linux-hardening - Re: [PATCH][next] hpfs: Replace one-element array with flexible-array member

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Date:   Thu, 15 Apr 2021 14:54:31 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
Cc:     linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH][next] hpfs: Replace one-element array with flexible-array
 member

Hi all,

Friendly ping: who can take this, please?

Thanks
--
Gustavo

On 3/26/21 12:35, Gustavo A. R. Silva wrote:
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use “flexible array members”[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
> 
> Also, this helps with the ongoing efforts to enable -Warray-bounds by
> fixing the following warning:
> 
>   CC [M]  fs/hpfs/dir.o
> fs/hpfs/dir.c: In function ‘hpfs_readdir’:
> fs/hpfs/dir.c:163:41: warning: array subscript 1 is above array bounds of ‘u8[1]’ {aka ‘unsigned char[1]’} [-Warray-bounds]
>   163 |         || de ->name[0] != 1 || de->name[1] != 1))
>       |                                 ~~~~~~~~^~~
> 
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
> 
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/109
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  fs/hpfs/hpfs.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/hpfs/hpfs.h b/fs/hpfs/hpfs.h
> index 302f45101a96..d92c4af3e1b4 100644
> --- a/fs/hpfs/hpfs.h
> +++ b/fs/hpfs/hpfs.h
> @@ -356,7 +356,8 @@ struct hpfs_dirent {
>    u8 no_of_acls;			/* number of ACL's (low 3 bits) */
>    u8 ix;				/* code page index (of filename), see
>  					   struct code_page_data */
> -  u8 namelen, name[1];			/* file name */
> +  u8 namelen;				/* file name length */
> +  u8 name[];				/* file name */
>    /* dnode_secno down;	  btree down pointer, if present,
>       			  follows name on next word boundary, or maybe it
>  			  precedes next dirent, which is on a word boundary. */
>