ipv6: avoid overflow of offset in ip6_find_1stfragopt

Orabug: 26540159
CVE: CVE-2017-7542

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>
(cherry picked from commit 6399f1fae4ec29fab5ec76070435555e256ca3a6)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>

diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
index 1b933dfc44ca5aa6e7c1d60b1301b4e8b4c861c2..07acd3368b10808739242283624e1d9fe74bc928 100644 (file)
--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -77,7 +77,7 @@ 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;
@@ -85,6 +85,7 @@ int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
 
        while (offset <= packet_len) {
                struct ipv6_opt_hdr *exthdr;
+               unsigned int len;
 
                switch (**nexthdr) {
 
@@ -110,7 +111,10 @@ 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;
        }