linux-kernel - Re: [PATCH] drm/nouveau: Use kmemdup

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Message-ID: <ba70e0f2-c957-4235-aa51-b1a8c86034b6@moroto.mountain>
Date: Tue, 18 Jun 2024 10:00:23 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Danilo Krummrich <dakr@...hat.com>
Cc: Lyude Paul <lyude@...hat.com>, David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>, dri-devel@...ts.freedesktop.org,
	nouveau@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org, Karol Herbst <kherbst@...hat.com>
Subject: Re: [PATCH] drm/nouveau: Use kmemdup_array() instead of kmemdup()

On Mon, Jun 17, 2024 at 05:55:33PM +0200, Danilo Krummrich wrote:
> On 6/17/24 11:33, Dan Carpenter wrote:
> > Use kmemdup_array() because we're allocating an array.
> > 
> > The main difference between kmemdup() and kmemdup_array() is that the
> > kmemdup_array() function has integer overflow checking built it.  The
> > "args->in_sync.count" variable is a u32 so integer overflows would only
> > be a concern on 32bit systems.  Fortunately, however, the u_memcpya()
> > function has integer overflow checking which means that it is not an
> > issue.
> > 
> > Still using kmemdup_array() is more appropriate and makes auditing the
> > code easier.
> 
> Indeed, we shouldn't rely on the previous check here, good catch.
> 
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> > ---
> >   drivers/gpu/drm/nouveau/nouveau_sched.c | 16 ++++++++--------
> >   1 file changed, 8 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_sched.c b/drivers/gpu/drm/nouveau/nouveau_sched.c
> > index 32fa2e273965..53d8b0584a56 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_sched.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_sched.c
> > @@ -45,10 +45,10 @@ nouveau_job_init(struct nouveau_job *job,
> >   		if (job->sync)
> >   			return -EINVAL;
> > -		job->in_sync.data = kmemdup(args->in_sync.s,
> > -					 sizeof(*args->in_sync.s) *
> > -					 args->in_sync.count,
> > -					 GFP_KERNEL);
> > +		job->in_sync.data = kmemdup_array(args->in_sync.s,
> > +					args->in_sync.count,
> > +					sizeof(*args->in_sync.s),
> > +					GFP_KERNEL);
> >   		if (!job->in_sync.data)
> >   			return -ENOMEM;
> 
> Not sure if this is what we want for kmemdup_array(). It just saturates the
> size. This doesn't prevent accessing the array out of bounds later on. I mean,
> it's rather unlikely to get such a huge amount of physically contiguous memory
> anyways, but wouldn't it be cleaner to let kmemdup_array() return
> ERR_PTR(-EOVERFLOW) on overflow, just like memdup_array_user()[1]?
> 
> AFAICS, there's just two users of kmemdup_array(), hence it should be an easy
> change. :-)
> 
> [1] https://elixir.bootlin.com/linux/latest/source/include/linux/string.h#L30
> 

We can't change the return values.

kmemdup_array() has to match kmemdup().  <-- returns NULL
memdup_array_user() has to match memdup_user().  <-- returns error pointer

regards,
dan carpenter