sock: fix sendmmsg for partial sendmsg

[ Upstream commit 3023898b ]

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: 228e548e ("net: Add sendmmsg socket system call")
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: we don't have the iov_iter API, so make
 ___sys_sendmsg() calculate and write back the remaining length]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/socket.c

@@ -1898,7 +1898,7 @@ static int copy_msghdr_from_user(struct msghdr *kmsg,
 
 static int ___sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
 			  struct msghdr *msg_sys, unsigned flags,
-			  struct used_address *used_address)
+			  struct used_address *used_address, int *residue)
 {
 	struct compat_msghdr __user *msg_compat =
 	    (struct compat_msghdr __user *)msg;
@@ -2004,6 +2004,8 @@ static int ___sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
 			memcpy(&used_address->name, msg_sys->msg_name,
 			       used_address->name_len);
 	}
+	if (residue && err >= 0)
+		*residue = total_len - err;
 
 out_freectl:
 	if (ctl_buf != ctl)
@@ -2029,7 +2031,7 @@ long __sys_sendmsg(int fd, struct msghdr __user *msg, unsigned flags)
 	if (!sock)
 		goto out;
 
-	err = ___sys_sendmsg(sock, msg, &msg_sys, flags, NULL);
+	err = ___sys_sendmsg(sock, msg, &msg_sys, flags, NULL, NULL);
 
 	fput_light(sock->file, fput_needed);
 out:
@@ -2056,6 +2058,7 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
 	struct compat_mmsghdr __user *compat_entry;
 	struct msghdr msg_sys;
 	struct used_address used_address;
+	int residue;
 
 	if (vlen > UIO_MAXIOV)
 		vlen = UIO_MAXIOV;
@@ -2074,7 +2077,8 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
 	while (datagrams < vlen) {
 		if (MSG_CMSG_COMPAT & flags) {
 			err = ___sys_sendmsg(sock, (struct msghdr __user *)compat_entry,
-					     &msg_sys, flags, &used_address);
+					     &msg_sys, flags, &used_address,
+					     &residue);
 			if (err < 0)
 				break;
 			err = __put_user(err, &compat_entry->msg_len);
@@ -2082,7 +2086,8 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
 		} else {
 			err = ___sys_sendmsg(sock,
 					     (struct msghdr __user *)entry,
-					     &msg_sys, flags, &used_address);
+					     &msg_sys, flags, &used_address,
+					     &residue);
 			if (err < 0)
 				break;
 			err = put_user(err, &entry->msg_len);
@@ -2092,6 +2097,8 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
 		if (err)
 			break;
 		++datagrams;
+		if (residue)
+			break;
 	}
 
 	fput_light(sock->file, fput_needed);