[PATCH bpf 2/3] bpf, sockmap: fix leak in bpf_tcp_sendmsg wait for mem path

[Daniel Borkmann]

In bpf_tcp_sendmsg() the sk_alloc_sg() may fail. In the case of
ENOMEM, it may also mean that we've partially filled the scatterlist
entries with pages. Later jumping to sk_stream_wait_memory()
we could further fail with an error for several reasons, however
we miss to call free_start_sg() if the local sk_msg_buff was used.

Fixes: 4f738adba30a ("bpf: create tcp_bpf_ulp allowing BPF to monitor socket 
TX/RX data")
Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Acked-by: John Fastabend <john.fastab...@gmail.com>
---
 kernel/bpf/sockmap.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index f7360c4..c4d75c5 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -1048,7 +1048,7 @@ static int bpf_tcp_sendmsg(struct sock *sk, struct msghdr 
*msg, size_t size)
        timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
 
        while (msg_data_left(msg)) {
-               struct sk_msg_buff *m;
+               struct sk_msg_buff *m = NULL;
                bool enospc = false;
                int copy;
 
@@ -1116,8 +1116,11 @@ static int bpf_tcp_sendmsg(struct sock *sk, struct 
msghdr *msg, size_t size)
                set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
 wait_for_memory:
                err = sk_stream_wait_memory(sk, &timeo);
-               if (err)
+               if (err) {
+                       if (m && m != psock->cork)
+                               free_start_sg(sk, m);
                        goto out_err;
+               }
        }
 out_err:
        if (err < 0)
-- 
2.9.5