linux-ext4 - Re: [PATCH] ext4: Annotate struct ext4_xattr_inode_array with __counted

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Message-ID: <db367563-e144-4a2f-8d67-d1b4e879397e@embeddedor.com>
Date: Mon, 29 Jul 2024 08:09:40 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Thorsten Blum <thorsten.blum@...lux.com>, tytso@....edu,
 adilger.kernel@...ger.ca, kees@...nel.org, gustavoars@...nel.org
Cc: linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ext4: Annotate struct ext4_xattr_inode_array with
 __counted_by()

On 29/07/24 05:04, Thorsten Blum wrote:
> Add the __counted_by compiler attribute to the flexible array member
> inodes to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.

This change seems to be incomplete. The relationship between `count` and
accesses to `inodes` should be adjusted at least in `ext4_expand_inode_array()`

See this for more details:

https://embeddedor.com/blog/2024/06/18/how-to-use-the-new-counted_by-attribute-in-c-and-linux/

Thanks
--
Gustavo

> 
> Remove the now obsolete comment on the count field.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@...lux.com>
> ---
>   fs/ext4/xattr.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
> index bd97c4aa8177..e14fb19dc912 100644
> --- a/fs/ext4/xattr.h
> +++ b/fs/ext4/xattr.h
> @@ -130,8 +130,8 @@ struct ext4_xattr_ibody_find {
>   };
>   
>   struct ext4_xattr_inode_array {
> -	unsigned int count;		/* # of used items in the array */
> -	struct inode *inodes[];
> +	unsigned int count;
> +	struct inode *inodes[] __counted_by(count);
>   };
>   
>   extern const struct xattr_handler ext4_xattr_user_handler;