[PATCH net v2] sctp: asconf's process should verify address parameter is in the beginning

[PATCH net v2] sctp: asconf's process should verify address parameter is in the beginning

[Xin Long]

in sctp_process_asconf(), we get address parameter from the beginning of
the addip params. but we never check if it's really there. if the addr
param is not there, it still can pass sctp_verify_asconf(), then to be
handled by sctp_process_asconf(), it will not be safe.

so add a code in sctp_verify_asconf() to check the address parameter is in
the beginning, or return false to send abort.

v1->v2:
 * put the check behind the params' length verify.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/sm_make_chunk.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 06320c8..89a4d1c 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -3166,6 +3166,13 @@ bool sctp_verify_asconf(const struct sctp_association *asoc,
 		return false;
 	if (!addr_param_needed && addr_param_seen)
 		return false;
+	if (addr_param_needed && addr_param_seen) {
+		/* Ensure the address parameter is in the beginning */
+		param.v = chunk->skb->data + sizeof(sctp_addiphdr_t);
+		if (param.p->type != SCTP_PARAM_IPV4_ADDRESS &&
+		    param.p->type != SCTP_PARAM_IPV6_ADDRESS)
+			return false;
+	}
 	if (param.v != chunk->chunk_end)
 		return false;
 
-- 
2.1.0

Re: [PATCH net v2] sctp: asconf's process should verify address parameter is in the beginning

[Marcelo Ricardo Leitner]

On Tue, Aug 25, 2015 at 08:29:24PM +0800, Xin Long wrote:
> in sctp_process_asconf(), we get address parameter from the beginning of
> the addip params. but we never check if it's really there. if the addr
> param is not there, it still can pass sctp_verify_asconf(), then to be
> handled by sctp_process_asconf(), it will not be safe.
> 
> so add a code in sctp_verify_asconf() to check the address parameter is in
> the beginning, or return false to send abort.
> 
> v1->v2:
>  * put the check behind the params' length verify.
> 
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  net/sctp/sm_make_chunk.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> index 06320c8..89a4d1c 100644
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -3166,6 +3166,13 @@ bool sctp_verify_asconf(const struct sctp_association *asoc,
>  		return false;
>  	if (!addr_param_needed && addr_param_seen)
>  		return false;
> +	if (addr_param_needed && addr_param_seen) {
> +		/* Ensure the address parameter is in the beginning */
> +		param.v = chunk->skb->data + sizeof(sctp_addiphdr_t);

Using param.v before the loop made sense but after the loop, it will
cause all packets that hits here to be reject due to the check below.

> +		if (param.p->type != SCTP_PARAM_IPV4_ADDRESS &&
> +		    param.p->type != SCTP_PARAM_IPV6_ADDRESS)
> +			return false;
> +	}
>  	if (param.v != chunk->chunk_end)
   this one    -----^

Maybe it's easier if you put this check inside the loop for each ipv4/6,
and check if it is the first parameter or not by mimicing the way
sctp_walk_params() finds the first chunk, it's just a pointer
derreference and that was already checked and performed to reach there.

(You can have some logic with addr_param_seen so you don't catch the
multiple parameters in there.)

  Marcelo

>  		return false;
>  
> -- 
> 2.1.0
> 

Re: [PATCH net v2] sctp: asconf's process should verify address parameter is in the beginning

[Vlad Yasevich]

On 08/25/2015 10:01 AM, Marcelo Ricardo Leitner wrote:
> On Tue, Aug 25, 2015 at 08:29:24PM +0800, Xin Long wrote:
>> in sctp_process_asconf(), we get address parameter from the beginning of
>> the addip params. but we never check if it's really there. if the addr
>> param is not there, it still can pass sctp_verify_asconf(), then to be
>> handled by sctp_process_asconf(), it will not be safe.
>>
>> so add a code in sctp_verify_asconf() to check the address parameter is in
>> the beginning, or return false to send abort.
>>
>> v1->v2:
>>  * put the check behind the params' length verify.
>>
>> Signed-off-by: Xin Long <lucien.xin@gmail.com>
>> ---
>>  net/sctp/sm_make_chunk.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
>> index 06320c8..89a4d1c 100644
>> --- a/net/sctp/sm_make_chunk.c
>> +++ b/net/sctp/sm_make_chunk.c
>> @@ -3166,6 +3166,13 @@ bool sctp_verify_asconf(const struct sctp_association *asoc,
>>  		return false;
>>  	if (!addr_param_needed && addr_param_seen)
>>  		return false;
>> +	if (addr_param_needed && addr_param_seen) {
>> +		/* Ensure the address parameter is in the beginning */
>> +		param.v = chunk->skb->data + sizeof(sctp_addiphdr_t);
> 
> Using param.v before the loop made sense but after the loop, it will
> cause all packets that hits here to be reject due to the check below.
> 
>> +		if (param.p->type != SCTP_PARAM_IPV4_ADDRESS &&
>> +		    param.p->type != SCTP_PARAM_IPV6_ADDRESS)
>> +			return false;
>> +	}
>>  	if (param.v != chunk->chunk_end)
>    this one    -----^
> 
> Maybe it's easier if you put this check inside the loop for each ipv4/6,
> and check if it is the first parameter or not by mimicing the way
> sctp_walk_params() finds the first chunk, it's just a pointer
> derreference and that was already checked and performed to reach there.
> 
> (You can have some logic with addr_param_seen so you don't catch the
> multiple parameters in there.)

Exactly!

something like this:
	SCTP_PARAM_IPV4_ADDRESS:
		if (param.v == addip->addip_hdr.params)
			addr_param_seen = true;

Thus making sure that the parameter as seen only when it's at the beginning...

Then later we can do things like:
	SCTP_PARAM_IPV4_ADDRESS:
		if (addr_param_seen) {
			/* peer placed multiple address parameters into the same
			 * asconf. reject it.
			 */
			return false;
		}

-vlad


> 
>   Marcelo
> 
>>  		return false;
>>  
>> -- 
>> 2.1.0
>>