Patch "udp: properly support MSG_PEEK with truncated buffers" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

udp: properly support MSG_PEEK with truncated buffers

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
udp-properly-support-msg_peek-with-truncated-buffers.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Wed, 30 Dec 2015 08:51:12 -0500
Subject: udp: properly support MSG_PEEK with truncated buffers

From: Eric Dumazet <[email protected]>

commit 197c949e7798fbf28cfadc69d9ca0c2abbf93191 upstream.

Backport of this upstream commit into stable kernels :
89c22d8c3b27 ("net: Fix skb csum races when peeking") exposed a bug in udp stack vs MSG_PEEK support, when user provides a buffer smaller than skb payload.

In this case, skb_copy_and_csum_datagram_iovec(skb, sizeof(struct udphdr),

                                 msg->msg_iov);

returns -EFAULT.

This bug does not happen in upstream kernels since Al Viro did a great job to replace this into :
skb_copy_and_csum_datagram_msg(skb, sizeof(struct udphdr), msg); This variant is safe vs short buffers.

For the time being, instead reverting Herbert Xu patch and add back skb->ip_summed invalid changes, simply store the result of udp_lib_checksum_complete() so that we avoid computing the checksum a second time, and avoid the problematic skb_copy_and_csum_datagram_iovec() call.

This patch can be applied on recent kernels as it avoids a double checksumming, then backported to stable kernels as a bug fix.

---
 net/ipv4/udp.c |    6 ++++--
 net/ipv6/udp.c |    6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

@@ -1233,6 +1233,7 @@ int udp_recvmsg(struct kiocb *iocb, stru
 	int peeked, off = 0;
 	int err;
 	int is_udplite = IS_UDPLITE(sk);
+	bool checksum_valid = false;
 	bool slow;
 
 	if (flags & MSG_ERRQUEUE)

@@ -1258,11 +1259,12 @@ try_again:
 	 */
 
 	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) {
-		if (udp_lib_checksum_complete(skb))
+		checksum_valid = !udp_lib_checksum_complete(skb);
+		if (!checksum_valid)
 			goto csum_copy_err;
 	}
 
-	if (skb_csum_unnecessary(skb))
+	if (checksum_valid || skb_csum_unnecessary(skb))
 		err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
 					      msg->msg_iov, copied);
 	else {

@@ -389,6 +389,7 @@ int udpv6_recvmsg(struct kiocb *iocb, st
 	int peeked, off = 0;
 	int err;
 	int is_udplite = IS_UDPLITE(sk);
+	bool checksum_valid = false;
 	int is_udp4;
 	bool slow;
 

@@ -420,11 +421,12 @@ try_again:
 	 */
 
 	if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) {
-		if (udp_lib_checksum_complete(skb))
+		checksum_valid = !udp_lib_checksum_complete(skb);
+		if (!checksum_valid)
 			goto csum_copy_err;
 	}
 
-	if (skb_csum_unnecessary(skb))
+	if (checksum_valid || skb_csum_unnecessary(skb))
 		err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
 					      msg->msg_iov, copied);
 	else {

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/tcp_acks_speedup.patch queue-3.14/udp-properly-support-msg_peek-with-truncated-buffers.patch