Re: [PATCH] wifi: p54: Annotate struct p54_cal_database with __counted_by

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 10/9/23 16:55, 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

I think you're right. More comments below...

> 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.

This should be changed to:

-       dst = kmalloc(sizeof(*dst) + payload_len, GFP_KERNEL);
+       dst = kmalloc(struct_size(dst, data, payload_len), GFP_KERNEL);

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

With the struct_size() change, the Coccinelle script should be able to
generate a correct patch for this.

--
Gustavo