[PATCH 3.16 129/134] ipv6: avoid overflow of offset in ip6_find_1stfragopt

Ben Hutchings
2017-08-18T13:15:54Z

From: Sabrina Dubroca <sd@queasysnail.net>

commit 6399f1fae4ec29fab5ec76070435555e256ca3a6 upstream.

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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv6/output_core.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -44,7 +44,7 @@ EXPORT_SYMBOL_GPL(ipv6_proxy_select_iden

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;
@@ -52,6 +52,7 @@ int ip6_find_1stfragopt(struct sk_buff *

while (offset <= packet_len) {
struct ipv6_opt_hdr *exthdr;
+ unsigned int len;

switch (**nexthdr) {

@@ -77,7 +78,10 @@ int ip6_find_1stfragopt(struct sk_buff *

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;
}