linux-kernel - [PATCH v2] drm/panthor: Prevent potential UAF in group creation

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Message-Id: <20251127164912.3788155-1-akash.goel@arm.com>
Date: Thu, 27 Nov 2025 16:49:12 +0000
From: Akash Goel <akash.goel@....com>
To: boris.brezillon@...labora.com,
	liviu.dudau@....com,
	steven.price@....com
Cc: dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	maarten.lankhorst@...ux.intel.com,
	mripard@...nel.org,
	tzimmermann@...e.de,
	airlied@...il.com,
	daniel@...ll.ch,
	nd@....com,
	Akash Goel <akash.goel@....com>
Subject: [PATCH v2] drm/panthor: Prevent potential UAF in group creation

This commit prevents the possibility of a use after free issue in the
GROUP_CREATE ioctl function, which arose as pointer to the group is
accessed in that ioctl function after storing it in the Xarray.
A malicious userspace can second guess the handle of a group and try
to call GROUP_DESTROY ioctl from another thread around the same time
as GROUP_CREATE ioctl.

To prevent the use after free exploit, this commit uses a mark on an
entry of group pool Xarray which is added just before returning from
the GROUP_CREATE ioctl function. The mark is checked for all ioctls
that specify the group handle and so userspace won't be abe to delete
a group that isn't marked yet.

v2: Add R-bs and fixes tags

Fixes: de85488138247 ("drm/panthor: Add the scheduler logical block")
Co-developed-by: Boris Brezillon <boris.brezillon@...labora.com>
Signed-off-by: Akash Goel <akash.goel@....com>
Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
Reviewed-by: Steven Price <steven.price@....com>
---
 drivers/gpu/drm/panthor/panthor_sched.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
index b834123a6560..a6b8024e1a3c 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.c
+++ b/drivers/gpu/drm/panthor/panthor_sched.c
@@ -779,6 +779,12 @@ struct panthor_job_profiling_data {
  */
 #define MAX_GROUPS_PER_POOL 128
 
+/*
+ * Mark added on an entry of group pool Xarray to identify if the group has
+ * been fully initialized and can be accessed elsewhere in the driver code.
+ */
+#define GROUP_REGISTERED XA_MARK_1
+
 /**
  * struct panthor_group_pool - Group pool
  *
@@ -3007,7 +3013,7 @@ void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile)
 		return;
 
 	xa_lock(&gpool->xa);
-	xa_for_each(&gpool->xa, i, group) {
+	xa_for_each_marked(&gpool->xa, i, group, GROUP_REGISTERED) {
 		guard(spinlock)(&group->fdinfo.lock);
 		pfile->stats.cycles += group->fdinfo.data.cycles;
 		pfile->stats.time += group->fdinfo.data.time;
@@ -3727,6 +3733,8 @@ int panthor_group_create(struct panthor_file *pfile,
 
 	group_init_task_info(group);
 
+	xa_set_mark(&gpool->xa, gid, GROUP_REGISTERED);
+
 	return gid;
 
 err_erase_gid:
@@ -3744,6 +3752,9 @@ int panthor_group_destroy(struct panthor_file *pfile, u32 group_handle)
 	struct panthor_scheduler *sched = ptdev->scheduler;
 	struct panthor_group *group;
 
+	if (!xa_get_mark(&gpool->xa, group_handle, GROUP_REGISTERED))
+		return -EINVAL;
+
 	group = xa_erase(&gpool->xa, group_handle);
 	if (!group)
 		return -EINVAL;
@@ -3769,12 +3780,12 @@ int panthor_group_destroy(struct panthor_file *pfile, u32 group_handle)
 }
 
 static struct panthor_group *group_from_handle(struct panthor_group_pool *pool,
-					       u32 group_handle)
+					       unsigned long group_handle)
 {
 	struct panthor_group *group;
 
 	xa_lock(&pool->xa);
-	group = group_get(xa_load(&pool->xa, group_handle));
+	group = group_get(xa_find(&pool->xa, &group_handle, group_handle, GROUP_REGISTERED));
 	xa_unlock(&pool->xa);
 
 	return group;
@@ -3861,7 +3872,7 @@ panthor_fdinfo_gather_group_mem_info(struct panthor_file *pfile,
 		return;
 
 	xa_lock(&gpool->xa);
-	xa_for_each(&gpool->xa, i, group) {
+	xa_for_each_marked(&gpool->xa, i, group, GROUP_REGISTERED) {
 		stats->resident += group->fdinfo.kbo_sizes;
 		if (group->csg_id >= 0)
 			stats->active += group->fdinfo.kbo_sizes;
-- 
2.25.1