drm/virtio: fix memory leak of fence event on execbuffer failure

Overview

In the Linux kernel, the following vulnerability has been resolved:

drm/virtio: fix memory leak of fence event on execbuffer failure

virtio_gpu_execbuffer_ioctl() reserves a DRM event with drm_event_reserve_init() when VIRTGPU_EXECBUF_RING_IDX selects a ring that userspace has enabled polling for. virtio_gpu_init_submit() does this before the BO handles, the command buffer, the syncobj arrays and the in-fence are processed, so every later error path runs with the event already pending, including plain argument validation failures such as an invalid bo_handle or an in-syncobj that carries no fence.

On those paths, virtio_gpu_cleanup_submit() drops the out-fence without cancelling the event. The fence is freed without ever having been emitted, taking the only driver-side pointer to the event with it. Closing the DRM file does not help. drm_events_release() unlinks pending events but deliberately leaves the freeing to the driver's later drm_send_event(), which never runs for an orphaned event, so the allocation is leaked permanently.

Found when fuzzing the virtio driver with Syzkaller:

BUG: memory leak
unreferenced object 0xffff88802c176e80 (size 96):
comm "syz.1.367", pid 10561, jiffies 4294960122
hex dump (first 32 bytes):
	00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	c8 6e 17 2c 80 88 ff ff 00 00 00 00 00 00 00 00  .n.,............
backtrace (crc e1973c6b):
	kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
	slab_post_alloc_hook mm/slub.c:4597 [inline]
	slab_alloc_node mm/slub.c:4917 [inline]
	__kmalloc_cache_noprof+0x49d/0x6f0 mm/slub.c:5485
	_kmalloc_noprof include/linux/slab.h:988 [inline]
	_kzalloc_noprof include/linux/slab.h:1309 [inline]
	virtio_gpu_fence_event_create drivers/gpu/drm/virtio/virtgpu_submit.c:282 [inline]
	virtio_gpu_init_submit drivers/gpu/drm/virtio/virtgpu_submit.c:398 [inline]
	virtio_gpu_execbuffer_ioctl+0xbbf/0x1aa0 drivers/gpu/drm/virtio/virtgpu_submit.c:505
	drm_ioctl_kernel+0x1f4/0x3e0 drivers/gpu/drm/drm_ioctl.c:817
	drm_ioctl+0x5f4/0xc70 drivers/gpu/drm/drm_ioctl.c:914
	vfs_ioctl fs/ioctl.c:51 [inline]
	__do_sys_ioctl fs/ioctl.c:597 [inline]
	__se_sys_ioctl fs/ioctl.c:583 [inline]
	__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
	do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
	do_syscall_64+0x116/0x800 arch/x86/entry/syscall_64.c:94
	entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fix by cancelling and freeing the DRM event on the execbuffer error path before dropping the fence. Clear the fence's event pointer after cancellation so it does not retain a dangling pointer.

Affected

• Linux >= cd7f5ca33585918febe5e2f6dc090a21cfa775b0 < 43bfe2b60c149bf6effda25f245a00509061fa15
• Linux >= cd7f5ca33585918febe5e2f6dc090a21cfa775b0 < 4e333e2336138f4659b1d7a0371c499f80428612
• Linux >= cd7f5ca33585918febe5e2f6dc090a21cfa775b0 < 8fa78900fd24247277c03dc7b8a2864cb12d4340
• Linux >= cd7f5ca33585918febe5e2f6dc090a21cfa775b0 < ae583668f16d41fcc1b54f45848c1b6ac1d6669a
• Linux >= cd7f5ca33585918febe5e2f6dc090a21cfa775b0 < b74aad23d99b279bb34d135795f39a6d8ecdc075
• Linux 5.16

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.