ipv6: avoid overflow of offset in ip6_find_1stfragopt
authorSabrina Dubroca <sd@queasysnail.net>
Wed, 19 Jul 2017 20:28:55 +0000 (22:28 +0200)
committerDavid S. Miller <davem@davemloft.net>
Thu, 20 Jul 2017 05:50:14 +0000 (22:50 -0700)
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>
net/ipv6/output_core.c

index e9065b8..abb2c30 100644 (file)
@@ -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;
        }