[4.2.y-ckt stable] Patch "drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1()" has been added to the 4.2.y-ckt tree

Kamal Mostafa kamal at canonical.com
Mon May 9 19:43:33 UTC 2016


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

    drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1()

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt10.

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

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 134f51cd24a425cbb071f1ba8ccd0c7c28952bfb Mon Sep 17 00:00:00 2001
From: "cpaul at redhat.com" <cpaul at redhat.com>
Date: Fri, 22 Apr 2016 16:08:46 -0400
Subject: drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1()

commit 263efde31f97c498e1ebad30e4d2906609d7ad6b upstream.

We can thank KASAN for finding this, otherwise I probably would have spent
hours on it. This fixes a somewhat harder to trigger kernel panic, occuring
while enabling MST where the port we were currently updating the payload on
would have all of it's refs dropped before we finished what we were doing:

==================================================================
BUG: KASAN: use-after-free in drm_dp_update_payload_part1+0xb3f/0xdb0 [drm_kms_helper] at addr ffff8800d29de018
Read of size 4 by task Xorg/973
=============================================================================
BUG kmalloc-2048 (Tainted: G    B   W      ): kasan: bad access detected
-----------------------------------------------------------------------------

INFO: Allocated in drm_dp_add_port+0x1aa/0x1ed0 [drm_kms_helper] age=16477 cpu=0 pid=2175
	___slab_alloc+0x472/0x490
	__slab_alloc+0x20/0x40
	kmem_cache_alloc_trace+0x151/0x190
	drm_dp_add_port+0x1aa/0x1ed0 [drm_kms_helper]
	drm_dp_send_link_address+0x526/0x960 [drm_kms_helper]
	drm_dp_check_and_send_link_address+0x1ac/0x210 [drm_kms_helper]
	drm_dp_mst_link_probe_work+0x77/0xd0 [drm_kms_helper]
	process_one_work+0x562/0x1350
	worker_thread+0xd9/0x1390
	kthread+0x1c5/0x260
	ret_from_fork+0x22/0x40
INFO: Freed in drm_dp_free_mst_port+0x50/0x60 [drm_kms_helper] age=7521 cpu=0 pid=2175
	__slab_free+0x17f/0x2d0
	kfree+0x169/0x180
	drm_dp_free_mst_port+0x50/0x60 [drm_kms_helper]
	drm_dp_destroy_connector_work+0x2b8/0x490 [drm_kms_helper]
	process_one_work+0x562/0x1350
	worker_thread+0xd9/0x1390
	kthread+0x1c5/0x260
	ret_from_fork+0x22/0x40

which on this T460s, would eventually lead to kernel panics in somewhat
random places later in intel_mst_enable_dp() if we got lucky enough.

Signed-off-by: Lyude <cpaul at redhat.com>
Signed-off-by: Dave Airlie <airlied at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index e001149..246aafa 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1779,6 +1779,11 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
 		req_payload.start_slot = cur_slots;
 		if (mgr->proposed_vcpis[i]) {
 			port = container_of(mgr->proposed_vcpis[i], struct drm_dp_mst_port, vcpi);
+			port = drm_dp_get_validated_port_ref(mgr, port);
+			if (!port) {
+				mutex_unlock(&mgr->payload_lock);
+				return -EINVAL;
+			}
 			req_payload.num_slots = mgr->proposed_vcpis[i]->num_slots;
 		} else {
 			port = NULL;
@@ -1804,6 +1809,9 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
 			mgr->payloads[i].payload_state = req_payload.payload_state;
 		}
 		cur_slots += req_payload.num_slots;
+
+		if (port)
+			drm_dp_put_port(port);
 	}

 	for (i = 0; i < mgr->max_payloads; i++) {
--
2.7.4





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