kernel: udp: properly support MSG_PEEK with truncated buffers (#1097)

Add upstream patch to fix CVE-2016-10229

patches/openwrt/0098-udp-properly-support-MSG_PEEK-with-truncated-buffers.patch

@@ -0,0 +1,109 @@
From: Jan Niehusmann <jan@gondor.com>
Date: Fri, 14 Apr 2017 21:26:27 +0200
Subject: udp: properly support MSG_PEEK with truncated buffers

Add upstream patch to fix CVE-2016-10229

diff --git a/target/linux/generic/patches-3.18/001-udp-properly-support-MSG_PEEK-with-truncated-buffers.patch b/target/linux/generic/patches-3.18/001-udp-properly-support-MSG_PEEK-with-truncated-buffers.patch
new file mode 100644
index 0000000000000000000000000000000000000000..16edc8c8da4ce8edf3ce1b5c2a56d543f9658897
--- /dev/null
+++ b/target/linux/generic/patches-3.18/001-udp-properly-support-MSG_PEEK-with-truncated-buffers.patch
@@ -0,0 +1,97 @@
+From 69335972b1c1c9bd7597fc6080b6eb1bd3fbf774 Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Wed, 30 Dec 2015 08:51:12 -0500
+Subject: [PATCH] udp: properly support MSG_PEEK with truncated buffers
+
+[ Upstream commit 197c949e7798fbf28cfadc69d9ca0c2abbf93191 ]
+
+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.
+
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
+---
+ net/ipv4/udp.c | 6 ++++--
+ net/ipv6/udp.c | 6 ++++--
+ 2 files changed, 8 insertions(+), 4 deletions(-)
+
+diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
+index 2a5d388..ee26711 100644
+--- a/net/ipv4/udp.c
++++ b/net/ipv4/udp.c
+@@ -1252,6 +1252,7 @@ int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
+ 	int peeked, off = 0;
+ 	int err;
+ 	int is_udplite = IS_UDPLITE(sk);
++	bool checksum_valid = false;
+ 	bool slow;
+ 
+ 	if (flags & MSG_ERRQUEUE)
+@@ -1277,11 +1278,12 @@ 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 {
+diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
+index 7d01116..143e6c7 100644
+--- a/net/ipv6/udp.c
++++ b/net/ipv6/udp.c
+@@ -388,6 +388,7 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
+ 	int peeked, off = 0;
+ 	int err;
+ 	int is_udplite = IS_UDPLITE(sk);
++	bool checksum_valid = false;
+ 	int is_udp4;
+ 	bool slow;
+ 
+@@ -419,11 +420,12 @@ 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 {
+-- 
+2.1.4
+