[syzbot] [dri?] KASAN: slab-use-after-free Read in drm_gem_object_release_handle

[syzbot] [dri?] KASAN: slab-use-after-free Read in drm_gem_object_release_handle

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f5459048c38a Merge tag 'i2c-for-7.0-final' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1028d106580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6754c86e8d9e4c91
dashboard link: https://syzkaller.appspot.com/bug?extid=b2e951687503f32f74ce
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1428d106580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17509036580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/530844b89fdc/disk-f5459048.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/551ba51d047c/vmlinux-f5459048.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9e6a44490566/bzImage-f5459048.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b2e951687503f32f74ce@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in drm_gem_object_release_handle+0x4b/0x1e0 drivers/gpu/drm/drm_gem.c:374
Read of size 8 at addr ffff88806c6ffa88 by task syz.1.18/6089

CPU: 1 UID: 0 PID: 6089 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 drm_gem_object_release_handle+0x4b/0x1e0 drivers/gpu/drm/drm_gem.c:374
 idr_for_each+0x1c6/0x2a0 lib/idr.c:210
 drm_gem_release+0x28/0x40 drivers/gpu/drm/drm_gem.c:1088
 drm_file_free+0x729/0xa00 drivers/gpu/drm/drm_file.c:261
 drm_close_helper drivers/gpu/drm/drm_file.c:290 [inline]
 drm_release+0x2de/0x3f0 drivers/gpu/drm/drm_file.c:438
 __fput+0x44f/0xa70 fs/file_table.c:469
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
 exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efc3279c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc28821858 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007ffc28821940 RCX: 00007efc3279c819
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 000000000001956f R08: 0000000000000001 R09: 0000000000000000
R10: 0000001b2f520000 R11: 0000000000000246 R12: 00007ffc28821980
R13: 00007efc32a1609c R14: 00000000000195b1 R15: 00007efc32a16090
 </TASK>

Allocated by task 6090:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 __drm_gem_shmem_create+0xc4/0x2e0 drivers/gpu/drm/drm_gem_shmem_helper.c:130
 drm_gem_shmem_create drivers/gpu/drm/drm_gem_shmem_helper.c:157 [inline]
 drm_gem_shmem_create_with_handle drivers/gpu/drm/drm_gem_shmem_helper.c:460 [inline]
 drm_gem_shmem_dumb_create+0x72/0x120 drivers/gpu/drm/drm_gem_shmem_helper.c:549
 drm_mode_create_dumb drivers/gpu/drm/drm_dumb_buffers.c:227 [inline]
 drm_mode_create_dumb_ioctl+0x2bd/0x340 drivers/gpu/drm/drm_dumb_buffers.c:236
 drm_ioctl_kernel+0x2df/0x3b0 drivers/gpu/drm/drm_ioctl.c:804
 drm_ioctl+0x6ba/0xb80 drivers/gpu/drm/drm_ioctl.c:901
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6093:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 drm_gem_object_release_handle+0xc2/0x1e0 drivers/gpu/drm/drm_gem.c:385
 drm_gem_handle_delete+0x7b/0xb0 drivers/gpu/drm/drm_gem.c:413
 drm_ioctl_kernel+0x2df/0x3b0 drivers/gpu/drm/drm_ioctl.c:804
 drm_ioctl+0x6ba/0xb80 drivers/gpu/drm/drm_ioctl.c:901
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88806c6ff800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 648 bytes inside of
 freed 1024-byte region [ffff88806c6ff800, ffff88806c6ffc00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x6c6f8
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813fea6dc0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813fea6dc0 dead000000000100 dead000000000122
head: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0001b1be01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5954, tgid 5954 (syz-executor), ts 103695420380, free_ts 92416780237
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_node_noprof+0x577/0x7c0 mm/slub.c:5266
 kmalloc_node_noprof include/linux/slab.h:1081 [inline]
 qdisc_alloc+0x92/0x9e0 net/sched/sch_generic.c:951
 qdisc_create_dflt+0x8e/0x510 net/sched/sch_generic.c:1006
 attach_one_default_qdisc net/sched/sch_generic.c:1172 [inline]
 netdev_for_each_tx_queue include/linux/netdevice.h:2684 [inline]
 attach_default_qdiscs net/sched/sch_generic.c:1190 [inline]
 dev_activate+0x378/0x1150 net/sched/sch_generic.c:1249
 __dev_open+0x67a/0x830 net/core/dev.c:1711
 __dev_change_flags+0x1f7/0x690 net/core/dev.c:9781
 netif_change_flags+0x88/0x1a0 net/core/dev.c:9844
 do_setlink+0xf82/0x4590 net/core/rtnetlink.c:3180
 rtnl_changelink net/core/rtnetlink.c:3798 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3971 [inline]
 rtnl_newlink+0x15ad/0x1bb0 net/core/rtnetlink.c:4108
 rtnetlink_rcv_msg+0x7d5/0xbe0 net/core/rtnetlink.c:6994
page last free pid 5854 tgid 5854 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 vfree+0x25a/0x400 mm/vmalloc.c:3479
 kcov_put kernel/kcov.c:442 [inline]
 kcov_close+0x28/0x50 kernel/kcov.c:543
 __fput+0x44f/0xa70 fs/file_table.c:469
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x70f/0x23c0 kernel/exit.c:976
 do_group_exit+0x21b/0x2d0 kernel/exit.c:1118
 get_signal+0x1284/0x1330 kernel/signal.c:3034
 arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0x86/0x480 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88806c6ff980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88806c6ffa00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88806c6ffa80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88806c6ffb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88806c6ffb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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[PATCH] drm: Avoid the chaotic interleaving of change and delete handle

[Edward Adam Davis]

First, let's take a look at how GEM object is freed:
CPU0					CPU1
====					====
drm_gem_change_handle_ioctl()
 drm_gem_object_lookup() // got GEM obj and refcnt is 2
 ... blocks on prime.lock
					drm_gem_handle_delete()
	                                 drm_gem_object_release_handle()
					  ... acquires prime.lock
					  drm_prime_remove_buf_handle()
					  ... unlock prime.lock
					  drm_gem_object_handle_put_unlocked()
					   drm_gem_object_put() // obj refcnt is 1
 ... acquires prime.lock
 drm_gem_object_put() // obj refcnt is 0
  drm_gem_shmem_free() // obj is freed

After a GEM object has been freed, a Use-After-Free vulnerability [1]
is triggered when closes the DRM file, as the drm_gem_release() function
attempts to access the already-freed GEM object.

Adjust the change handle ioctl and handle delete ioctl to be atomic
operations; this prevents simultaneous change and delete operations
on the same GEM object from interfering with the release of the GEM
object during the closing of the DRM file.

[1]
BUG: KASAN: slab-use-after-free in drm_gem_object_release_handle+0x4b/0x1e0 drivers/gpu/drm/drm_gem.c:374
Call Trace:
 drm_gem_object_release_handle+0x4b/0x1e0 drivers/gpu/drm/drm_gem.c:374
 idr_for_each+0x1c6/0x2a0 lib/idr.c:210
 drm_gem_release+0x28/0x40 drivers/gpu/drm/drm_gem.c:1088
 drm_file_free+0x729/0xa00 drivers/gpu/drm/drm_file.c:261
 drm_close_helper drivers/gpu/drm/drm_file.c:290 [inline]
 drm_release+0x2de/0x3f0 drivers/gpu/drm/drm_file.c:438

Allocated by task 6090:
 __drm_gem_shmem_create+0xc4/0x2e0 drivers/gpu/drm/drm_gem_shmem_helper.c:130
 drm_gem_shmem_create drivers/gpu/drm/drm_gem_shmem_helper.c:157 [inline]
 drm_gem_shmem_create_with_handle drivers/gpu/drm/drm_gem_shmem_helper.c:460 [inline]
 drm_gem_shmem_dumb_create+0x72/0x120 drivers/gpu/drm/drm_gem_shmem_helper.c:549
 
Freed by task 6093:
 drm_gem_object_release_handle+0xc2/0x1e0 drivers/gpu/drm/drm_gem.c:385
 drm_gem_handle_delete+0x7b/0xb0 drivers/gpu/drm/drm_gem.c:413
 drm_ioctl_kernel+0x2df/0x3b0 drivers/gpu/drm/drm_ioctl.c:804

Fixes: 53096728b891 ("drm: Add DRM prime interface to reassign GEM handle")
Reported-by: syzbot+b2e951687503f32f74ce@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b2e951687503f32f74ce
Tested-by: syzbot+b2e951687503f32f74ce@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 drivers/gpu/drm/drm_gem.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 891c3bff5ae0..63a8d7e980b5 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -374,14 +374,8 @@ drm_gem_object_release_handle(int id, void *ptr, void *data)
 	if (obj->funcs->close)
 		obj->funcs->close(obj, file_priv);
 
-	mutex_lock(&file_priv->prime.lock);
-
 	drm_prime_remove_buf_handle(&file_priv->prime, id);
-
-	mutex_unlock(&file_priv->prime.lock);
-
 	drm_vma_node_revoke(&obj->vma_node, file_priv);
-
 	drm_gem_object_handle_put_unlocked(obj);
 
 	return 0;
@@ -401,13 +395,16 @@ drm_gem_handle_delete(struct drm_file *filp, u32 handle)
 {
 	struct drm_gem_object *obj;
 
+	mutex_lock(&filp->prime.lock);
 	spin_lock(&filp->table_lock);
 
 	/* Check if we currently have a reference on the object */
 	obj = idr_replace(&filp->object_idr, NULL, handle);
 	spin_unlock(&filp->table_lock);
-	if (IS_ERR_OR_NULL(obj))
+	if (IS_ERR_OR_NULL(obj)) {
+		mutex_unlock(&filp->prime.lock);
 		return -EINVAL;
+	}
 
 	/* Release driver's reference and decrement refcount. */
 	drm_gem_object_release_handle(handle, obj, filp);
@@ -416,6 +413,7 @@ drm_gem_handle_delete(struct drm_file *filp, u32 handle)
 	spin_lock(&filp->table_lock);
 	idr_remove(&filp->object_idr, handle);
 	spin_unlock(&filp->table_lock);
+	mutex_unlock(&filp->prime.lock);
 
 	return 0;
 }
@@ -1012,17 +1010,18 @@ int drm_gem_change_handle_ioctl(struct drm_device *dev, void *data,
 		return -EINVAL;
 	handle = args->new_handle;
 
+	mutex_lock(&file_priv->prime.lock);
 	obj = drm_gem_object_lookup(file_priv, args->handle);
-	if (!obj)
+	if (!obj) {
+		mutex_unlock(&file_priv->prime.lock);
 		return -ENOENT;
+	}
 
 	if (args->handle == handle) {
 		ret = 0;
-		goto out;
+		goto out_unlock;
 	}
 
-	mutex_lock(&file_priv->prime.lock);
-
 	spin_lock(&file_priv->table_lock);
 	ret = idr_alloc(&file_priv->object_idr, obj, handle, handle + 1,
 			GFP_NOWAIT);
@@ -1051,9 +1050,8 @@ int drm_gem_change_handle_ioctl(struct drm_device *dev, void *data,
 	spin_unlock(&file_priv->table_lock);
 
 out_unlock:
-	mutex_unlock(&file_priv->prime.lock);
-out:
 	drm_gem_object_put(obj);
+	mutex_unlock(&file_priv->prime.lock);
 
 	return ret;
 }
@@ -1085,8 +1083,10 @@ drm_gem_open(struct drm_device *dev, struct drm_file *file_private)
 void
 drm_gem_release(struct drm_device *dev, struct drm_file *file_private)
 {
+	mutex_lock(&file_private->prime.lock);
 	idr_for_each(&file_private->object_idr,
 		     &drm_gem_object_release_handle, file_private);
+	mutex_unlock(&file_private->prime.lock);
 	idr_destroy(&file_private->object_idr);
 }
 
-- 
2.43.0