linux-kernel - Re: memory leak in sctp_process

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Date:   Thu, 30 May 2019 12:17:05 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Neil Horman <nhorman@...driver.com>
Cc:     syzbot <syzbot+f7e9153b037eac9b1df8@...kaller.appspotmail.com>,
        davem@...emloft.net, linux-kernel@...r.kernel.org,
        linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, vyasevich@...il.com
Subject: Re: memory leak in sctp_process_init

On Thu, May 30, 2019 at 10:20:11AM -0400, Neil Horman wrote:
> On Wed, May 29, 2019 at 08:37:57PM -0300, Marcelo Ricardo Leitner wrote:
> > On Wed, May 29, 2019 at 03:07:09PM -0400, Neil Horman wrote:
> > > --- a/net/sctp/sm_make_chunk.c
> > > +++ b/net/sctp/sm_make_chunk.c
> > > @@ -2419,9 +2419,12 @@ int sctp_process_init(struct sctp_association *asoc, struct sctp_chunk *chunk,
> > >  	/* Copy cookie in case we need to resend COOKIE-ECHO. */
> > >  	cookie = asoc->peer.cookie;
> > >  	if (cookie) {
> > > +		if (asoc->peer.cookie_allocated)
> > > +			kfree(cookie);
> > >  		asoc->peer.cookie = kmemdup(cookie, asoc->peer.cookie_len, gfp);
> > >  		if (!asoc->peer.cookie)
> > >  			goto clean_up;
> > > +		asoc->peer.cookie_allocated=1;
> > >  	}
> > >  
> > >  	/* RFC 2960 7.2.1 The initial value of ssthresh MAY be arbitrarily
> > 
> > What if we kmemdup directly at sctp_process_param(), as it's done for
> > others already? Like SCTP_PARAM_RANDOM and SCTP_PARAM_HMAC_ALGO. I
> > don't see a reason for SCTP_PARAM_STATE_COOKIE to be different
> > here. This way it would be always allocated, and ready to be kfreed.
> > 
> > We still need to free it after the handshake, btw.
> > 
> >   Marcelo
> > 
> 
> Still untested, but something like this?
> 

Yes, just..

> 
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index d2c7d0d2abc1..718b9917844e 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -393,6 +393,7 @@ void sctp_association_free(struct sctp_association *asoc)
>  	kfree(asoc->peer.peer_random);
>  	kfree(asoc->peer.peer_chunks);
>  	kfree(asoc->peer.peer_hmacs);
> +	kfree(asoc->peer.cookie);

this chunk is not needed because it is freed right above the first
kfree() in the context here.

>  
>  	/* Release the transport structures. */
>  	list_for_each_safe(pos, temp, &asoc->peer.transport_addr_list) {
> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> index 72e74503f9fc..ff365f22a3c1 100644
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -2431,14 +2431,6 @@ int sctp_process_init(struct sctp_association *asoc, struct sctp_chunk *chunk,
>  	/* Peer Rwnd   : Current calculated value of the peer's rwnd.  */
>  	asoc->peer.rwnd = asoc->peer.i.a_rwnd;
>  
> -	/* Copy cookie in case we need to resend COOKIE-ECHO. */
> -	cookie = asoc->peer.cookie;
> -	if (cookie) {
> -		asoc->peer.cookie = kmemdup(cookie, asoc->peer.cookie_len, gfp);
> -		if (!asoc->peer.cookie)
> -			goto clean_up;
> -	}
> -
>  	/* RFC 2960 7.2.1 The initial value of ssthresh MAY be arbitrarily
>  	 * high (for example, implementations MAY use the size of the receiver
>  	 * advertised window).
> @@ -2607,7 +2599,9 @@ 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);
> -		asoc->peer.cookie = param.cookie->body;
> +		asoc->peer.cookie = kmemdup(param.cookie->body, asoc->peer.cookie_len, gfp);
> +		if (!asoc->peer.cookie)
> +			retval = 0;
>  		break;
>  
>  	case SCTP_PARAM_HEARTBEAT_INFO:

Plus:

--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -898,6 +898,11 @@ static void sctp_cmd_new_state(struct sctp_cmd_seq *cmds,
 						asoc->rto_initial;
 	}
 
+	if (sctp_state(asoc, ESTABLISHED)) {
+		kfree(asoc->peer.cookie);
+		asoc->peer.cookie = NULL;
+	}
+
 	if (sctp_state(asoc, ESTABLISHED) ||
 	    sctp_state(asoc, CLOSED) ||
 	    sctp_state(asoc, SHUTDOWN_RECEIVED)) {

Also untested, just sharing the idea.

  Marcelo