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

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Message-ID: <CAKf6xptEEHJAsrwh_oebK1_AMb+_tvLtiY8sP-Qk=Z9jXhVf7Q@mail.gmail.com>
Date: Mon, 9 Oct 2023 10:55:32 -0400
From: Jason Andryuk <jandryuk@...il.com>
To: Kees Cook <keescook@...omium.org>
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

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.

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

Regards,
Jason