[PATCH net] tcp: fix return value for partial writes

[PATCH net] tcp: fix return value for partial writes

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

After my commit, tcp_sendmsg() might restart its loop after
processing socket backlog.

If sk_err is set, we blindly return an error, even though we
copied data to user space before.

We should instead return number of bytes that could be copied,
otherwise user space might resend data and corrupt the stream.

This might happen if another thread is using recvmsg(MSG_ERRQUEUE)
to process timestamps.

Issue was diagnosed by Soheil and Willem, big kudos to them !

Fixes: d41a69f1d390f ("tcp: make tcp_sendmsg() aware of socket backlog")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
---
 net/ipv4/tcp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3251fe71f39f..19e1468bf8ea 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1164,7 +1164,7 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 
 	err = -EPIPE;
 	if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
-		goto out_err;
+		goto do_error;
 
 	sg = !!(sk->sk_route_caps & NETIF_F_SG);
 

Re: [PATCH net] tcp: fix return value for partial writes

[Soheil Hassas Yeganeh]

On Wed, Nov 2, 2016 at 5:41 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> After my commit, tcp_sendmsg() might restart its loop after
> processing socket backlog.
>
> If sk_err is set, we blindly return an error, even though we
> copied data to user space before.
>
> We should instead return number of bytes that could be copied,
> otherwise user space might resend data and corrupt the stream.
>
> This might happen if another thread is using recvmsg(MSG_ERRQUEUE)
> to process timestamps.
>
> Issue was diagnosed by Soheil and Willem, big kudos to them !
>
> Fixes: d41a69f1d390f ("tcp: make tcp_sendmsg() aware of socket backlog")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Willem de Bruijn <willemb@google.com>
> Cc: Soheil Hassas Yeganeh <soheil@google.com>
> Cc: Yuchung Cheng <ycheng@google.com>
> Cc: Neal Cardwell <ncardwell@google.com>

Tested-by: Soheil Hassas Yeganeh <soheil@google.com>

> ---
>  net/ipv4/tcp.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 3251fe71f39f..19e1468bf8ea 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1164,7 +1164,7 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
>
>         err = -EPIPE;
>         if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
> -               goto out_err;
> +               goto do_error;
>
>         sg = !!(sk->sk_route_caps & NETIF_F_SG);
>
>
>

Nice fix. Thanks, Eric!

Re: [PATCH net] tcp: fix return value for partial writes

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 02 Nov 2016 14:41:50 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> After my commit, tcp_sendmsg() might restart its loop after
> processing socket backlog.
> 
> If sk_err is set, we blindly return an error, even though we
> copied data to user space before.
> 
> We should instead return number of bytes that could be copied,
> otherwise user space might resend data and corrupt the stream.
> 
> This might happen if another thread is using recvmsg(MSG_ERRQUEUE)
> to process timestamps.
> 
> Issue was diagnosed by Soheil and Willem, big kudos to them !
> 
> Fixes: d41a69f1d390f ("tcp: make tcp_sendmsg() aware of socket backlog")
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied and queued up for -stable.