Re: [PATCH 1/3] netfilter: xt_TCPOPTSTRIP: don't use tcp_hdr()
From: Julian Anastasov <ja@ssi.bg>
Date: 2013-06-17 20:30:45
Also in:
netfilter-devel
Hello, On Mon, 17 Jun 2013, Pablo Neira Ayuso wrote:
In (bc6bcb5 netfilter: xt_TCPOPTSTRIP: fix possible mangling beyond packet boundary), the use of tcp_hdr was introduced. However, we cannot assume that skb->transport_header is set for non-local packets.
It is hidden also in tcp_hdrlen() which is used here.
quoted hunk ↗ jump to hunk
Cc: Florian Westphal <fw@strlen.de> Reported-by: Phil Oester <redacted> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> --- net/netfilter/xt_TCPOPTSTRIP.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)diff --git a/net/netfilter/xt_TCPOPTSTRIP.c b/net/netfilter/xt_TCPOPTSTRIP.c index 1eb1a44..b68fa19 100644 --- a/net/netfilter/xt_TCPOPTSTRIP.c +++ b/net/netfilter/xt_TCPOPTSTRIP.c@@ -48,11 +48,13 @@ tcpoptstrip_mangle_packet(struct sk_buff *skb, return NF_DROP; len = skb->len - tcphoff; - if (len < (int)sizeof(struct tcphdr) || - tcp_hdr(skb)->doff * 4 > len) + if (len < (int)sizeof(struct tcphdr)) return NF_DROP; tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff); + if (tcph->doff * 4 > len)
We can save tcph->doff * 4 in a var and use it instead of tcp_hdrlen. BTW, optlen() touches opt[offset+1] unsafely when i == tcp_hdrlen(skb) - 1.
+ return NF_DROP; + opt = (u_int8_t *)tcph; /* -- 1.7.10.4
Regards -- Julian Anastasov [off-list ref]