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

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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>
This commit is contained in:
Stefano Brivio 2017-08-18 14:40:53 +02:00 committed by David S. Miller
parent 6470812e22
commit 3de33e1ba0
1 changed files with 2 additions and 4 deletions
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6
net/ipv6/output_core.c
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@ -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;
}