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[PATCH] netfilter: nf_conntrack_sip: CSeq 0 is a valid CSeq

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  [PATCH] netfilter: nf_conntrack_sip: CSeq 0 is a valid CSeq Christophe Leroy <christophe.leroy@c-s.fr> - 2016-07-01 11:50 +0200
    Re: [PATCH] netfilter: nf_conntrack_sip: CSeq 0 is a valid CSeq Liping Zhang <zlpnobody@gmail.com> - 2016-07-04 07:50 +0200
      Re: [PATCH] netfilter: nf_conntrack_sip: CSeq 0 is a valid CSeq Christophe Leroy <christophe.leroy@c-s.fr> - 2016-07-04 08:20 +0200
        Re: [PATCH] netfilter: nf_conntrack_sip: CSeq 0 is a valid CSeq Liping Zhang <zlpnobody@gmail.com> - 2016-07-04 13:50 +0200

#1435218 — [PATCH] netfilter: nf_conntrack_sip: CSeq 0 is a valid CSeq

Do not drop packet when CSeq is 0 as 0 is also a valid value for CSeq.

In order to do so, we replace obsolete simple_strtoul() which
returns 0 on error by kstrtouint(). As kstrtouint() requires a
NULL terminated string, we need to use a temporary buffer

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 net/netfilter/nf_conntrack_sip.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index f72ba55..e770477 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -1368,6 +1368,7 @@ static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
 	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 	unsigned int matchoff, matchlen, matchend;
 	unsigned int code, cseq, i;
+	char buf[21];
 
 	if (*datalen < strlen("SIP/2.0 200"))
 		return NF_ACCEPT;
@@ -1382,8 +1383,13 @@ static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
 		nf_ct_helper_log(skb, ct, "cannot parse cseq");
 		return NF_DROP;
 	}
-	cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
-	if (!cseq) {
+	if (matchlen > sizeof(buf) - 1) {
+		nf_ct_helper_log(skb, ct, "cannot parse cseq (too big)");
+		return NF_DROP;
+	}
+	memcpy(buf, *dptr + matchoff, matchlen);
+	buf[matchlen] = 0;
+	if (kstrtouint(buf, 10, &cseq)) {
 		nf_ct_helper_log(skb, ct, "cannot get cseq");
 		return NF_DROP;
 	}
@@ -1432,6 +1438,7 @@ static int process_sip_request(struct sk_buff *skb, unsigned int protoff,
 
 	for (i = 0; i < ARRAY_SIZE(sip_handlers); i++) {
 		const struct sip_handler *handler;
+		char buf[21];
 
 		handler = &sip_handlers[i];
 		if (handler->request == NULL)
@@ -1445,8 +1452,13 @@ static int process_sip_request(struct sk_buff *skb, unsigned int protoff,
 			nf_ct_helper_log(skb, ct, "cannot parse cseq");
 			return NF_DROP;
 		}
-		cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
-		if (!cseq) {
+		if (matchlen > sizeof(buf) - 1) {
+			nf_ct_helper_log(skb, ct, "cannot parse cseq(too big)");
+			return NF_DROP;
+		}
+		memcpy(buf, *dptr + matchoff, matchlen);
+		buf[matchlen] = 0;
+		if (kstrtouint(buf, 10, &cseq)) {
 			nf_ct_helper_log(skb, ct, "cannot get cseq");
 			return NF_DROP;
 		}
-- 
2.1.0

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#1436284

2016-07-01 17:48 GMT+08:00 Christophe Leroy <christophe.leroy@c-s.fr>:
> Do not drop packet when CSeq is 0 as 0 is also a valid value for CSeq.
>
> --- a/net/netfilter/nf_conntrack_sip.c
> +++ b/net/netfilter/nf_conntrack_sip.c
> @@ -1368,6 +1368,7 @@ static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
>         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
>         unsigned int matchoff, matchlen, matchend;
>         unsigned int code, cseq, i;
> +       char buf[21];
>
>         if (*datalen < strlen("SIP/2.0 200"))
>                 return NF_ACCEPT;
> @@ -1382,8 +1383,13 @@ static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
>                 nf_ct_helper_log(skb, ct, "cannot parse cseq");
>                 return NF_DROP;
>         }
> -       cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
> -       if (!cseq) {

I think there is no need to convert simple_strtoul to kstrtouint, add
a further check seems better?
Like this:
 -       if (!cseq) {
+       if (!cseq && *(*dptr + matchoff) != '0') {

> +       if (matchlen > sizeof(buf) - 1) {
> +               nf_ct_helper_log(skb, ct, "cannot parse cseq (too big)");
> +               return NF_DROP;
> +       }
> +       memcpy(buf, *dptr + matchoff, matchlen);
> +       buf[matchlen] = 0;
> +       if (kstrtouint(buf, 10, &cseq)) {
>                 nf_ct_helper_log(skb, ct, "cannot get cseq");
>                 return NF_DROP;
>         }

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#1436424

Le 04/07/2016 à 07:48, Liping Zhang a écrit :
> 2016-07-01 17:48 GMT+08:00 Christophe Leroy <christophe.leroy@c-s.fr>:
>> Do not drop packet when CSeq is 0 as 0 is also a valid value for CSeq.
>>
>> --- a/net/netfilter/nf_conntrack_sip.c
>> +++ b/net/netfilter/nf_conntrack_sip.c
>> @@ -1368,6 +1368,7 @@ static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
>>         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
>>         unsigned int matchoff, matchlen, matchend;
>>         unsigned int code, cseq, i;
>> +       char buf[21];
>>
>>         if (*datalen < strlen("SIP/2.0 200"))
>>                 return NF_ACCEPT;
>> @@ -1382,8 +1383,13 @@ static int process_sip_response(struct sk_buff *skb, unsigned int protoff,
>>                 nf_ct_helper_log(skb, ct, "cannot parse cseq");
>>                 return NF_DROP;
>>         }
>> -       cseq = simple_strtoul(*dptr + matchoff, NULL, 10);
>> -       if (!cseq) {
>
> I think there is no need to convert simple_strtoul to kstrtouint, add
> a further check seems better?
> Like this:
>  -       if (!cseq) {
> +       if (!cseq && *(*dptr + matchoff) != '0') {
>

And what about an invalid CSeq that would look like CSeq: 0abzk852 ?
Should we check it is 0 + space instead ?

>> +       if (matchlen > sizeof(buf) - 1) {
>> +               nf_ct_helper_log(skb, ct, "cannot parse cseq (too big)");
>> +               return NF_DROP;
>> +       }
>> +       memcpy(buf, *dptr + matchoff, matchlen);
>> +       buf[matchlen] = 0;
>> +       if (kstrtouint(buf, 10, &cseq)) {
>>                 nf_ct_helper_log(skb, ct, "cannot get cseq");
>>                 return NF_DROP;
>>         }

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#1436429

2016-07-04 14:14 GMT+08:00 Christophe Leroy <christophe.leroy@c-s.fr>:
>> I think there is no need to convert simple_strtoul to kstrtouint, add
>> a further check seems better?
>> Like this:
>>  -       if (!cseq) {
>> +       if (!cseq && *(*dptr + matchoff) != '0') {
>>
>
> And what about an invalid CSeq that would look like CSeq: 0abzk852 ?
> Should we check it is 0 + space instead ?

In this case, i.e. some stupid sip clients set CSeq to "0abzk852",
your patch will also fail to detect this "error".

Because for "Cseq", int (*match_len)(...) point to digits_len(see
struct sip_header ct_sip_hdrs definition).
So in this case match_len will just be setted to ONE (not
sizeof("0abzk852")-1), then cseq will be parsed
as 0 by  kstrtouint, not as an error.

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