[PATCH 5.17 06/75] percpu_ref_init(): clean ->percpu_count_ref on failure

Greg Kroah-Hartman
2022-06-03T18:09:29Z

From: Al Viro <viro@zeniv.linux.org.uk>

[ Upstream commit a91714312eb16f9ecd1f7f8b3efe1380075f28d4 ]

That way percpu_ref_exit() is safe after failing percpu_ref_init().
At least one user (cgroup_create()) had a double-free that way;
there might be other similar bugs. Easier to fix in percpu_ref_init(),
rather than playing whack-a-mole in sloppy users...

Usual symptoms look like a messed refcounting in one of subsystems
that use percpu allocations (might be percpu-refcount, might be
something else). Having refcounts for two different objects share
memory is Not Nice(tm)...

Reported-by: syzbot+5b1e53987f858500ec00@syzkaller.appspotmail.com
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
lib/percpu-refcount.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index af9302141bcf..e5c5315da274 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -76,6 +76,7 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
data = kzalloc(sizeof(*ref->data), gfp);
if (!data) {
free_percpu((void __percpu *)ref->percpu_count_ptr);
+ ref->percpu_count_ptr = 0;
return -ENOMEM;
}

--
2.35.1