[ 3.8.y.z extended stable ] Patch "drm: fix a use-after-free when GPU acceleration disabled" has been added to staging queue

[Kamal Mostafa]

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

    drm: fix a use-after-free when GPU acceleration disabled

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.3.

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

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From efe4df2ae6302d6fdbb7b460d8747fe50e2aa4d0 Mon Sep 17 00:00:00 2001
From: Huacai Chen <chenhc at lemote.com>
Date: Tue, 21 May 2013 06:23:43 +0000
Subject: drm: fix a use-after-free when GPU acceleration disabled
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit b7ea85a4fed37835eec78a7be3039c8dc22b8178 upstream.

When GPU acceleration is disabled, drm_vblank_cleanup() will free the
vblank-related data, such as vblank_refcount, vblank_inmodeset, etc.
But we found that drm_vblank_post_modeset() may be called after the
cleanup, which use vblank_refcount and vblank_inmodeset. And this will
cause a kernel panic.

Fix this by return immediately if dev->num_crtcs is zero. This is the
same thing that drm_vblank_pre_modeset() does.

Call trace of a drm_vblank_post_modeset() after drm_vblank_cleanup():
[   62.628906] [<ffffffff804868d0>] drm_vblank_post_modeset+0x34/0xb4
[   62.628906] [<ffffffff804c7008>] atombios_crtc_dpms+0xb4/0x174
[   62.628906] [<ffffffff804c70e0>] atombios_crtc_commit+0x18/0x38
[   62.628906] [<ffffffff8047f038>] drm_crtc_helper_set_mode+0x304/0x3cc
[   62.628906] [<ffffffff8047f92c>] drm_crtc_helper_set_config+0x6d8/0x988
[   62.628906] [<ffffffff8047dd40>] drm_fb_helper_set_par+0x94/0x104
[   62.628906] [<ffffffff80439d14>] fbcon_init+0x424/0x57c
[   62.628906] [<ffffffff8046a638>] visual_init+0xb8/0x118
[   62.628906] [<ffffffff8046b9f8>] take_over_console+0x238/0x384
[   62.628906] [<ffffffff80436df8>] fbcon_takeover+0x7c/0xdc
[   62.628906] [<ffffffff8024fa20>] notifier_call_chain+0x44/0x94
[   62.628906] [<ffffffff8024fcbc>] __blocking_notifier_call_chain+0x48/0x68
[   62.628906] [<ffffffff8042d990>] register_framebuffer+0x228/0x260
[   62.628906] [<ffffffff8047e010>] drm_fb_helper_single_fb_probe+0x260/0x314
[   62.628906] [<ffffffff8047e2c4>] drm_fb_helper_initial_config+0x200/0x234
[   62.628906] [<ffffffff804e5560>] radeon_fbdev_init+0xd4/0xf4
[   62.628906] [<ffffffff804e0e08>] radeon_modeset_init+0x9bc/0xa18
[   62.628906] [<ffffffff804bfc14>] radeon_driver_load_kms+0xdc/0x12c
[   62.628906] [<ffffffff8048b548>] drm_get_pci_dev+0x148/0x238
[   62.628906] [<ffffffff80423564>] local_pci_probe+0x5c/0xd0
[   62.628906] [<ffffffff80241ac4>] work_for_cpu_fn+0x1c/0x30
[   62.628906] [<ffffffff802427c8>] process_one_work+0x274/0x3bc
[   62.628906] [<ffffffff80242934>] process_scheduled_works+0x24/0x44
[   62.628906] [<ffffffff8024515c>] worker_thread+0x31c/0x3f4
[   62.628906] [<ffffffff802497a8>] kthread+0x88/0x90
[   62.628906] [<ffffffff80206794>] kernel_thread_helper+0x10/0x18

Signed-off-by: Huacai Chen <chenhc at lemote.com>
Signed-off-by: Binbin Zhou <zhoubb at lemote.com>
Reviewed-by: Michel Dänzer <michel.daenzer at amd.com>
Acked-by: Paul Menzel <paulepanter at users.sourceforge.net>
Signed-off-by: Dave Airlie <airlied at gmail.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/drm_irq.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 19c01ca..570dac6 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1049,7 +1049,7 @@ EXPORT_SYMBOL(drm_vblank_off);
  */
 void drm_vblank_pre_modeset(struct drm_device *dev, int crtc)
 {
-	/* vblank is not initialized (IRQ not installed ?) */
+	/* vblank is not initialized (IRQ not installed ?), or has been freed */
 	if (!dev->num_crtcs)
 		return;
 	/*
@@ -1071,6 +1071,10 @@ void drm_vblank_post_modeset(struct drm_device *dev, int crtc)
 {
 	unsigned long irqflags;

+	/* vblank is not initialized (IRQ not installed ?), or has been freed */
+	if (!dev->num_crtcs)
+		return;
+
 	if (dev->vblank_inmodeset[crtc]) {
 		spin_lock_irqsave(&dev->vbl_lock, irqflags);
 		dev->vblank_disable_allowed = 1;
--
1.8.1.2