Re: [PATCH] ti-st: fix NULL dereference on protocol type check

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Jul 25, 2013 at 07:16:28PM +0100, Gustavo Padovan wrote:
> * Andrew Morton <akpm@linux-foundation.org> [2013-07-24 16:12:22 -0700]:
> 
> > On Tue, 23 Jul 2013 15:29:31 +0100 Gustavo Padovan <gustavo@padovan.org> wrote:
> > 
> > > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > 
> > > If the type we receive is greater than ST_MAX_CHANNELS we can't rely on
> > > type as vector index since we would be accessing unknown memory when we use the type
> > > as index.
> > > 
> > >  Unable to handle kernel NULL pointer dereference at virtual address 0000001b
> > >  pgd = c0004000
> > >  [0000001b] *pgd=00000000
> > >  Internal error: Oops: 17 [#1] PREEMPT SMP ARM
> > >  Modules linked in: btwilink wl12xx wlcore mac80211 cfg80211 rfcomm bnep bluo
> > >  CPU: 0    Tainted: G        W     (3.4.0+ #15)
> > >  PC is at st_int_recv+0x278/0x344
> > >  LR is at get_parent_ip+0x14/0x30
> > >  pc : [<c03b01a8>]    lr : [<c007273c>]    psr: 200f0193
> > >  sp : dc631ed0  ip : e3e21c24  fp : dc631f04
> > >  r10: 00000000  r9 : 600f0113  r8 : 0000003f
> > >  r7 : e3e21b14  r6 : 00000067  r5 : e2e49c1c  r4 : e3e21a80
> > >  r3 : 00000001  r2 : 00000001  r1 : 00000001  r0 : 600f0113
> > >  Flags: nzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
> > >  Control: 10c5387d  Table: 9c50004a  DAC: 00000015
> > > 
> > > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > ---
> > >  drivers/misc/ti-st/st_core.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/misc/ti-st/st_core.c b/drivers/misc/ti-st/st_core.c
> > > index 0a14280..8e64eb1 100644
> > > --- a/drivers/misc/ti-st/st_core.c
> > > +++ b/drivers/misc/ti-st/st_core.c
> > > @@ -343,7 +343,7 @@ void st_int_recv(void *disc_data,
> > >  			/* Unknow packet? */
> > >  		default:
> > >  			type = *ptr;
> > > -			if (st_gdata->list[type] == NULL) {
> > > +			if (type >= ST_MAX_CHANNELS || st_gdata->list[type] == NULL) {
> > >  				pr_err("chip/interface misbehavior dropping"
> > >  					" frame starting with 0x%02x", type);
> > >  				goto done;
> > 
> > This would be a bug in the calling code, would it not?
> 
> It is possible and it seems 39f610e40 could be a fix for this. I would need to
> test. I was testing it on old kernel without this patch. In any case my patch
> is still needed.

Why?  Shouldn't you just prevent this from ever happening in the first
place?

thanks,

greg k-h