[PATCH] fs: Fix double prealloc_shrinker() in sget_fc()

[PATCH] fs: Fix double prealloc_shrinker() in sget_fc()

[Kirill Tkhai]

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@virtuozzo.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);

Re: [PATCH] fs: Fix double prealloc_shrinker() in sget_fc()

[David Howells]

Kirill Tkhai <ktkhai@virtuozzo.com> wrote:

> 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);
> 

I already folded in a fix from Eric for this, but Al hasn't pulled the updated
tree yet.

David

Re: [PATCH] fs: Fix double prealloc_shrinker() in sget_fc()

[Jia He]

On 7/11/2018 10:37 PM, Kirill Tkhai Wrote:
> 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@virtuozzo.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);

should be &s->shrink here  ?

-- 
Cheers,
Jia