linux-kernel - Re: stm class: Prevent user-controllable allocations

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Message-ID: <20190507151108.GA16767@amd>
Date:   Tue, 7 May 2019 17:11:08 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Pavel Machek <pavel@...x.de>, alexander.shishkin@...ux.intel.com,
        security@...nel.org, sasha.levin@...cle.com,
        gregkh@...uxfoundation.org,
        kernel list <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...l.org>, trivial@...nel.org
Subject: Re: stm class: Prevent user-controllable allocations

On Tue 2019-05-07 15:50:27, Dan Carpenter wrote:
> On Tue, May 07, 2019 at 02:41:13PM +0200, Pavel Machek wrote:
> > 
> > It seems to me that we still allow overflow if count == ~0. We'll then
> > allocate 0 bytes but copy ~0 bytes. That does not sound healthy.
> > 
> > Fixes: f08b18266c7116e2ec6885dd53a928f580060a71
> > 
> > Signed-off-by: Pavel Machek <pavel@...x.de>
> > 
> > diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
> > index c7ba8ac..8846fca 100644
> > --- a/drivers/hwtracing/stm/core.c
> > +++ b/drivers/hwtracing/stm/core.c
> > @@ -631,7 +631,7 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
> >  	char *kbuf;
> >  	int err;
> >  
> > -	if (count + 1 > PAGE_SIZE)
> > +	if (count > PAGE_SIZE - 1)
> >  		count = PAGE_SIZE - 1;
> 
> The "count" variable should all be checked in vfs_write().  count + off
> is checked in rw_verify_area() and count is capped at MAX_RW_COUNT.
> 
> #define MAX_RW_COUNT (INT_MAX & PAGE_MASK)

Ok, so overflow is checked elsewhere. I'd still like patch to be
applied as it makes code more obvious.

Thanks,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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