin_unlock(&hash_lock); - put_tree(victim); } /* @@ -602,6 +601,7 @@ static void prune_tree_chunks(struct audit_tree *victim, bool tagged) static void prune_one(struct audit_tree *victim) { prune_tree_chunks(victim, false); + put_tree(victim); } /* trim the uncommitted chunks from tree */ -- 2.27.0