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

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Message-ID: <20240917122529.lmikh56cfbjr3lsz@quack3>
Date: Tue, 17 Sep 2024 14:25:29 +0200
From: Jan Kara <jack@...e.cz>
To: Thorsten Blum <thorsten.blum@...lux.com>
Cc: tytso@....edu, adilger.kernel@...ger.ca, kees@...nel.org,
	gustavoars@...nel.org, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ext4: Annotate struct fname with __counted_by()

On Fri 13-09-24 13:00:14, Thorsten Blum wrote:
> Add the __counted_by compiler attribute to the flexible array member
> name to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.
> 
> Inline and use struct_size() to calculate the number of bytes to
> allocate for new_fn and remove the local variable len.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@...lux.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/dir.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
> index ff4514e4626b..8e7df15bb971 100644
> --- a/fs/ext4/dir.c
> +++ b/fs/ext4/dir.c
> @@ -408,7 +408,7 @@ struct fname {
>  	__u32		inode;
>  	__u8		name_len;
>  	__u8		file_type;
> -	char		name[];
> +	char		name[] __counted_by(name_len);
>  };
>  
>  /*
> @@ -464,14 +464,13 @@ int ext4_htree_store_dirent(struct file *dir_file, __u32 hash,
>  	struct rb_node **p, *parent = NULL;
>  	struct fname *fname, *new_fn;
>  	struct dir_private_info *info;
> -	int len;
>  
>  	info = dir_file->private_data;
>  	p = &info->root.rb_node;
>  
>  	/* Create and allocate the fname structure */
> -	len = sizeof(struct fname) + ent_name->len + 1;
> -	new_fn = kzalloc(len, GFP_KERNEL);
> +	new_fn = kzalloc(struct_size(new_fn, name, ent_name->len + 1),
> +			 GFP_KERNEL);
>  	if (!new_fn)
>  		return -ENOMEM;
>  	new_fn->hash = hash;
> -- 
> 2.46.0
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR