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SubjectRe: [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@chromium.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@googlemail.com>
> > Cc: Kalle Valo <kvalo@kernel.org>
> > Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> > Cc: linux-wireless@vger.kernel.org
> > Cc: linux-hardening@vger.kernel.org
> > Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> > Signed-off-by: Kees Cook <keescook@chromium.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

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