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List:       linux-hardening
Subject:    Re: [PATCH 2/2][next] media: staging/intel-ipu3: css: Replace one-element array and use struct_size(
From:       "Gustavo A. R. Silva" <gustavoars () kernel ! org>
Date:       2021-07-30 8:40:09
Message-ID: 20210730084009.GA5422 () embeddedor
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On Fri, Jul 30, 2021 at 10:49:50AM +0300, Dan Carpenter wrote:
> On Thu, Jul 29, 2021 at 06:22:40PM -0500, Gustavo A. R. Silva wrote:
> > There is a regular need in the kernel to provide a way to declare having
> > a dynamically sized set of trailing elements in a structure. Kernel code
> > should always use "flexible array members"[1] for these cases. The older
> > style of one-element or zero-length arrays should no longer be used[2].
> > 
> > Replace a one-element array with a flexible-array member in struct
> > imgu_fw_header and use the struct_size() helper.
> > 
> > This also helps with the ongoing efforts to globally enable
> > -Warray-bounds and get us closer to being able to tighten the
> > FORTIFY_SOURCE routines on memcpy().
> > 
> > [1] https://en.wikipedia.org/wiki/Flexible_array_member
> > [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
> > 
> > Link: https://github.com/KSPP/linux/issues/79
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > ---
> >  drivers/staging/media/ipu3/ipu3-css-fw.c | 5 ++---
> >  drivers/staging/media/ipu3/ipu3-css-fw.h | 2 +-
> >  2 files changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/staging/media/ipu3/ipu3-css-fw.c b/drivers/staging/media/ipu3/ipu3-css-fw.c
> > index ab021afff954..3b7df1128840 100644
> > --- a/drivers/staging/media/ipu3/ipu3-css-fw.c
> > +++ b/drivers/staging/media/ipu3/ipu3-css-fw.c
> > @@ -127,9 +127,8 @@ int imgu_css_fw_init(struct imgu_css *css)
> >  	if (css->fw->size < sizeof(struct imgu_fw_header) ||
>                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Originally this was sizeof() the pointer which is clearly wrong.  Then
> patch 1 changed it to force that binary_header[] had at least one
> element, but now it's changed again to say that binary_header[] can have
> zero elements.  So either patch 1 or patch 2 is wrong.
> 
> I feel like the probably the correct fix is to just fold these two
> patches together and say that binary_header[] with zero elements is
> allowed.  But I don't know this code well.

Oops... I forgot to tag this one for stable, too. But it would probably
be better to fold both of these into a single patch as you suggest.

To me these two pieces of code suggest that binary_header[] should not
be declared as a one-element array, but a flexible one instead:

130                 if (sizeof(struct imgu_fw_bi_file_h) +
131                     css->fwp->file_header.binary_nr * sizeof(struct imgu_fw_info) >
132                     css->fw->size)
133                         goto bad_fw;
...
147                 for (i = 0; i < binary_nr; i++) {
148                         struct imgu_fw_info *bi = &css->fwp->binary_header[i];
...

Thanks
--
Gustavo
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