linux-kernel - [PATCH] fs: Fix double prealloc_shrinker() in sget

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Message-ID: <153131984019.24777.15284245961241666054.stgit@localhost.localdomain>
Date:   Wed, 11 Jul 2018 17:37:34 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, dhowells@...hat.com,
        ktkhai@...tuozzo.com
Subject: [PATCH] fs: Fix double prealloc_shrinker() in sget_fc()

Hi,

I'm observing "KASAN: use-after-free Read in shrink_slab" on recent
linux-next in the code I've added:

https://syzkaller.appspot.com/bug?id=91767fc6346a4b9e0309a8cd7e2f356c434450b9

It seems to be not related to my patchset, since there is
a problem with double preallocation of shrinker. We should
use register_shrinker_prepared() in sget_fc(), since shrinker
is already allocated in alloc_super().

Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
---
 fs/super.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/super.c b/fs/super.c
index 13647d4fd262..47a819f1a300 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -551,7 +551,7 @@ struct super_block *sget_fc(struct fs_context *fc,
 	hlist_add_head(&s->s_instances, &s->s_type->fs_supers);
 	spin_unlock(&sb_lock);
 	get_filesystem(s->s_type);
-	register_shrinker(&s->s_shrink);
+	register_shrinker_prepared(&s->shrinker);
 	return s;
 }
 EXPORT_SYMBOL(sget_fc);