RE: [PATCH bpf 1/2] bpf, sockhash: Fix memory leak when unlinking sockets in sock_hash_free

[John Fastabend <john.fastabend@gmail.com>]

Jakub Sitnicki wrote:
> When sockhash gets destroyed while sockets are still linked to it, we will
> walk the bucket lists and delete the links. However, we are not freeing the
> list elements after processing them, leaking the memory.
> 
> The leak can be triggered by close()'ing a sockhash map when it still
> contains sockets, and observed with kmemleak:
> 
>   unreferenced object 0xffff888116e86f00 (size 64):
>     comm "race_sock_unlin", pid 223, jiffies 4294731063 (age 217.404s)
>     hex dump (first 32 bytes):
>       00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>       81 de e8 41 00 00 00 00 c0 69 2f 15 81 88 ff ff  ...A.....i/.....
>     backtrace:
>       [<00000000dd089ebb>] sock_hash_update_common+0x4ca/0x760
>       [<00000000b8219bd5>] sock_hash_update_elem+0x1d2/0x200
>       [<000000005e2c23de>] __do_sys_bpf+0x2046/0x2990
>       [<00000000d0084618>] do_syscall_64+0xad/0x9a0
>       [<000000000d96f263>] entry_SYSCALL_64_after_hwframe+0x49/0xb3
> 
> Fix it by freeing the list element when we're done with it.
> 
> Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
> ---
>  net/core/sock_map.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index 00a26cf2cfe9..ea46f07a22d8 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -1031,6 +1031,7 @@ static void sock_hash_free(struct bpf_map *map)
>  			sock_map_unref(elem->sk, elem);
>  			rcu_read_unlock();
>  			release_sock(elem->sk);
> +			sock_hash_free_elem(htab, elem);
>  		}
>  	}
>  
> -- 
> 2.25.4
> 

In Cilium we pin the map and never release it thanks for catching this.

Acked-by: John Fastabend <john.fastabend@gmail.com>