ipv6: avoid overflow of offset in ip6_find_1stfragopt

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 <sd@queasysnail.net>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 2 deletions

diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
index e9065b8d3af8..abb2c307fbe8 100644
--- 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 *skb, u8 **nexthdr)
 
         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 *skb, u8 **nexthdr)
 
                 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;
         }