FAILED: patch "[PATCH] drm/dp_mst: Fix NULL deref in" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x 3d887d512494d678b17c57b835c32f4e48d34f26
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023102723-steerable-trench-2f00@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3d887d512494d678b17c57b835c32f4e48d34f26 Mon Sep 17 00:00:00 2001
From: Lukasz Majczak <[email protected]>
Date: Fri, 22 Sep 2023 08:34:10 +0200
Subject: [PATCH] drm/dp_mst: Fix NULL deref in
get_mst_branch_device_by_guid_helper()

As drm_dp_get_mst_branch_device_by_guid() is called from drm_dp_get_mst_branch_device_by_guid(), mstb parameter has to be checked, otherwise NULL dereference may occur in the call to
the memcpy() and cause following:

[12579.365869] BUG: kernel NULL pointer dereference, address: 0000000000000049
[12579.365878] #PF: supervisor read access in kernel mode
[12579.365880] #PF: error_code(0x0000) - not-present page
[12579.365882] PGD 0 P4D 0
[12579.365887] Oops: 0000 [#1] PREEMPT SMP NOPTI
...
[12579.365895] Workqueue: events_long drm_dp_mst_up_req_work
[12579.365899] RIP: 0010:memcmp+0xb/0x29
[12579.365921] Call Trace:
[12579.365927] get_mst_branch_device_by_guid_helper+0x22/0x64
[12579.365930] drm_dp_mst_up_req_work+0x137/0x416
[12579.365933] process_one_work+0x1d0/0x419
[12579.365935] worker_thread+0x11a/0x289
[12579.365938] kthread+0x13e/0x14f
[12579.365941] ? process_one_work+0x419/0x419
[12579.365943] ? kthread_blkcg+0x31/0x31
[12579.365946] ret_from_fork+0x1f/0x30

As get_mst_branch_device_by_guid_helper() is recursive, moving condition to the first line allow to remove a similar one for step over of NULL elements inside a loop.

index ed96cfcfa304..8c929ef72c72 100644
@@ -2574,14 +2574,14 @@ static struct drm_dp_mst_branch *get_mst_branch_device_by_guid_helper(
 	struct drm_dp_mst_branch *found_mstb;
 	struct drm_dp_mst_port *port;
 
+	if (!mstb)
+		return NULL;
+
 	if (memcmp(mstb->guid, guid, 16) == 0)
 		return mstb;
 
 
 	list_for_each_entry(port, &mstb->ports, next) {
-		if (!port->mstb)
-			continue;
-
 		found_mstb = get_mst_branch_device_by_guid_helper(port->mstb, guid);
 
 		if (found_mstb)

As drm_dp_get_mst_branch_device_by_guid() is called from drm_dp_get_mst_branch_device_by_guid(), mstb parameter has to be checked, otherwise NULL dereference may occur in the call to
the memcpy() and cause following:

[12579.365869] BUG: kernel NULL pointer dereference, address: 0000000000000049
[12579.365878] #PF: supervisor read access in kernel mode
[12579.365880] #PF: error_code(0x0000) - not-present page
[12579.365882] PGD 0 P4D 0
[12579.365887] Oops: 0000 [#1] PREEMPT SMP NOPTI
...
[12579.365895] Workqueue: events_long drm_dp_mst_up_req_work
[12579.365899] RIP: 0010:memcmp+0xb/0x29
[12579.365921] Call Trace:
[12579.365927] get_mst_branch_device_by_guid_helper+0x22/0x64
[12579.365930] drm_dp_mst_up_req_work+0x137/0x416
[12579.365933] process_one_work+0x1d0/0x419
[12579.365935] worker_thread+0x11a/0x289
[12579.365938] kthread+0x13e/0x14f
[12579.365941] ? process_one_work+0x419/0x419
[12579.365943] ? kthread_blkcg+0x31/0x31
[12579.365946] ret_from_fork+0x1f/0x30

As get_mst_branch_device_by_guid_helper() is recursive, moving condition to the first line allow to remove a similar one for step over of NULL elements inside a loop.

---
 drivers/gpu/drm/drm_dp_mst_topology.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

index 1ff13af13324..7b396b7277ee 100644
@@ -1806,14 +1806,14 @@ static struct drm_dp_mst_branch *get_mst_branch_device_by_guid_helper(
 	struct drm_dp_mst_branch *found_mstb;
 	struct drm_dp_mst_port *port;
 
+	if (!mstb)
+		return NULL;
+
 	if (memcmp(mstb->guid, guid, 16) == 0)
 		return mstb;
 
 
 	list_for_each_entry(port, &mstb->ports, next) {
-		if (!port->mstb)
-			continue;
-
 		found_mstb = get_mst_branch_device_by_guid_helper(port->mstb, guid);
 
 		if (found_mstb)

2.42.0.820.g83a721a137-goog

All now queued up, thanks.

greg k-h