Code: static __always_inline int __do_follow_link(struct path *path, struct nameidata *nd)
{
	int error;
	void *cookie;
	struct dentry *dentry = path->dentry;

	touch_atime(path->mnt, dentry);
	nd_set_link(nd, NULL);

	if (path->mnt != nd->path.mnt) {
		path_to_nameidata(path, nd);
 		dget(dentry);
 	}
 	mntget(path->mnt);
 	cookie = dentry->d_inode->i_op->follow_link(dentry, nd);
 	error = PTR_ERR(cookie);
 	if (!IS_ERR(cookie)) {
		char *s = nd_get_link(nd);
		error = 0;
		if (s)
			error = __vfs_follow_link(nd, s);
		else if (nd->last_type == LAST_BIND) {
			error = force_reval_path(&nd->path, nd);
			if (error)
				path_put(&nd->path);
		}
		if (dentry->d_inode->i_op->put_link)
			dentry->d_inode->i_op->put_link(dentry, nd, cookie);
	}
	return error;
}

Vulnerability Type: DoS 
CWE ID: CWE-20
Summary: The __do_follow_link function in fs/namei.c in the Linux kernel before 2.6.33 does not properly handle the last pathname component during use of certain filesystems, which allows local users to cause a denial of service (incorrect free operations and system crash) via an open system call.
Commit Message: fix autofs/afs/etc. magic mountpoint breakage

We end up trying to kfree() nd.last.name on open("/mnt/tmp", O_CREAT)
if /mnt/tmp is an autofs direct mount.  The reason is that nd.last_type
is bogus here; we want LAST_BIND for everything of that kind and we
get LAST_NORM left over from finding parent directory.

So make sure that it *is* set properly; set to LAST_BIND before
doing ->follow_link() - for normal symlinks it will be changed
by __vfs_follow_link() and everything else needs it set that way.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>