[PATCH v3][next] integrity: Avoid -Wflex-array-member-not-at-end warnings
Gustavo A. R. Silva
gustavo at embeddedor.com
Thu Mar 21 15:49:29 UTC 2024
On 3/21/24 07:58, Mimi Zohar wrote:
> On Wed, 2024-03-20 at 22:11 -0600, Gustavo A. R. Silva wrote:
>> -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
>> ready to enable it globally.
>>
>> There is currently an object (`hdr)` in `struct ima_max_digest_data`
>> that contains a flexible structure (`struct ima_digest_data`):
>>
>> struct ima_max_digest_data {
>> struct ima_digest_data hdr;
>> u8 digest[HASH_MAX_DIGESTSIZE];
>> } __packed;
>>
>> So, in order to avoid ending up with a flexible-array member in the
>> middle of a struct, we use the `__struct_group()` helper to separate
>> the flexible array from the rest of the members in the flexible
>> structure:
>>
>> struct ima_digest_data {
>> __struct_group(ima_digest_data_hdr, hdr, __packed,
>>
>> ... the rest of the members
>>
>> );
>> u8 digest[];
>> } __packed;
>>
>> With the change described above, we can now declare an object of the
>> type of the tagged `struct ima_digest_data_hdr`, without embedding the
>> flexible array in the middle of another struct:
>>
>> struct ima_max_digest_data {
>> struct ima_digest_data_hdr hdr;
>> u8 digest[HASH_MAX_DIGESTSIZE];
>> } __packed;
>>
>
> And similarly for 'struct evm_digest'.
Yes. :)
>
>
>> We also use `container_of()` whenever we need to retrieve a pointer to
>> the flexible structure.
>>
>> So, with these changes, fix the following warnings:
>>
>> security/integrity/evm/evm.h:45:32: warning: structure containing a flexible
>> array member is not at the end of another structure [-Wflex-array-member-not-
>> at-end]
>> security/integrity/evm/evm.h:45:32: warning: structure containing a flexible
>> array member is not at the end of another structure [-Wflex-array-member-not-
>> at-end]
>> security/integrity/evm/evm.h:45:32: warning: structure containing a flexible
>> array member is not at the end of another structure [-Wflex-array-member-not-
>> at-end]
>
> I assume these messages are gone.
Yes. :)
Thanks
--
Gustavo
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