linux-kernel - Re: [PATCH] apparmor: Replace zero-length array with flexible-array member

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Message-ID: <4c8bf961-1d0d-9a63-3b1b-3aa6acb55179@embeddedor.com>
Date:   Thu, 27 Feb 2020 06:53:44 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>
Cc:     linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] apparmor: Replace zero-length array with flexible-array
 member

Hi all,

Friendly ping: Who can take this?

Thanks
--
Gustavo

On 2/11/20 15:04, Gustavo A. R. Silva 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
> inadvertenly introduced[3] to the codebase from now on.
> 
> 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 <gustavo@...eddedor.com>
> ---
>  security/apparmor/apparmorfs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
> index fefee040bf79..cc81080efb63 100644
> --- a/security/apparmor/apparmorfs.c
> +++ b/security/apparmor/apparmorfs.c
> @@ -804,7 +804,7 @@ static ssize_t query_label(char *buf, size_t buf_len,
>  struct multi_transaction {
>  	struct kref count;
>  	ssize_t size;
> -	char data[0];
> +	char data[];
>  };
>  
>  #define MULTI_TRANSACTION_LIMIT (PAGE_SIZE - sizeof(struct multi_transaction))
>