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[3.19.y-ckt,49/66] drm/dp/mst: Validate port in drm_dp_payload_send_msg()

Message ID 1461702297-7792-50-git-send-email-kamal@canonical.com
State New
Headers show

Commit Message

Kamal Mostafa April 26, 2016, 8:24 p.m. UTC 
3.19.8-ckt20 -stable review patch.  If anyone has any objections, please let me know.

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

From: "cpaul@redhat.com" <cpaul@redhat.com>

commit deba0a2af9592b2022a0bce7b085a318b53ce1db upstream.

With the joys of things running concurrently, there's always a chance
that the port we get passed in drm_dp_payload_send_msg() isn't actually
valid anymore. Because of this, we need to make sure we validate the
reference to the port before we use it otherwise we risk running into
various race conditions. For instance, on the Dell MST monitor I have
here for testing, hotplugging it enough times causes us to kernel panic:

[drm:intel_mst_enable_dp] 1
[drm:drm_dp_update_payload_part2] payload 0 1
[drm:intel_get_hpd_pins] hotplug event received, stat 0x00200000, dig 0x10101011, pins 0x00000020
[drm:intel_hpd_irq_handler] digital hpd port B - short
[drm:intel_dp_hpd_pulse] got hpd irq on port B - short
[drm:intel_dp_check_mst_status] got esi 00 10 00
[drm:drm_dp_update_payload_part2] payload 1 1
general protection fault: 0000 [#1] SMP
…
Call Trace:
 [<ffffffffa012b632>] drm_dp_update_payload_part2+0xc2/0x130 [drm_kms_helper]
 [<ffffffffa032ef08>] intel_mst_enable_dp+0xf8/0x180 [i915]
 [<ffffffffa0310dbd>] haswell_crtc_enable+0x3ed/0x8c0 [i915]
 [<ffffffffa030c84d>] intel_atomic_commit+0x5ad/0x1590 [i915]
 [<ffffffffa01db877>] ? drm_atomic_set_crtc_for_connector+0x57/0xe0 [drm]
 [<ffffffffa01dc4e7>] drm_atomic_commit+0x37/0x60 [drm]
 [<ffffffffa0130a3a>] drm_atomic_helper_set_config+0x7a/0xb0 [drm_kms_helper]
 [<ffffffffa01cc482>] drm_mode_set_config_internal+0x62/0x100 [drm]
 [<ffffffffa01d02ad>] drm_mode_setcrtc+0x3cd/0x4e0 [drm]
 [<ffffffffa01c18e3>] drm_ioctl+0x143/0x510 [drm]
 [<ffffffffa01cfee0>] ? drm_mode_setplane+0x1b0/0x1b0 [drm]
 [<ffffffff810f79a7>] ? hrtimer_start_range_ns+0x1b7/0x3a0
 [<ffffffff81212962>] do_vfs_ioctl+0x92/0x570
 [<ffffffff81590852>] ? __sys_recvmsg+0x42/0x80
 [<ffffffff81212eb9>] SyS_ioctl+0x79/0x90
 [<ffffffff816b4e32>] entry_SYSCALL_64_fastpath+0x1a/0xa4
RIP  [<ffffffffa012b026>] drm_dp_payload_send_msg+0x146/0x1f0 [drm_kms_helper]

Which occurs because of the hotplug event shown in the log, which ends
up causing DRM's dp helpers to drop the port we're updating the payload
on and panic.

Signed-off-by: Lyude <cpaul@redhat.com>
Reviewed-by: David Airlie <airlied@linux.ie>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
diff mbox

Patch

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index aafd687..aab5614 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1653,13 +1653,19 @@  static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 	struct drm_dp_mst_branch *mstb;
 	int len, ret, port_num;
 
+	port = drm_dp_get_validated_port_ref(mgr, port);
+	if (!port)
+		return -EINVAL;
+
 	port_num = port->port_num;
 	mstb = drm_dp_get_validated_mstb_ref(mgr, port->parent);
 	if (!mstb) {
 		mstb = drm_dp_get_last_connected_port_and_mstb(mgr, port->parent, &port_num);
 
-		if (!mstb)
+		if (!mstb) {
+			drm_dp_put_port(port);
 			return -EINVAL;
+		}
 	}
 
 	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
@@ -1685,6 +1691,7 @@  static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 	kfree(txmsg);
 fail_put:
 	drm_dp_put_mst_branch_device(mstb);
+	drm_dp_put_port(port);
 	return ret;
 }