linux-kernel - Re: [PATCH] drm: amdgpu: Use the correct size when allocating memory

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Date:   Tue, 11 Aug 2020 10:57:02 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Marion & Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     alexander.deucher@....com, christian.koenig@....com,
        airlied@...ux.ie, daniel@...ll.ch, sumit.semwal@...aro.org,
        colton.w.lewis@...tonmail.com, Ori.Messinger@....com,
        m.szyprowski@...sung.com, bernard@...o.com,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] drm: amdgpu: Use the correct size when allocating memory

On Mon, Aug 10, 2020 at 08:41:14PM +0200, Marion & Christophe JAILLET wrote:
> 
> Le 10/08/2020 à 17:42, Dan Carpenter a écrit :
> > On Sun, Aug 09, 2020 at 10:34:06PM +0200, Christophe JAILLET wrote:
> > > When '*sgt' is allocated, we must allocated 'sizeof(**sgt)' bytes instead
> > > of 'sizeof(*sg)'. 'sg' (i.e. struct scatterlist) is smaller than
> > > 'sgt' (i.e struct sg_table), so this could lead to memory corruption.
> > The sizeof(*sg) is bigger than sizeof(**sgt) so this wastes memory but
> > it won't lead to corruption.
> > 
> >      11  struct scatterlist {
> >      12          unsigned long   page_link;
> >      13          unsigned int    offset;
> >      14          unsigned int    length;
> >      15          dma_addr_t      dma_address;
> >      16  #ifdef CONFIG_NEED_SG_DMA_LENGTH
> >      17          unsigned int    dma_length;
> >      18  #endif
> >      19  };
> > 
> >      42  struct sg_table {
> >      43          struct scatterlist *sgl;        /* the list */
> >      44          unsigned int nents;             /* number of mapped entries */
> >      45          unsigned int orig_nents;        /* original size of list */
> >      46  };
> > 
> > regards,
> > dan carpenter
> 
> 
> My bad. I read 'struct scatterlist sgl' (without the *)
> Thanks for the follow-up, Dan.
> 
> Doesn't smatch catch such mismatch?
> (I've not run smatch for a while, so it is maybe reported)

That's why I was investigating it, because Smatch didn't catch it.

Smatch would have warned if it led to memory corruption.  Smatch also
tries to detect struct mismatches as a separate check but for some
reason it missed it.  I'm not totally sure why yet.  I suspect that it's
a complicated internal reason where Sparse is the sizeof to a normal
number...  It's a known issue and hard to fix.

> 
> Well, the proposal is still valid, even if it has less impact as initially
> thought.

Yep.

regards,
dan carpenter