Patch "ipv6: avoid overflow of offset in ip6_find_1stfragopt" has been added to the 4.4-stable tree

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

ipv6: avoid overflow of offset in ip6_find_1stfragopt

to the 4.4-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:
ipv6-avoid-overflow-of-offset-in-ip6_find_1stfragopt.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Sabrina Dubroca <[email protected]>
Date: Wed, 19 Jul 2017 22:28:55 +0200
Subject: ipv6: avoid overflow of offset in ip6_find_1stfragopt

From: Sabrina Dubroca <[email protected]>

[ Upstream commit 6399f1fae4ec29fab5ec76070435555e256ca3a6 ]

In some cases, offset can overflow and can cause an infinite loop in ip6_find_1stfragopt(). Make it unsigned int to prevent the overflow, and cap it at IPV6_MAXPLEN, since packets larger than that should be invalid.

This problem has been here since before the beginning of git history.

---
 net/ipv6/output_core.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

@@ -78,7 +78,7 @@ EXPORT_SYMBOL(ipv6_select_ident);
 
 int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
 {
-	u16 offset = sizeof(struct ipv6hdr);
+	unsigned int offset = sizeof(struct ipv6hdr);
 	unsigned int packet_len = skb_tail_pointer(skb) -
 		skb_network_header(skb);
 	int found_rhdr = 0;

@@ -86,6 +86,7 @@ int ip6_find_1stfragopt(struct sk_buff *
 
 	while (offset <= packet_len) {
 		struct ipv6_opt_hdr *exthdr;
+		unsigned int len;
 
 		switch (**nexthdr) {
 

@@ -111,7 +112,10 @@ int ip6_find_1stfragopt(struct sk_buff *
 
 		exthdr = (struct ipv6_opt_hdr *)(skb_network_header(skb) +
 						 offset);
-		offset += ipv6_optlen(exthdr);
+		len = ipv6_optlen(exthdr);
+		if (len + offset >= IPV6_MAXPLEN)
+			return -EINVAL;
+		offset += len;
 		*nexthdr = &exthdr->nexthdr;
 	}
 

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

queue-4.4/ipv6-avoid-overflow-of-offset-in-ip6_find_1stfragopt.patch