Re: [PATCH 12/19] pramfs: symlink operations

[Al Viro <viro@ZenIV.linux.org.uk>]

On Sat, Sep 07, 2013 at 10:29:15AM +0200, Marco Stornelli wrote:
> +static int pram_readlink(struct dentry *dentry, char __user *buffer, int buflen)
> +{
> +	struct inode *inode = dentry->d_inode;
> +	struct super_block *sb = inode->i_sb;
> +	u64 block;
> +	char *blockp;
> +
> +	block = pram_find_data_block(inode, 0);
> +	blockp = pram_get_block(sb, block);
> +	return vfs_readlink(dentry, buffer, buflen, blockp);
> +}

> +static void *pram_follow_link(struct dentry *dentry, struct nameidata *nd)
> +{
> +	struct inode *inode = dentry->d_inode;
> +	struct super_block *sb = inode->i_sb;
> +	off_t block;
> +	int status;
> +	char *blockp;
> +
> +	block = pram_find_data_block(inode, 0);
> +	blockp = pram_get_block(sb, block);
> +	status = vfs_follow_link(nd, blockp);
> +	return ERR_PTR(status);
> +}

Just nd_set_link(nd, blockp) instead of that vfs_follow_link() and be
done with that; that way you can use generic_readlink() instead of
pram_readlink() *and* get lower stack footprint on traversing them.

BTW, where's the error checking?  pram_get_block()/pram_find_data_block()
seem to assume that fs image isn't corrupted and if it is... that code
will happily dereference any address.  At least range checks of some sort
in pram_get_block() (and checking if it has failed) would be a good idea...