Re: [PATCH] list_lru: fix memory leak in __memcg_init_list_lru_node

[Michal Hocko]

On Mon 27-05-19 21:32:02, Shakeel Butt wrote:
> Syzbot reported following memory leak:
> 
> ffffffffda RBX: 0000000000000003 RCX: 0000000000441f79
> BUG: memory leak
> unreferenced object 0xffff888114f26040 (size 32):
>   comm "syz-executor626", pid 7056, jiffies 4294948701 (age 39.410s)
>   hex dump (first 32 bytes):
>     40 60 f2 14 81 88 ff ff 40 60 f2 14 81 88 ff ff  @`......@`......
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<0000000018f36b56>] kmemleak_alloc_recursive include/linux/kmemleak.h:55 [inline]
>     [<0000000018f36b56>] slab_post_alloc_hook mm/slab.h:439 [inline]
>     [<0000000018f36b56>] slab_alloc mm/slab.c:3326 [inline]
>     [<0000000018f36b56>] kmem_cache_alloc_trace+0x13d/0x280 mm/slab.c:3553
>     [<0000000055b9a1a5>] kmalloc include/linux/slab.h:547 [inline]
>     [<0000000055b9a1a5>] __memcg_init_list_lru_node+0x58/0xf0 mm/list_lru.c:352
>     [<000000001356631d>] memcg_init_list_lru_node mm/list_lru.c:375 [inline]
>     [<000000001356631d>] memcg_init_list_lru mm/list_lru.c:459 [inline]
>     [<000000001356631d>] __list_lru_init+0x193/0x2a0 mm/list_lru.c:626
>     [<00000000ce062da3>] alloc_super+0x2e0/0x310 fs/super.c:269
>     [<000000009023adcf>] sget_userns+0x94/0x2a0 fs/super.c:609
>     [<0000000052182cd8>] sget+0x8d/0xb0 fs/super.c:660
>     [<0000000006c24238>] mount_nodev+0x31/0xb0 fs/super.c:1387
>     [<0000000006016a76>] fuse_mount+0x2d/0x40 fs/fuse/inode.c:1236
>     [<000000009a61ec1d>] legacy_get_tree+0x27/0x80 fs/fs_context.c:661
>     [<0000000096cd9ef8>] vfs_get_tree+0x2e/0x120 fs/super.c:1476
>     [<000000005b8f472d>] do_new_mount fs/namespace.c:2790 [inline]
>     [<000000005b8f472d>] do_mount+0x932/0xc50 fs/namespace.c:3110
>     [<00000000afb009b4>] ksys_mount+0xab/0x120 fs/namespace.c:3319
>     [<0000000018f8c8ee>] __do_sys_mount fs/namespace.c:3333 [inline]
>     [<0000000018f8c8ee>] __se_sys_mount fs/namespace.c:3330 [inline]
>     [<0000000018f8c8ee>] __x64_sys_mount+0x26/0x30 fs/namespace.c:3330
>     [<00000000f42066da>] do_syscall_64+0x76/0x1a0 arch/x86/entry/common.c:301
>     [<0000000043d74ca0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> This is a simple off by one bug on the error path.

I suspect fault injection has been used here because the object is tiny
to fail the allocation but definitely worth fixing. Thanks!

> Reported-by: syzbot+f90a420dfe2b1b03cb2c@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  mm/list_lru.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 0bdf3152735e..92870be4a322 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -358,7 +358,7 @@ static int __memcg_init_list_lru_node(struct list_lru_memcg *memcg_lrus,
>  	}
>  	return 0;
>  fail:
> -	__memcg_destroy_list_lru_node(memcg_lrus, begin, i - 1);
> +	__memcg_destroy_list_lru_node(memcg_lrus, begin, i);
>  	return -ENOMEM;
>  }
>  
> -- 
> 2.22.0.rc1.257.g3120a18244-goog
> 

-- 
Michal Hocko
SUSE Labs