From: Paul Moore <paul@paul-moore.com>
To: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Eric Paris <eparis@redhat.com>,
linux-audit@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] audit: Replace zero-length array with flexible-array
Date: Thu, 7 May 2020 22:52:09 -0400 [thread overview]
Message-ID: <CAHC9VhSm_GWWXuzuwrrcTF3QcKCv1WSZv2=WF4t3DB4P7vshoA@mail.gmail.com> (raw)
In-Reply-To: <20200507185041.GA13930@embeddedor>
On Thu, May 7, 2020 at 2:46 PM Gustavo A. R. Silva
<gustavoars@kernel.org> wrote:
> 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]
>
> sizeof(flexible-array-member) triggers a warning because flexible array
> members have incomplete type[1]. There are some instances of code in
> which the sizeof operator is being incorrectly/erroneously applied to
> zero-length arrays and the result is zero. Such instances may be hiding
> some bugs. So, this work (flexible-array member conversions) will also
> help to get completely rid of those sorts of issues.
>
> 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 <gustavoars@kernel.org>
> ---
> include/linux/audit.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Merged into audit/next, thanks!
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index f9ceae57ca8d..2b63aee6e9fa 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -19,7 +19,7 @@
> struct audit_sig_info {
> uid_t uid;
> pid_t pid;
> - char ctx[0];
> + char ctx[];
> };
>
> struct audit_buffer;
--
paul moore
www.paul-moore.com
next prev parent reply other threads:[~2020-05-08 2:52 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-07 18:50 [PATCH] audit: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-07 21:58 ` Richard Guy Briggs
2020-05-07 22:49 ` Gustavo A. R. Silva
2020-05-08 2:48 ` Paul Moore
2020-05-08 11:17 ` Richard Guy Briggs
2020-05-08 2:52 ` Paul Moore [this message]
2020-05-08 23:51 ` Gustavo A. R. Silva
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