Commit 0634c0f9 authored Aug 23, 2021 by Richard Guy Briggs Committed by Greg Kroah-Hartman Sep 03, 2021

audit: move put_tree() to avoid trim_trees refcount underflow and UAF



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 8432c700 ("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@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Seiji Nishikawa <snishika@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 8432c700 ("audit: Simplify locking around untag_chunk()")
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
[PM: reformatted/cleaned-up the commit description]
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent cab00033

kernel/audit_tree.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -595,7 +595,6 @@ static void prune_tree_chunks(struct audit_tree *victim, bool tagged)
		spin_lock(&hash_lock);
		}
		spin_unlock(&hash_lock);
		put_tree(victim);
		}

		/*
		@@ -604,6 +603,7 @@ 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 */