ipv6: accept 64k - 1 packet length in ip6_find_1stfragopt()

A packet length of exactly IPV6_MAXPLEN is allowed, we should
refuse parsing options only if the size is 64KiB or more.

While at it, remove one extra variable and one assignment which
were also introduced by the commit that introduced the size
check. Checking the sum 'offset + len' and only later adding
'len' to 'offset' doesn't provide any advantage over directly
summing to 'offset' and checking it.

Fixes: 6399f1fae4ec ("ipv6: avoid overflow of offset in ip6_find_1stfragopt")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
index abb2c307fbe8337ce1714e7392072c945ed5af51..a338bbc33cf3cd895fa77e137d6f6389e9a6519c 100644 (file)
--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -86,7 +86,6 @@ int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
 
        while (offset <= packet_len) {
                struct ipv6_opt_hdr *exthdr;
-               unsigned int len;
 
                switch (**nexthdr) {
 
@@ -112,10 +111,9 @@ int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
 
                exthdr = (struct ipv6_opt_hdr *)(skb_network_header(skb) +
                                                 offset);
-               len = ipv6_optlen(exthdr);
-               if (len + offset >= IPV6_MAXPLEN)
+               offset += ipv6_optlen(exthdr);
+               if (offset > IPV6_MAXPLEN)
                        return -EINVAL;
-               offset += len;
                *nexthdr = &exthdr->nexthdr;
        }