mptcp: fix memory leak in mptcp_subflow_create_socket()

socket malloced  by sock_create_kern() should be release before return
in the error handling, otherwise it cause memory leak.

unreferenced object 0xffff88810910c000 (size 1216):
  comm "00000003_test_m", pid 12238, jiffies 4295050289 (age 54.237s)
  hex dump (first 32 bytes):
    01 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 2f 30 0a 81 88 ff ff  ........./0.....
  backtrace:
    [<00000000e877f89f>] sock_alloc_inode+0x18/0x1c0
    [<0000000093d1dd51>] alloc_inode+0x63/0x1d0
    [<000000005673fec6>] new_inode_pseudo+0x14/0xe0
    [<00000000b5db6be8>] sock_alloc+0x3c/0x260
    [<00000000e7e3cbb2>] __sock_create+0x89/0x620
    [<0000000023e48593>] mptcp_subflow_create_socket+0xc0/0x5e0
    [<00000000419795e4>] __mptcp_socket_create+0x1ad/0x3f0
    [<00000000b2f942e8>] mptcp_stream_connect+0x281/0x4f0
    [<00000000c80cd5cc>] __sys_connect_file+0x14d/0x190
    [<00000000dc761f11>] __sys_connect+0x128/0x160
    [<000000008b14e764>] __x64_sys_connect+0x6f/0xb0
    [<000000007b4f93bd>] do_syscall_64+0xa1/0x530
    [<00000000d3e770b6>] entry_SYSCALL_64_after_hwframe+0x49/0xb3

Fixes: 2303f994b3e1 ("mptcp: Associate MPTCP context with TCP socket")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>

Hello Wei,

On Fri, 12 Jun 2020, Wei Yongjun wrote:

> socket malloced  by sock_create_kern() should be release before return
> in the error handling, otherwise it cause memory leak.
>
> unreferenced object 0xffff88810910c000 (size 1216):
>  comm "00000003_test_m", pid 12238, jiffies 4295050289 (age 54.237s)
>  hex dump (first 32 bytes):
>    01 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00  ................
>    00 00 00 00 00 00 00 00 00 2f 30 0a 81 88 ff ff  ........./0.....
>  backtrace:
>    [<00000000e877f89f>] sock_alloc_inode+0x18/0x1c0
>    [<0000000093d1dd51>] alloc_inode+0x63/0x1d0
>    [<000000005673fec6>] new_inode_pseudo+0x14/0xe0
>    [<00000000b5db6be8>] sock_alloc+0x3c/0x260
>    [<00000000e7e3cbb2>] __sock_create+0x89/0x620
>    [<0000000023e48593>] mptcp_subflow_create_socket+0xc0/0x5e0
>    [<00000000419795e4>] __mptcp_socket_create+0x1ad/0x3f0
>    [<00000000b2f942e8>] mptcp_stream_connect+0x281/0x4f0
>    [<00000000c80cd5cc>] __sys_connect_file+0x14d/0x190
>    [<00000000dc761f11>] __sys_connect+0x128/0x160
>    [<000000008b14e764>] __x64_sys_connect+0x6f/0xb0
>    [<000000007b4f93bd>] do_syscall_64+0xa1/0x530
>    [<00000000d3e770b6>] entry_SYSCALL_64_after_hwframe+0x49/0xb3
>
> Fixes: 2303f994b3e1 ("mptcp: Associate MPTCP context with TCP socket")
> Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
>
> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> index bf132575040d..bbdb74b8bc3c 100644
> --- a/net/mptcp/subflow.c
> +++ b/net/mptcp/subflow.c
> @@ -1053,8 +1053,10 @@ int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
> 	err = tcp_set_ulp(sf->sk, "mptcp");
> 	release_sock(sf->sk);
>
> -	if (err)
> +	if (err) {
> +		sock_release(sf);
> 		return err;
> +	}
>
> 	/* the newly created socket really belongs to the owning MPTCP master
> 	 * socket, even if for additional subflows the allocation is performed
> -- 
> 2.25.1

Thanks for catching this leak. Be sure to specify which git tree this 
should be applied to in the subject line, I'm assuming in this case you'd 
want [PATCH net].

--
Mat Martineau
Intel