linux-kernel - [PATCH AUTOSEL 5.15 05/10] percpu_ref_init(): clean ->percpu_count

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Message-Id: <20220524160009.826957-5-sashal@kernel.org>
Date:   Tue, 24 May 2022 12:00:02 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        syzbot+5b1e53987f858500ec00@...kaller.appspotmail.com,
        Sasha Levin <sashal@...nel.org>, dennis@...nel.org,
        tj@...nel.org, cl@...ux.com, linux-mm@...ck.org
Subject: [PATCH AUTOSEL 5.15 05/10] percpu_ref_init(): clean ->percpu_count_ref on failure

From: Al Viro <viro@...iv.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@...kaller.appspotmail.com
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.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