linux-kernel - [PATCH] mm: shrinkers: fix double kfree on shrinker name

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Date:   Wed, 20 Jul 2022 23:47:55 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] mm: shrinkers: fix double kfree on shrinker name

syzbot is reporting double kfree() at free_prealloced_shrinker() [1], for
destroy_unused_super() calls free_prealloced_shrinker() even if
prealloc_shrinker() returned an error. Explicitly clear shrinker name
when prealloc_shrinker() called kfree().

Link: https://syzkaller.appspot.com/bug?extid=8b481578352d4637f510 [1]
Reported-by: syzbot <syzbot+8b481578352d4637f510@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Fixes: e33c267ab70de424 ("mm: shrinkers: provide shrinkers with names")
---
 mm/vmscan.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 64ffdcd019a9..3302d9ed332e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -707,8 +707,10 @@ int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
 		return -ENOMEM;
 
 	err = __register_shrinker(shrinker);
-	if (err)
+	if (err) {
 		kfree_const(shrinker->name);
+		shrinker->name = NULL;
+	}
 	return err;
 }
 #else
-- 
2.18.4