Re: [PATCH] mm/slub: fix to return errno if kmalloc() fails

From: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
To: Chao Yu <chao@kernel.org>, linux-mm@kvack.org
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	jaegeuk@kernel.org, Chao Yu <chao.yu@oppo.com>,
	vbabka@kernel.org, muchun.song@linux.dev
Subject: Re: [PATCH] mm/slub: fix to return errno if kmalloc() fails
Date: Fri, 9 Sep 2022 18:47:49 +0200	[thread overview]
Message-ID: <2025305d-16db-abdf-6cd3-1fb93371c2b4@wanadoo.fr> (raw)
In-Reply-To: <20220830141009.150075-1-chao@kernel.org>

Le 30/08/2022 à 16:10, Chao Yu a écrit :
> From: Chao Yu <chao.yu@oppo.com>
> 
> In create_unique_id(), kmalloc(, GFP_KERNEL) can fail due to
> out-of-memory, if it fails, return errno correctly rather than
> triggering panic via BUG_ON();
> 
> kernel BUG at mm/slub.c:5893!
> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
> 
> Call trace:
>   sysfs_slab_add+0x258/0x260 mm/slub.c:5973
>   __kmem_cache_create+0x60/0x118 mm/slub.c:4899
>   create_cache mm/slab_common.c:229 [inline]
>   kmem_cache_create_usercopy+0x19c/0x31c mm/slab_common.c:335
>   kmem_cache_create+0x1c/0x28 mm/slab_common.c:390
>   f2fs_kmem_cache_create fs/f2fs/f2fs.h:2766 [inline]
>   f2fs_init_xattr_caches+0x78/0xb4 fs/f2fs/xattr.c:808
>   f2fs_fill_super+0x1050/0x1e0c fs/f2fs/super.c:4149
>   mount_bdev+0x1b8/0x210 fs/super.c:1400
>   f2fs_mount+0x44/0x58 fs/f2fs/super.c:4512
>   legacy_get_tree+0x30/0x74 fs/fs_context.c:610
>   vfs_get_tree+0x40/0x140 fs/super.c:1530
>   do_new_mount+0x1dc/0x4e4 fs/namespace.c:3040
>   path_mount+0x358/0x914 fs/namespace.c:3370
>   do_mount fs/namespace.c:3383 [inline]
>   __do_sys_mount fs/namespace.c:3591 [inline]
>   __se_sys_mount fs/namespace.c:3568 [inline]
>   __arm64_sys_mount+0x2f8/0x408 fs/namespace.c:3568
> 
> Cc: <stable@kernel.org>
> Reported-by: syzbot+81684812ea68216e08c5@syzkaller.appspotmail.com
> Signed-off-by: Chao Yu <chao.yu@oppo.com>
> ---
>   mm/slub.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 862dbd9af4f5..e6f3727b9ad2 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5890,7 +5890,8 @@ static char *create_unique_id(struct kmem_cache *s)
>   	char *name = kmalloc(ID_STR_LENGTH, GFP_KERNEL);

Hi,

looks that ID_STR_LENGTH could even be reduced to 32 or 16.

The 2nd BUG_ON at the end of the function could certainly be just 
removed as well or remplaced by a:
    	if (p > name + ID_STR_LENGTH - 1) {
		kfree(name);
		return -E<something>;
	}

Just my 2c,

CJ

>   	char *p = name;
>   
> -	BUG_ON(!name);
> +	if (!name)
> +		return ERR_PTR(-ENOMEM);
>   
>   	*p++ = ':';
>   	/*
> @@ -5948,6 +5949,8 @@ static int sysfs_slab_add(struct kmem_cache *s)
>   		 * for the symlinks.
>   		 */
>   		name = create_unique_id(s);
> +		if (IS_ERR(name))
> +			return PTR_ERR(name);
>   	}
>   
>   	s->kobj.kset = kset;