linux-kernel - Re: [PATCH 01/11] media: tm6000: fix potential Spectre variant 1

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Date:   Wed, 16 May 2018 10:36:56 -0300
From:   Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/11] media: tm6000: fix potential Spectre variant 1

Em Wed, 16 May 2018 16:11:08 +0300
Dan Carpenter <dan.carpenter@...cle.com> escreveu:

> On Tue, May 15, 2018 at 04:00:33PM -0300, Mauro Carvalho Chehab wrote:
> > Yeah, that's the same I'm getting from media upstream.
> >   
> > > drivers/media/cec/cec-pin-error-inj.c:170 cec_pin_error_inj_parse_line() 
> > > warn: potential spectre issue 'pin->error_inj_args'  
> > 
> > This one seems a false positive, as the index var is u8 and the
> > array has 256 elements, as the userspace input from 'op' is 
> > initialized with:
> > 
> > 	u8 v;
> > 	u32 op;
> > 
> > 	if (!kstrtou8(token, 0, &v))
> > 		op = v;
> >   
> 
> It's hard to silence this because Smatch stores the current user
> controlled range list, not what it was initially.  I wrote all this code
> to detect bounds checking errors, so there wasn't any need to save the
> range list before the bounds check.  Since "op" is a u32, I can't even
> go by the type of the index....

Yeah, I was thinking that is would be harder to clean this up on
smatch. I proposed a patch to the ML that simplifies the logic,
making easier for both humans and Smatch to better understand how
the arrays are indexed.

> 
> > > drivers/media/dvb-core/dvb_ca_en50221.c:1479 dvb_ca_en50221_io_write() 
> > > warn: potential spectre issue 'ca->slot_info' (local cap)  
> > 
> > This one seems a real issue to me. Sent a patch for it.
> >   
> > > drivers/media/dvb-core/dvb_net.c:252 handle_one_ule_extension() warn: 
> > > potential spectre issue 'p->ule_next_hdr'  
> > 
> > I failed to see what's wrong here, or if this is exploited.   
> 
> Oh...  Huh.  This is a bug in smatch.  That line looks like:
> 
> 	p->ule_sndu_type = ntohs(*(__be16 *)(p->ule_next_hdr + ((p->ule_dbit ? 2 : 3) * ETH_ALEN)));
> 
> Smatch see the ntohs() and marks everything inside it as untrusted
> network data.  I'll fix this.

Thanks!

Regards,
Mauro