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Date:   Fri,  4 Nov 2016 15:36:49 -0400
From:   Soheil Hassas Yeganeh <>
        Soheil Hassas Yeganeh <>
Subject: [PATCH net] sock: fix sendmmsg for partial sendmsg

From: Soheil Hassas Yeganeh <>

Do not send the next message in sendmmsg for partial sendmsg

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

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

diff --git a/net/socket.c b/net/socket.c
index 5a9bf5e..272518b 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2038,6 +2038,8 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
 		if (err)
+		if (msg_data_left(&msg_sys))
+			break;

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