Patchwork [1/3] netfilter: xt_TCPOPTSTRIP: don't use tcp_hdr()

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Submitter Pablo Neira
Date June 17, 2013, 7:34 p.m.
Message ID <1371497679-14314-2-git-send-email-pablo@netfilter.org>
Download mbox | patch
Permalink /patch/252046/
State Accepted
Headers show

Comments

Pablo Neira - June 17, 2013, 7:34 p.m.
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.

Cc: Florian Westphal <fw@strlen.de>
Reported-by: Phil Oester <kernel@linuxace.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/xt_TCPOPTSTRIP.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
Julian Anastasov - June 17, 2013, 8:30 p.m.
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.

> Cc: Florian Westphal <fw@strlen.de>
> Reported-by: Phil Oester <kernel@linuxace.com>
> 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 <ja@ssi.bg>
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Patch

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)
+		return NF_DROP;
+
 	opt  = (u_int8_t *)tcph;
 
 	/*