[PATCH 027/104] net: ipv6: tcp: fix potential use after free in tcp_v6_do_rcv

[Kamal Mostafa]

3.8.13.11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Borkmann <dborkman@xxxxxxxxxx>

[ Upstream commit 3a1c756590633c0e86df606e5c618c190926a0df ]

In tcp_v6_do_rcv() code, when processing pkt options, we soley work
on our skb clone opt_skb that we've created earlier before entering
tcp_rcv_established() on our way. However, only in condition ...

  if (np->rxopt.bits.rxtclass)
    np->rcv_tclass = ipv6_get_dsfield(ipv6_hdr(skb));

... we work on skb itself. As we extract every other information out
of opt_skb in ipv6_pktoptions path, this seems wrong, since skb can
already be released by tcp_rcv_established() earlier on. When we try
to access it in ipv6_hdr(), we will dereference freed skb.

[ Bug added by commit 4c507d2897bd9b ("net: implement IP_RECVTOS for
  IP_PKTOPTIONS") ]

Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Acked-by: Jiri Benc <jbenc@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[ kamal: backport to 3.8 ]
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
 net/ipv6/tcp_ipv6.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 4cc834a..2eb71b4 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1468,7 +1468,7 @@ ipv6_pktoptions:
 		if (np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim)
 			np->mcast_hops = ipv6_hdr(opt_skb)->hop_limit;
 		if (np->rxopt.bits.rxtclass)
-			np->rcv_tclass = ipv6_tclass(ipv6_hdr(skb));
+			np->rcv_tclass = ipv6_tclass(ipv6_hdr(opt_skb));
 		if (ipv6_opt_accepted(sk, opt_skb)) {
 			skb_set_owner_r(opt_skb, sk);
 			opt_skb = xchg(&np->pktoptions, opt_skb);
-- 
1.8.1.2

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