RE: [PATCH bpf-next 2/4] bpf, sockmap: Fix memleak in tcp_bpf_sendmsg while sk msg is full

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

Wang Yufen wrote:
> If tcp_bpf_sendmsg() is running while sk msg is full, sk_msg_alloc()
> returns -ENOSPC, tcp_bpf_sendmsg() goto wait for memory. If partial memory
> has been alloced by sk_msg_alloc(), that is, msg_tx->sg.size is greater
> than osize after sk_msg_alloc(), memleak occurs. To fix we use
> sk_msg_trim() to release the allocated memory, then goto wait for memory.

Small nit, "sk_msg_alloc() returns -ENOSPC" should be something like, "when
sk_msg_alloc() returns -ENOMEM error,..." That error path is from ENOMEM not
the ENOSPC.

But nice find thanks! I think we might have seen this in a couple cases on
our side as well.

> 
> This issue can cause the following info:
> WARNING: CPU: 3 PID: 7950 at net/core/stream.c:208 sk_stream_kill_queues+0xd4/0x1a0
> Call Trace:
>  <TASK>
>  inet_csk_destroy_sock+0x55/0x110
>  __tcp_close+0x279/0x470
>  tcp_close+0x1f/0x60
>  inet_release+0x3f/0x80
>  __sock_release+0x3d/0xb0
>  sock_close+0x11/0x20
>  __fput+0x92/0x250
>  task_work_run+0x6a/0xa0
>  do_exit+0x33b/0xb60
>  do_group_exit+0x2f/0xa0
>  get_signal+0xb6/0x950
>  arch_do_signal_or_restart+0xac/0x2a0
>  exit_to_user_mode_prepare+0xa9/0x200
>  syscall_exit_to_user_mode+0x12/0x30
>  do_syscall_64+0x46/0x80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>  </TASK>
> 
> WARNING: CPU: 3 PID: 2094 at net/ipv4/af_inet.c:155 inet_sock_destruct+0x13c/0x260
> Call Trace:
>  <TASK>
>  __sk_destruct+0x24/0x1f0
>  sk_psock_destroy+0x19b/0x1c0
>  process_one_work+0x1b3/0x3c0
>  kthread+0xe6/0x110
>  ret_from_fork+0x22/0x30
>  </TASK>
> 
> Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
> Signed-off-by: Wang Yufen <wangyufen@huawei.com>
> ---
>  net/ipv4/tcp_bpf.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> index 9b9b02052fd3..ac9f491cc139 100644
> --- a/net/ipv4/tcp_bpf.c
> +++ b/net/ipv4/tcp_bpf.c
> @@ -421,8 +421,10 @@ static int tcp_bpf_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
>  		osize = msg_tx->sg.size;
>  		err = sk_msg_alloc(sk, msg_tx, msg_tx->sg.size + copy, msg_tx->sg.end - 1);
>  		if (err) {
> -			if (err != -ENOSPC)
> +			if (err != -ENOSPC) {
> +				sk_msg_trim(sk, msg_tx, osize);
>  				goto wait_for_memory;
> +			}
>  			enospc = true;
>  			copy = msg_tx->sg.size - osize;
>  		}
> -- 
> 2.25.1
> 

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