[PATCH 4.9 43/93] ipv6: avoid overflow of offset in ip6_find_1stfragopt

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sabrina Dubroca <s...@queasysnail.net>


[ 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.

Signed-off-by: Sabrina Dubroca <s...@queasysnail.net>
Acked-by: Hannes Frederic Sowa <han...@stressinduktion.org>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/ipv6/output_core.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -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;
        }