linux-kernel - Re: [PATCH, v2] sysv: ensure link targets are NUL-terminated

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Date:	Mon, 15 Dec 2008 10:12:33 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Duane Griffin <duaneg@...da.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Boaz Harrosh <bharrosh@...asas.com>, hch@...radead.org
Subject: Re: [PATCH, v2] sysv: ensure link targets are NUL-terminated

On Thu, Dec 11, 2008 at 10:35:32PM +0000, Duane Griffin wrote:
> Ensure link targets are NUL-terminated, even if corrupted on-disk.
> 
> Signed-off-by: Duane Griffin <duaneg@...da.com>
> ---
> 
> V2: terminate when the link is read instead of every time it is
> followed, as suggested by Dave Kleikamp.
> 
> diff --git a/fs/sysv/inode.c b/fs/sysv/inode.c
> index df0d435..1511228 100644
> --- a/fs/sysv/inode.c
> +++ b/fs/sysv/inode.c
> @@ -163,8 +163,10 @@ void sysv_set_inode(struct inode *inode, dev_t rdev)
>  		if (inode->i_blocks) {
>  			inode->i_op = &sysv_symlink_inode_operations;
>  			inode->i_mapping->a_ops = &sysv_aops;
> -		} else
> +		} else {
>  			inode->i_op = &sysv_fast_symlink_inode_operations;
> +			((char *) SYSV_I(inode)->i_data)[inode->i_size] = '\0';

If you do it that way, you want to verify that i_size is bounded.  Better yet,
add a helper for that (taking void *, len, max_len)
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