tty/vt: don't set font mappings on vc not supporting this

commit 9e326f78 upstream.

We can call this function for a dummy console that doesn't support
setting the font mapping, which will result in a null ptr BUG. So check
for this case and return error for consoles w/o font mapping support.

Reference: https://bugzilla.kernel.org/show_bug.cgi?id=59321Signed-off-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[lizf: Backported to 3.4: just return -EINVAL as we don't need to unlock]
Signed-off-by: Zefan Li <lizefan@huawei.com>

drivers/tty/vt/consolemap.c

@@ -518,6 +518,10 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list)
 
 	/* Save original vc_unipagdir_loc in case we allocate a new one */
 	p = (struct uni_pagedir *)*vc->vc_uni_pagedir_loc;
+
+	if (!p)
+		return -EINVAL;
+
 	if (p->readonly) return -EIO;
 	
 	if (!ct) return 0;