diff mbox series

[2/2] esp6: fix check on ipv6_skip_exthdr's return value

Message ID 20220316121142.3142336-3-steffen.klassert@secunet.com (mailing list archive)
State Accepted
Commit 4db4075f92af2b28f415fc979ab626e6b37d67b6
Delegated to: Netdev Maintainers
Headers show
Series pull request (net): ipsec 2022-03-16 | expand

Checks

Context Check Description
netdev/tree_selection success Guessing tree name failed - patch did not apply

Commit Message

Steffen Klassert March 16, 2022, 12:11 p.m. UTC 
From: Sabrina Dubroca <sd@queasysnail.net>

Commit 5f9c55c8066b ("ipv6: check return value of ipv6_skip_exthdr")
introduced an incorrect check, which leads to all ESP packets over
either TCPv6 or UDPv6 encapsulation being dropped. In this particular
case, offset is negative, since skb->data points to the ESP header in
the following chain of headers, while skb->network_header points to
the IPv6 header:

    IPv6 | ext | ... | ext | UDP | ESP | ...

That doesn't seem to be a problem, especially considering that if we
reach esp6_input_done2, we're guaranteed to have a full set of headers
available (otherwise the packet would have been dropped earlier in the
stack). However, it means that the return value will (intentionally)
be negative. We can make the test more specific, as the expected
return value of ipv6_skip_exthdr will be the (negated) size of either
a UDP header, or a TCP header with possible options.

In the future, we should probably either make ipv6_skip_exthdr
explicitly accept negative offsets (and adjust its return value for
error cases), or make ipv6_skip_exthdr only take non-negative
offsets (and audit all callers).

Fixes: 5f9c55c8066b ("ipv6: check return value of ipv6_skip_exthdr")
Reported-by: Xiumei Mu <xmu@redhat.com>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
 net/ipv6/esp6.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index b0ffbcd5432d..55d604c9b3b3 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -812,8 +812,7 @@  int esp6_input_done2(struct sk_buff *skb, int err)
 		struct tcphdr *th;
 
 		offset = ipv6_skip_exthdr(skb, offset, &nexthdr, &frag_off);
-
-		if (offset < 0) {
+		if (offset == -1) {
 			err = -EINVAL;
 			goto out;
 		}