Re: [PATCH, v5] eCryptfs: check readlink result was not an error before using it

[Dustin Kirkland <kirkland@canonical.com>]

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On Fri, 2008-12-19 at 20:47 +0000, Duane Griffin wrote:
> The result from readlink is being used to index into the link name
> buffer without checking whether it is a valid length. If readlink
> returns an error this will fault or cause memory corruption.
> 
> Cc: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
> Cc: Dustin Kirkland <kirkland@canonical.com>

Acked-by: Dustin Kirkland <kirkland@canonical.com>

> Cc: ecryptfs-devel@lists.launchpad.net
> Signed-off-by: Duane Griffin <duaneg@dghda.com>
> Acked-by: Michael Halcrow <mhalcrow@us.ibm.com>
> ---
> 
> Unchanged from original version.
> 
>  fs/ecryptfs/inode.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
> index 89209f0..5e78fc1 100644
> --- a/fs/ecryptfs/inode.c
> +++ b/fs/ecryptfs/inode.c
> @@ -673,10 +673,11 @@ static void *ecryptfs_follow_link(struct dentry *dentry, struct nameidata *nd)
>  	ecryptfs_printk(KERN_DEBUG, "Calling readlink w/ "
>  			"dentry->d_name.name = [%s]\n", dentry->d_name.name);
>  	rc = dentry->d_inode->i_op->readlink(dentry, (char __user *)buf, len);
> -	buf[rc] = '\0';
>  	set_fs(old_fs);
>  	if (rc < 0)
>  		goto out_free;
> +	else
> +		buf[rc] = '\0';
>  	rc = 0;
>  	nd_set_link(nd, buf);
>  	goto out;

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