[v2,net] Free cookie before we memdup a new one

Based on comments from Xin, even after fixes for our recent syzbot
report of cookie memory leaks, its possible to get a resend of an INIT
chunk which would lead to us leaking cookie memory.

To ensure that we don't leak cookie memory, free any previously
allocated cookie first.

---
Change notes
v1->v2
update subsystem tag in subject (davem)
repeat kfree check for peer_random and peer_hmacs (xin)

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
CC: Xin Long <lucien.xin@gmail.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: netdev@vger.kernel.org
---
 net/sctp/sm_make_chunk.c | 6 ++++++
 1 file changed, 6 insertions(+)

On Tue, Jun 11, 2019 at 07:21:28AM -0400, Neil Horman wrote:
> Based on comments from Xin, even after fixes for our recent syzbot
> report of cookie memory leaks, its possible to get a resend of an INIT
> chunk which would lead to us leaking cookie memory.
> 
> To ensure that we don't leak cookie memory, free any previously
> allocated cookie first.
> 
> ---
> Change notes
> v1->v2
> update subsystem tag in subject (davem)
> repeat kfree check for peer_random and peer_hmacs (xin)

They are actually 4 vars. The 4th one being peer_chunks.
And a syzkaller Fixes tag would be welcomed as well, so that if
someone backports the fix for it will have a hint to backport this
patch also.

> 
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> CC: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> CC: Xin Long <lucien.xin@gmail.com>
> CC: "David S. Miller" <davem@davemloft.net>
> CC: netdev@vger.kernel.org
> ---
>  net/sctp/sm_make_chunk.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> index f17908f5c4f3..0992ec0395f8 100644
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -2583,6 +2583,8 @@ static int sctp_process_param(struct sctp_association *asoc,
>  	case SCTP_PARAM_STATE_COOKIE:
>  		asoc->peer.cookie_len =
>  			ntohs(param.p->length) - sizeof(struct sctp_paramhdr);
> +		if (asoc->peer.cookie)
> +			kfree(asoc->peer.cookie);
>  		asoc->peer.cookie = kmemdup(param.cookie->body, asoc->peer.cookie_len, gfp);
>  		if (!asoc->peer.cookie)
>  			retval = 0;
> @@ -2647,6 +2649,8 @@ static int sctp_process_param(struct sctp_association *asoc,
>  			goto fall_through;
>  
>  		/* Save peer's random parameter */
> +		if (asoc->peer.peer_random)
> +			kfree(asoc->peer.peer_random);
>  		asoc->peer.peer_random = kmemdup(param.p,
>  					    ntohs(param.p->length), gfp);
>  		if (!asoc->peer.peer_random) {
> @@ -2660,6 +2664,8 @@ static int sctp_process_param(struct sctp_association *asoc,
>  			goto fall_through;
>  
>  		/* Save peer's HMAC list */
> +		if (asoc->peer.peer_hmacs)
> +			kfree(asoc->peer.peer_hmacs);
>  		asoc->peer.peer_hmacs = kmemdup(param.p,
>  					    ntohs(param.p->length), gfp);
>  		if (!asoc->peer.peer_hmacs) {
> -- 
> 2.20.1
>

On Tue, Jun 11, 2019 at 07:21:28AM -0400, Neil Horman wrote:

Btw, I guess DaveM had meant to add "sctp: " in the subject.

  Marcelo

From: Neil Horman <nhorman@tuxdriver.com>
Date: Tue, 11 Jun 2019 07:21:28 -0400

> Based on comments from Xin, even after fixes for our recent syzbot
> report of cookie memory leaks, its possible to get a resend of an INIT
> chunk which would lead to us leaking cookie memory.
> 
> To ensure that we don't leak cookie memory, free any previously
> allocated cookie first.
> 
> ---
> Change notes
> v1->v2
> update subsystem tag in subject (davem)

Subsystem tag is "sctp: " which still isn't there :-)