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Message-ID: <fe36683b-ec78-4f83-b4ad-8dca35e4fa09@embeddedor.com>
Date: Wed, 20 Mar 2024 21:39:32 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Mimi Zohar <zohar@...ux.ibm.com>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>,
Roberto Sassu <roberto.sassu@...wei.com>,
Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
Eric Snowberg <eric.snowberg@...cle.com>, Paul Moore <paul@...l-moore.com>,
James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>
Cc: linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH][next] integrity: Avoid -Wflex-array-member-not-at-end
warnings
On 20/03/24 19:19, Mimi Zohar wrote:
> Hi Gustavo,
>
> Sorry for the delay...
No worries. :)
>
> On Mon, 2024-03-04 at 11:52 -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 another struct, we use the `struct_group_tagged()` helper to
>> separate the flexible array from the rest of the members in the flexible
>> structure:
>>
>> struct ima_digest_data {
>> struct_group_tagged(ima_digest_data_hdr, hdr,
>>
>> ... 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, 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;
>>
>> We also use `container_of()` whenever we need to retrieve a pointer to
>> the flexible structure.
>
> Nice!
>
>>
>> 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]
>
> A similar change would need to be made to struct evm_digest:
>
> struct evm_digest {
> struct ima_digest_data hdr;
> char digest[IMA_MAX_DIGEST_SIZE];
> } __packed;
>
> Is there are another patch?
Oh, I missed that one. I'll include it and send v2, shortly.
Thanks!
--
Gustavo
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