Re: [PATCH net] tcp: refine memory limit test in tcp_fragment()

[Christoph Paasch <cpaasch@apple.com>]

> On Jun 21, 2019, at 6:11 AM, Eric Dumazet <edumazet@google.com> wrote:
> 
> tcp_fragment() might be called for skbs in the write queue.
> 
> Memory limits might have been exceeded because tcp_sendmsg() only
> checks limits at full skb (64KB) boundaries.
> 
> Therefore, we need to make sure tcp_fragment() wont punish applications
> that might have setup very low SO_SNDBUF values.
> 
> Fixes: f070ef2ac667 ("tcp: tcp_fragment() should apply sane memory limits")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Reported-by: Christoph Paasch <cpaasch@apple.com>
> ---
> net/ipv4/tcp_output.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)

Tested-by: Christoph Paasch <cpaasch@apple.com>


Thanks!


> 
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 00c01a01b547ec67c971dc25a74c9258563cf871..0ebc33d1c9e5099d163a234930e213ee35e9fbd1 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1296,7 +1296,8 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
>    if (nsize < 0)
>        nsize = 0;
> 
> -    if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf)) {
> +    if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf &&
> +             tcp_queue != TCP_FRAG_IN_WRITE_QUEUE)) {
>        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG);
>        return -ENOMEM;
>    }
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
>