linux-kernel - Re: memory leak in sctp_process

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Date:   Thu, 30 May 2019 15:56:34 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.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 12:17:05PM -0300, Marcelo Ricardo Leitner wrote:
> 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.
> 
Ah, thanks, missed that.

> >  
> >  	/* 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;
> +	}
> +
Not sure I follow why this is needed.  It doesn't hurt anything of course, but
if we're freeing in sctp_association_free, we don't need to duplicate the
operation here, do we?
>  	if (sctp_state(asoc, ESTABLISHED) ||
>  	    sctp_state(asoc, CLOSED) ||
>  	    sctp_state(asoc, SHUTDOWN_RECEIVED)) {
> 
> Also untested, just sharing the idea.
> 
>   Marcelo
>