Commit 5e28b7b94408 for kernel

commit 5e28b7b94408897e41c63477aabc9e1db439bc8c
Author: Francis, David <David.Francis@amd.com>
Date:   Tue Apr 28 19:25:50 2026 +0000

    drm: Set old handle to NULL before prime swap in change_handle

    There was a potential race condition in change_handle. The ioctl
    briefly had a single object with two idr entries; a concurrent
    gem_close could delete the object and remove one of the handles
    while leaving the other one dangling, which could subsequently
    be dereferenced for a use-after-free.

    To fix this, do the same dance that gem_close itself does.
    (f6cd7daecff5 drm: Release driver references to handle before making it available again)
    First idr_replace the old handle to NULL. Later, if the prime
    operations are successful, actually close it.

    create_tail required a similar dance to avoid a similar problem.
    (bd46cece51a3 drm/gem: Fix race in drm_gem_handle_create_tail())
    It idr_allocs the new handle with NULL, then swaps in the correct
    object later to avoid races. We don't need to do that here, since
    the only operations that could race are drm_prime, and
    change_handle holds the prime lock for the entire duration.

    v2: cleanups of error paths

    Signed-off-by: David Francis <David.Francis@amd.com>
    Co-authored-by: Dave Airlie <airlied@gmail.com>
    Reported-by: Puttimet Thammasaeng <pwn8official@gmail.com>
    Tested-by: Vitaly Prosyak <Vitaly.Prosyak@amd.com>
    Cc: Simona Vetter <simona@ffwll.ch>
    Cc: stable@vger.kernel.org
    Cc: Christian Koenig <Christian.Koenig@amd.com>
    Fixes: 53096728b8910 ("drm: Add DRM prime interface to reassign GEM handle")
    Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index d6424267260b..51a887cc7fd7 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1019,7 +1019,7 @@ int drm_gem_change_handle_ioctl(struct drm_device *dev, void *data,
 				struct drm_file *file_priv)
 {
 	struct drm_gem_change_handle *args = data;
-	struct drm_gem_object *obj;
+	struct drm_gem_object *obj, *idrobj;
 	int handle, ret;

 	if (!drm_core_check_feature(dev, DRIVER_GEM))
@@ -1042,8 +1042,29 @@ int drm_gem_change_handle_ioctl(struct drm_device *dev, void *data,
 	mutex_lock(&file_priv->prime.lock);

 	spin_lock(&file_priv->table_lock);
+
+       /* When create_tail allocs an obj idr, it needs to first alloc as NULL,
+	* then later replace with the correct object. This is not necessary
+	* here, because the only operations that could race are drm_prime
+	* bookkeeping, and we hold the prime lock.
+	*/
 	ret = idr_alloc(&file_priv->object_idr, obj, handle, handle + 1,
 			GFP_NOWAIT);
+
+       if (ret < 0) {
+	       spin_unlock(&file_priv->table_lock);
+	       goto out_unlock;
+       }
+
+       idrobj = idr_replace(&file_priv->object_idr, NULL, handle);
+       if (idrobj != obj) {
+	       idr_replace(&file_priv->object_idr, idrobj, handle);
+	       idr_remove(&file_priv->object_idr, args->new_handle);
+	       spin_unlock(&file_priv->table_lock);
+	       ret = -ENOENT;
+	       goto out_unlock;
+       }
+
 	spin_unlock(&file_priv->table_lock);

 	if (ret < 0)
@@ -1055,6 +1076,8 @@ int drm_gem_change_handle_ioctl(struct drm_device *dev, void *data,
 		if (ret < 0) {
 			spin_lock(&file_priv->table_lock);
 			idr_remove(&file_priv->object_idr, handle);
+			idrobj = idr_replace(&file_priv->object_idr, obj, handle);
+			WARN_ON(idrobj != NULL);
 			spin_unlock(&file_priv->table_lock);
 			goto out_unlock;
 		}