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Message-ID: <27d36ec8e0539c5d6bc760de7305299a2142f9f1.camel@linux.ibm.com>
Subject: Re: [PATCH v5][next] integrity: Avoid
 -Wflex-array-member-not-at-end warnings
From: Mimi Zohar <zohar@linux.ibm.com>
To: "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Roberto Sassu
 <roberto.sassu@huawei.com>,
        Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
        Eric Snowberg <eric.snowberg@oracle.com>,
        Paul Moore <paul@paul-moore.com>, James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Date: Thu, 04 Apr 2024 12:49:53 -0400
In-Reply-To: <Zg7AoOh7CL5ZD/fe@neat>
References: <Zg7AoOh7CL5ZD/fe@neat>
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Hi Gustavo,

On Thu, 2024-04-04 at 09:00 -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;
> 
> And similarly for `struct evm_ima_xattr_data`.
> 
> 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` and `struct evm_xattr`.
> 
> 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:64:32: warning: structure containing a flexible
> array member is not at the end of another structure [-Wflex-array-member-not-
> at-end]
> security/integrity/evm/../integrity.h:40:35: warning: structure containing a
> flexible array member is not at the end of another structure [-Wflex-array-
> member-not-at-end]
> security/integrity/evm/../integrity.h:68:32: warning: structure containing a
> flexible array member is not at the end of another structure [-Wflex-array-
> member-not-at-end]
> security/integrity/ima/../integrity.h:40:35: warning: structure containing a
> flexible array member is not at the end of another structure [-Wflex-array-
> member-not-at-end]
> security/integrity/ima/../integrity.h:68:32: warning: structure containing a
> flexible array member is not at the end of another structure [-Wflex-array-
> member-not-at-end]
> security/integrity/integrity.h:40:35: warning: structure containing a flexible
> array member is not at the end of another structure [-Wflex-array-member-not-
> at-end]
> security/integrity/integrity.h:68:32: warning: structure containing a flexible
> array member is not at the end of another structure [-Wflex-array-member-not-
> at-end]
> security/integrity/platform_certs/../integrity.h:40:35: warning: structure
> containing a flexible array member is not at the end of another structure [-
> Wflex-array-member-not-at-end]
> security/integrity/platform_certs/../integrity.h:68:32: warning: structure
> containing a flexible array member is not at the end of another structure [-
> Wflex-array-member-not-at-end]
> 
> Link: https://github.com/KSPP/linux/issues/202
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>

Thanks, Gustavo.  I already applied and tested v4, but was trying to actually
see the errors with before pushing it out.

Mimi