[3.16.y-ckt stable] Patch "video/logo: prevent use of logos after they have been freed" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    video/logo: prevent use of logos after they have been freed

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 90dbca4f3621280eb7b1051413f5731284a35098 Mon Sep 17 00:00:00 2001
From: Tomi Valkeinen <tomi.valkeinen at ti.com>
Date: Thu, 18 Dec 2014 13:40:06 +0200
Subject: video/logo: prevent use of logos after they have been freed

commit 92b004d1aa9f367c372511ca0330f58216b25703 upstream.

If the probe of an fb driver has been deferred due to missing
dependencies, and the probe is later ran when a module is loaded, the
fbdev framework will try to find a logo to use.

However, the logos are __initdata, and have already been freed. This
causes sometimes page faults, if the logo memory is not mapped,
sometimes other random crashes as the logo data is invalid, and
sometimes nothing, if the fbdev decides to reject the logo (e.g. the
random value depicting the logo's height is too big).

This patch adds a late_initcall function to mark the logos as freed. In
reality the logos are freed later, and fbdev probe may be ran between
this late_initcall and the freeing of the logos. In that case we will
miss drawing the logo, even if it would be possible.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/video/logo/logo.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/video/logo/logo.c b/drivers/video/logo/logo.c
index 940cd196eef5..10fbfd8ab963 100644
--- a/drivers/video/logo/logo.c
+++ b/drivers/video/logo/logo.c
@@ -21,6 +21,21 @@ static bool nologo;
 module_param(nologo, bool, 0);
 MODULE_PARM_DESC(nologo, "Disables startup logo");

+/*
+ * Logos are located in the initdata, and will be freed in kernel_init.
+ * Use late_init to mark the logos as freed to prevent any further use.
+ */
+
+static bool logos_freed;
+
+static int __init fb_logo_late_init(void)
+{
+	logos_freed = true;
+	return 0;
+}
+
+late_initcall(fb_logo_late_init);
+
 /* logo's are marked __initdata. Use __init_refok to tell
  * modpost that it is intended that this function uses data
  * marked __initdata.
@@ -29,7 +44,7 @@ const struct linux_logo * __init_refok fb_find_logo(int depth)
 {
 	const struct linux_logo *logo = NULL;

-	if (nologo)
+	if (nologo || logos_freed)
 		return NULL;

 	if (depth >= 1) {
--
2.1.4