From patchwork Thu Feb 27 12:58:41 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. 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R. Silva" To: Mimi Zohar , Dmitry Kasatkin , James Morris , "Serge E. Hallyn" Cc: linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH] security: integrity: Replace zero-length array with flexible-array member Message-ID: <20200227125841.GA23703@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4166.hostgator.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 201.166.157.75 X-Source-L: No X-Exim-ID: 1j7Ihh-000gWF-C4 X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: (embeddedor) [201.166.157.75]:39906 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 10 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva --- security/integrity/ima/ima.h | 2 +- security/integrity/integrity.h | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index 64317d95363e..da4246ee7e35 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -95,7 +95,7 @@ struct ima_template_entry { u8 digest[TPM_DIGEST_SIZE]; /* sha1 or md5 measurement hash */ struct ima_template_desc *template_desc; /* template descriptor */ u32 template_data_len; - struct ima_field_data template_data[0]; /* template related data */ + struct ima_field_data template_data[]; /* template related data */ }; struct ima_queue_entry { diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h index 543d277c7e48..3c7e8b902256 100644 --- a/security/integrity/integrity.h +++ b/security/integrity/integrity.h @@ -103,7 +103,7 @@ struct ima_digest_data { } ng; u8 data[2]; } xattr; - u8 digest[0]; + u8 digest[]; } __packed; /* @@ -115,7 +115,7 @@ struct signature_v2_hdr { uint8_t hash_algo; /* Digest algorithm [enum hash_algo] */ __be32 keyid; /* IMA key identifier - not X509/PGP specific */ __be16 sig_size; /* signature size */ - uint8_t sig[0]; /* signature payload */ + uint8_t sig[]; /* signature payload */ } __packed; /* integrity data associated with an inode */