[PATCH v4] drm/qxl: fix use-after-free in qxl_irq_handler on PCI

[PATCH v4] drm/qxl: fix use-after-free in qxl_irq_handler on PCI

[Óscar Megía López]

Executing below script:

i=0;\
while [ 1 -eq 1 ]; do\
  i=$((i+1)); echo 0000:00:01.0 > /sys/bus/pci/drivers/qxl/unbind;\
  if (($i%1000==0)); then\
      echo loops=$i; free;\
      grep nr_free_pages /proc/vmstat;\
      grep -E "VmallocUsed|Slab|Reclaimable|SUnreclaim" /proc/meminfo;\
      sync; echo 3 > /proc/sys/vm/drop_caches;\
      echo 1 > /proc/sys/vm/compact_memory;\
      udevadm settle;\
      free;\
      grep nr_free_pages /proc/vmstat;\
      grep -E "VmallocUsed|Slab|Reclaimable|SUnreclaim" /proc/meminfo;\
      uptime;\
  fi;\
  echo 0000:00:01.0 > /sys/bus/pci/drivers/qxl/bind;\
done

After a few seconds, it reports:

==================================================================
BUG: KASAN: slab-use-after-free in qxl_irq_handler+0x269/0x2b0
Read of size 8 at addr ffff888001c6cd48 by task swapper/0/0

CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted
     7.1.0-10963-g1a3746ccbb0a #31 PREEMPT(lazy)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
               BIOS Arch Linux 1.17.0-2-2 04/01/2014
Call Trace:
 <IRQ>
 dump_stack_lvl+0x4d/0x70
 print_report+0x14b/0x4b0
 ? __pfx__raw_spin_lock_irqsave+0x10/0x10
 ? profile_tick+0x56/0x90
 ? tick_nohz_handler+0x23c/0x5c0
 kasan_report+0x117/0x140
 ? qxl_irq_handler+0x269/0x2b0
 ? qxl_irq_handler+0x269/0x2b0
 ? __pfx_qxl_irq_handler+0x10/0x10
 qxl_irq_handler+0x269/0x2b0
 ? __pfx_qxl_irq_handler+0x10/0x10
 ? __pfx_qxl_irq_handler+0x10/0x10
 __handle_irq_event_percpu+0x116/0x450
 ? __pfx__raw_spin_lock+0x10/0x10
 handle_irq_event+0xa6/0x1c0
 handle_fasteoi_irq+0x271/0xb10
 ? __pfx_handle_fasteoi_irq+0x10/0x10
 __common_interrupt+0x60/0x130
 common_interrupt+0x7a/0x90
 </IRQ>
 <TASK>
  asm_common_interrupt+0x26/0x40
 RIP: 0010:pv_native_safe_halt+0xf/0x20
 Code: 42 de 00 c3 cc cc cc cc 0f 1f 00 90 90 90 90 90 90 90 90 90
       90 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d a3 cf 20 00
       fb f4 <c3> cc cc cc cc 66 2e 0f 1f 84 00 00 00 00 00 66 90
       90 90 90 90 90
 RSP: 0018:ffffffffb8207e48 EFLAGS: 00000206
 RAX: ffff8880b296f000 RBX: ffffffffb82146c0 RCX: 0000000000000001
 RDX: 0000000000000001 RSI: 0000000000000004 RDI: 0000000000067a04
 RBP: fffffbfff70428d8 R08: ffffffffb7247e1d R09: 1ffff1100d846202
 R10: ffffed100d846203 R11: ffffed100d846203 R12: 0000000000000000
 R13: 0000000000000000 R14: 1ffffffff7040fcd R15: dffffc0000000000
  ? ct_kernel_exit.constprop.0+0x9d/0xc0
  default_idle+0x9/0x10
  default_idle_call+0x37/0x60
  do_idle+0x3a8/0x5d0
  ? __pfx___schedule+0x10/0x10
  ? __pfx_do_idle+0x10/0x10
  cpu_startup_entry+0x4e/0x60
  rest_init+0x11a/0x120
  start_kernel+0x382/0x390
  x86_64_start_reservations+0x24/0x30
  x86_64_start_kernel+0xd6/0xe0
  common_startup_64+0x13e/0x158
  </TASK>

The qxl_pci_remove() function does not call free_irq(), allowing the IRQ
handler to fire after the device has been torn down, accessing freed
memory (qdev->ram_header, qdev->io_base).

Added Disable the device from generating IRQs, Release the IRQ
at the start of qxl_pci_remove() to ensure no IRQs fire
after teardown begins.

Assisted-by: OpenCode:1.17.13-Big Pickle/DeepSeek V4 Flash
Fixes: 48bd85808443 ("drm/qxl: Convert to Linux IRQ interfaces")
Signed-off-by: Óscar Megía López <megia.oscar@gmail.com>
---
Changes in v2:
  - Updated qxl_ttm_init to add ttm_device_fini on error in
    qxl_ttm_init_mem_type.

Changes in v3:
  - Added free_irq on qxl_probe unload.
  - Set to NULL after free on qxl_device_fini and
    added idr_destroy on release_idr and surf_id_idr.
  - Free client_monitors_config.

Changes in v4:
  - Delete all code unnecessary. Leave only code to fix the BUG.
---
 drivers/gpu/drm/qxl/qxl_drv.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/qxl/qxl_drv.c b/drivers/gpu/drm/qxl/qxl_drv.c
index 1e6a2392d7c6..54c1b8a3c723 100644
--- a/drivers/gpu/drm/qxl/qxl_drv.c
+++ b/drivers/gpu/drm/qxl/qxl_drv.c
@@ -155,6 +155,9 @@ qxl_pci_remove(struct pci_dev *pdev)
 {
 	struct drm_device *dev = pci_get_drvdata(pdev);
 
+	disable_irq(pdev->irq);
+	free_irq(pdev->irq, dev);
+
 	drm_kms_helper_poll_fini(dev);
 	drm_dev_unregister(dev);
 	drm_atomic_helper_shutdown(dev);
-- 
2.55.0