[Devel] [PATCH rh7] ms/mm/list_lru.c: avoid error-path NULL pointer deref

[Konstantin Khorenko]

Andrey, thank you!

Zhenya, Vasya, please prepare a ReadyKernel patch for it.

https://readykernel.com/

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 06/19/2017 04:41 PM, Andrey Ryabinin wrote:
> From: Alexander Polakov <apolyakov at beget.ru>
>
> commit 1bc11d70b5db7c6bb1414b283d7f09b1fe1ac0d0 upsteram.
>
> As described in https://bugzilla.kernel.org/show_bug.cgi?id=177821:
>
> After some analysis it seems to be that the problem is in alloc_super().
> In case list_lru_init_memcg() fails it goes into destroy_super(), which
> calls list_lru_destroy().
>
> And in list_lru_init() we see that in case memcg_init_list_lru() fails,
> lru->node is freed, but not set NULL, which then leads list_lru_destroy()
> to believe it is initialized and call memcg_destroy_list_lru().
> memcg_destroy_list_lru() in turn can access lru->node[i].memcg_lrus,
> which is NULL.
>
> [akpm at linux-foundation.org: add comment]
> Signed-off-by: Alexander Polakov <apolyakov at beget.ru>
> Acked-by: Vladimir Davydov <vdavydov.dev at gmail.com>
> Cc: Al Viro <viro at zeniv.linux.org.uk>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
>
> https://jira.sw.ru/browse/PSBM-67300
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
> ---
>  mm/list_lru.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 909eca2c820e..84b4c21d78d7 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -532,6 +532,8 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
>  	err = memcg_init_list_lru(lru, memcg_aware);
>  	if (err) {
>  		kfree(lru->node);
> +		/* Do this so a list_lru_destroy() doesn't crash: */
> +		lru->node = NULL;
>  		goto out;
>  	}
>
>