netfilter: nf_ct_tcp: fix incorrect handling of invalid TCP option

Michael M. Builov reported that in the tcp_options and tcp_sack functions
of netfilter TCP conntrack the incorrect handling of invalid TCP option
with too big opsize may lead to read access beyond tcp-packet or buffer
allocated on stack (netfilter bugzilla #738). The fix is to stop parsing
the options at detecting the broken option.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 37bf94394be0..afc4ab7cfe01 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -409,7 +409,7 @@ static void tcp_options(const struct sk_buff *skb,
                         if (opsize < 2) /* "silly options" */
                                 return;
                         if (opsize > length)
-                                break;  /* don't parse partial options */
+                                return; /* don't parse partial options */
 
                         if (opcode == TCPOPT_SACK_PERM
                             && opsize == TCPOLEN_SACK_PERM)
@@ -469,7 +469,7 @@ static void tcp_sack(const struct sk_buff *skb, unsigned int dataoff,
                         if (opsize < 2) /* "silly options" */
                                 return;
                         if (opsize > length)
-                                break;  /* don't parse partial options */
+                                return; /* don't parse partial options */
 
                         if (opcode == TCPOPT_SACK
                             && opsize >= (TCPOLEN_SACK_BASE