Re: [PATCH] vfs: check ->get_link return value

[Matthew Wilcox <willy@infradead.org>]

On Mon, Oct 01, 2018 at 03:45:00PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Teach callers of inode->i_op->get_link in the vfs code to check for a
> NULL return value and return an error status instead of blindly
> dereferencing the returned NULL pointer.

Is that better than having the get_link method return ERR_PTR(-EUCLEAN) itself?

> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/namei.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 0cab6494978c..0744ab981fa0 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4737,6 +4737,8 @@ int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen)
>  		if (IS_ERR(link))
>  			return PTR_ERR(link);
>  	}
> +	if (!link)
> +		return -EUCLEAN;
>  	res = readlink_copy(buffer, buflen, link);
>  	do_delayed_call(&done);
>  	return res;
> @@ -4763,6 +4765,8 @@ const char *vfs_get_link(struct dentry *dentry, struct delayed_call *done)
>  		res = ERR_PTR(security_inode_readlink(dentry));
>  		if (!res)
>  			res = inode->i_op->get_link(dentry, inode, done);
> +		if (!res)
> +			return ERR_PTR(-EUCLEAN);
>  	}
>  	return res;
>  }