linux-hardening - Re: [PATCH v5][next] integrity: Avoid -Wflex-array-member-not-at-end warnings

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Thu, 04 Apr 2024 12:49:53 -0400
From: Mimi Zohar <zohar@...ux.ibm.com>
To: "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
Subject: Re: [PATCH v5][next] integrity: Avoid
 -Wflex-array-member-not-at-end warnings

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@...nel.org>

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

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

Mimi