net: add length argument to skb_copy_and_csum_datagram_iovec

Without this length argument, we can read past the end of the iovec in
memcpy_toiovec because we have no way of knowing the total length of the
iovec's buffers.

This is needed for stable kernels where 89c22d8c ("net: Fix skb
csum races when peeking") has been backported but that don't have the
ioviter conversion, which is almost all the stable trees <= 3.18.

This also fixes a kernel crash for NFS servers when the client uses
 -onfsvers=3,proto=udp to mount the export.
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
[bwh: Backported to 3.2: adjust context in include/linux/skbuff.h]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

include/linux/skbuff.h

@@ -2131,7 +2131,8 @@ extern int	       skb_copy_datagram_iovec(const struct sk_buff *from,
 					       int size);
 extern int	       skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
 							int hlen,
-							struct iovec *iov);
+							struct iovec *iov,
+							int len);
 extern int	       skb_copy_datagram_from_iovec(struct sk_buff *skb,
 						    int offset,
 						    const struct iovec *from,

net/core/datagram.c

@@ -709,6 +709,7 @@ EXPORT_SYMBOL(__skb_checksum_complete);
  *	@skb: skbuff
  *	@hlen: hardware length
  *	@iov: io vector
+ *	@len: amount of data to copy from skb to iov
  *
  *	Caller _must_ check that skb will fit to this iovec.
  *
@@ -718,11 +719,14 @@ EXPORT_SYMBOL(__skb_checksum_complete);
  *			   can be modified!
  */
 int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
-				     int hlen, struct iovec *iov)
+				     int hlen, struct iovec *iov, int len)
 {
 	__wsum csum;
 	int chunk = skb->len - hlen;
 
+	if (chunk > len)
+		chunk = len;
+
 	if (!chunk)
 		return 0;
 

net/ipv4/tcp_input.c

@@ -5198,7 +5198,7 @@ static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
 		err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
 	else
 		err = skb_copy_and_csum_datagram_iovec(skb, hlen,
-						       tp->ucopy.iov);
+						       tp->ucopy.iov, chunk);
 
 	if (!err) {
 		tp->ucopy.len -= chunk;

net/ipv4/udp.c

@@ -1207,7 +1207,7 @@ int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	else {
 		err = skb_copy_and_csum_datagram_iovec(skb,
 						       sizeof(struct udphdr),
-						       msg->msg_iov);
+						       msg->msg_iov, copied);
 
 		if (err == -EINVAL)
 			goto csum_copy_err;

net/ipv6/raw.c

@@ -479,7 +479,7 @@ static int rawv6_recvmsg(struct kiocb *iocb, struct sock *sk,
 			goto csum_copy_err;
 		err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);
 	} else {
-		err = skb_copy_and_csum_datagram_iovec(skb, 0, msg->msg_iov);
+		err = skb_copy_and_csum_datagram_iovec(skb, 0, msg->msg_iov, copied);
 		if (err == -EINVAL)
 			goto csum_copy_err;
 	}

net/ipv6/udp.c

@@ -383,7 +383,8 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
 		err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
 					      msg->msg_iov, copied       );
 	else {
-		err = skb_copy_and_csum_datagram_iovec(skb, sizeof(struct udphdr), msg->msg_iov);
+		err = skb_copy_and_csum_datagram_iovec(skb, sizeof(struct udphdr),
+						       msg->msg_iov, copied);
 		if (err == -EINVAL)
 			goto csum_copy_err;
 	}

net/rxrpc/ar-recvmsg.c

@@ -185,7 +185,8 @@ int rxrpc_recvmsg(struct kiocb *iocb, struct socket *sock,
 						      msg->msg_iov, copy);
 		} else {
 			ret = skb_copy_and_csum_datagram_iovec(skb, offset,
-							       msg->msg_iov);
+							       msg->msg_iov,
+							       copy);
 			if (ret == -EINVAL)
 				goto csum_copy_error;
 		}