Subject: Re: [PATCH v5] net: caif: fix stack out-of-bounds write in cfctrl_link_setup()

From: Simon Horman <[email-masked]>
Date: Tue, 14 Apr 2026 12:29:51 +0100

On Mon, Apr 13, 2026 at 11:30:53AM +0200, Paolo Abeni wrote:
> On 4/12/26 3:57 PM, Simon Horman wrote:
> > I am wondering if it would be best to follow the pattern for
> > writing linkparam.u.utility.name elsewhere in this function.
> > That:
> > 1. Uses a somewhat more succinct loop control structure
> > 2. Silently truncates input without updating cmdrsp if overrun would occur
> > 
> > Something like this (compile tested only!):
> > 
> > diff --git a/net/caif/cfctrl.c b/net/caif/cfctrl.c
> > index c6cc2bfed65d..ba184c11386e 100644
> > --- a/net/caif/cfctrl.c
> > +++ b/net/caif/cfctrl.c
> > @@ -15,6 +15,7 @@
> >  #include <net/caif/cfctrl.h>
> >  
> >  #define container_obj(layr) container_of(layr, struct cfctrl, serv.layer)
> > +#define RFM_VOLUME_LEN 20
> >  #define UTILITY_NAME_LENGTH 16
> >  #define CFPKT_CTRL_PKT_LEN 20
> >  
> > @@ -414,10 +415,11 @@ static int cfctrl_link_setup(struct cfctrl *cfctrl, struct cfpkt *pkt, u8 cmdrsp
> >  		 */
> >  		linkparam.u.rfm.connid = cfpkt_extr_head_u32(pkt);
> >  		cp = (u8 *) linkparam.u.rfm.volume;
> > -		for (tmp = cfpkt_extr_head_u8(pkt);
> > -		     cfpkt_more(pkt) && tmp != '\0';
> > -		     tmp = cfpkt_extr_head_u8(pkt))
> > +		caif_assert(sizeof(linkparam.u.rfm.volume) >= RFM_VOLUME_LEN);
> > +		for(i = 0; i < RFM_VOLUME_LEN - 1 && cfpkt_more(pkt); i++) {
> > +			tmp = cfpkt_extr_head_u8(pkt);
> >  			*cp++ = tmp;
> > +		}
> >  		*cp = '\0';
> >  
> >  		if (CFCTRL_ERR_BIT & cmdrsp)
> 
> I agree that the code suggested by Simon is clearer. Note that AFAICS it
> lacks an additional `tmp!= '\0'` check to break the loop, but even with
> that added it should be preferable.

Sorry, I left out the `tmp!= '\0' check.
That was unintentional and I agree it should be there.