Subject: [PATCH 13/16] sock: fix sendmmsg for partial sendmsg

From: Soheil Hassas Yeganeh <[email-masked]>
Date: Fri, 4 Nov 2016 15:36:49 -0400

[ Upstream commit 3023898b7d4aac65987bd2f485cc22390aae6f78 ]

Do not send the next message in sendmmsg for partial sendmsg
invocations.

sendmmsg assumes that it can continue sending the next message
when the return value of the individual sendmsg invocations
is positive. It results in corrupting the data for TCP,
SCTP, and UNIX streams.

For example, sendmmsg([["abcd"], ["efgh"]]) can result in a stream
of "aefgh" if the first sendmsg invocation sends only the first
byte while the second sendmsg goes through.

Datagram sockets either send the entire datagram or fail, so
this patch affects only sockets of type SOCK_STREAM and
SOCK_SEQPACKET.

Fixes: 228e548e6020 ("net: Add sendmmsg socket system call")
Signed-off-by: Soheil Hassas Yeganeh <[email-masked]>
Signed-off-by: Eric Dumazet <[email-masked]>
Signed-off-by: Willem de Bruijn <[email-masked]>
Signed-off-by: Neal Cardwell <[email-masked]>
Acked-by: Maciej Żenczykowski <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/socket.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/socket.c b/net/socket.c
index 263b334..0090225 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2041,6 +2041,8 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
 		if (err)
 			break;
 		++datagrams;
+		if (msg_data_left(&msg_sys))
+			break;
 	}
 
 	fput_light(sock->file, fput_needed);
-- 
2.7.4