linux-hardening - Re: [PATCH] wifi: p54: Annotate struct p54_cal_database with __counted

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Date: Mon, 9 Oct 2023 09:07:17 -0700
From: Kees Cook <keescook@...omium.org>
To: Jason Andryuk <jandryuk@...il.com>
Cc: Christian Lamparter <chunkeey@...glemail.com>,
	Kalle Valo <kvalo@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-wireless@...r.kernel.org, linux-hardening@...r.kernel.org,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: Re: [PATCH] wifi: p54: Annotate struct p54_cal_database with
 __counted_by

On Mon, Oct 09, 2023 at 10:55:32AM -0400, Jason Andryuk wrote:
> Hi,
> 
> I randomly peeked at this patch.  Unfortunately, I am not familiar
> with the actual p54 code.
> 
> On Fri, Oct 6, 2023 at 4:17 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > attribute. Flexible array members annotated with __counted_by can have
> > their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> > array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > functions).
> >
> > As found with Coccinelle[1], add __counted_by for struct p54_cal_database.
> >
> > Cc: Christian Lamparter <chunkeey@...glemail.com>
> > Cc: Kalle Valo <kvalo@...nel.org>
> > Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> > Cc: linux-wireless@...r.kernel.org
> > Cc: linux-hardening@...r.kernel.org
> > Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> >  drivers/net/wireless/intersil/p54/p54.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/wireless/intersil/p54/p54.h b/drivers/net/wireless/intersil/p54/p54.h
> > index 3356ea708d81..770e348d1f6c 100644
> > --- a/drivers/net/wireless/intersil/p54/p54.h
> > +++ b/drivers/net/wireless/intersil/p54/p54.h
> > @@ -126,7 +126,7 @@ struct p54_cal_database {
> >         size_t entry_size;
> >         size_t offset;
> >         size_t len;
> > -       u8 data[];
> > +       u8 data[] __counted_by(entries);
> 
> This looks incorrect - I think you want __counted_by(len)?  The
> presence of entry_size made me suspicious.
> 
> >  };
> 
> This is the function that creates struct p54_cal_database:
> 
> static struct p54_cal_database *p54_convert_db(struct pda_custom_wrapper *src,
>                                                size_t total_len)
> {
>         struct p54_cal_database *dst;
>         size_t payload_len, entries, entry_size, offset;
> 
>         payload_len = le16_to_cpu(src->len);
>         entries = le16_to_cpu(src->entries);
>         entry_size = le16_to_cpu(src->entry_size);
>         offset = le16_to_cpu(src->offset);
>         if (((entries * entry_size + offset) != payload_len) ||
>              (payload_len + sizeof(*src) != total_len))
>                 return NULL;
> 
>         dst = kmalloc(sizeof(*dst) + payload_len, GFP_KERNEL);
>         if (!dst)
>                 return NULL;
> 
>         dst->entries = entries;
>         dst->entry_size = entry_size;
>         dst->offset = offset;
>         dst->len = payload_len;
> 
>         memcpy(dst->data, src->data, payload_len);
>         return dst;
> }
> 
> You can see that kmalloc is performed with `sizeof(*dst) +
> payload_len`, and payload_len is assigned to ->len.

Agreed!

> I don't read Coccinelle, but, if this patch was auto-generated, I
> wonder if the script has an error.

Yeah, I'm not sure which part went wrong. I will investigate. Thanks for
catching this!

-- 
Kees Cook