[PATCH] vhost-vdpa: fix use-after-free in _compat_vdpa_reset

[Si-Wei Liu <si-wei.liu@oracle.com>]

When the vhost-vdpa device is being closed, vhost_vdpa_cleanup() doesn't
clean up the vqs pointer after free. This could lead to use-after-tree
when _compat_vdpa_reset() tries to access the vqs that are freed already.
Fix is to set vqs pointer to NULL at the end of vhost_vdpa_cleanup()
after getting freed, which is guarded by atomic opened state.

  BUG: unable to handle page fault for address: 00000001005b4af4
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 16a80a067 P4D 0
  Oops: 0000 [#1] PREEMPT SMP NOPTI
  CPU: 4 PID: 40387 Comm: qemu-kvm Not tainted 6.6.0-rc7+ #3
  Hardware name: Dell Inc. PowerEdge R750/0PJ80M, BIOS 1.8.2 09/14/2022
  RIP: 0010:_compat_vdpa_reset.isra.0+0x27/0xb0 [vhost_vdpa]
  Code: 90 90 90 0f 1f 44 00 00 41 55 4c 8d ae 08 03 00 00 41 54 55 48
  89 f5 53 4c 8b a6 00 03 00 00 48 85 ff 74 49 48 8b 07 4c 89 ef <48> 8b
  80 88 45 00 00 48 c1 e8 08 48 83 f0 01 89 c3 e8 73 5e 9b dc
  RSP: 0018:ff73a85762073ba0 EFLAGS: 00010286
  RAX: 00000001005b056c RBX: ff32b13ca6994c68 RCX: 0000000000000002
  RDX: 0000000000000001 RSI: ff32b13c07559000 RDI: ff32b13c07559308
  RBP: ff32b13c07559000 R08: 0000000000000000 R09: ff32b12ca497c0f0
  R10: ff73a85762073c58 R11: 0000000c106f9de3 R12: ff32b12c95b1d050
  R13: ff32b13c07559308 R14: ff32b12d0ddc5100 R15: 0000000000008002
  FS:  00007fec5b8cbf80(0000) GS:ff32b13bbfc80000(0000)
  knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00000001005b4af4 CR3: 000000015644a003 CR4: 0000000000773ee0
  PKRU: 55555554
  Call Trace:
   <TASK>
   ? __die+0x20/0x70
   ? page_fault_oops+0x76/0x170
   ? exc_page_fault+0x65/0x150
   ? asm_exc_page_fault+0x22/0x30
   ? _compat_vdpa_reset.isra.0+0x27/0xb0 [vhost_vdpa]
   vhost_vdpa_open+0x57/0x280 [vhost_vdpa]
   ? __pfx_chrdev_open+0x10/0x10
   chrdev_open+0xc6/0x260
   ? __pfx_chrdev_open+0x10/0x10
   do_dentry_open+0x16e/0x530
   do_open+0x21c/0x400
   path_openat+0x111/0x290
   do_filp_open+0xb2/0x160
   ? __check_object_size.part.0+0x5e/0x140
   do_sys_openat2+0x96/0xd0
   __x64_sys_openat+0x53/0xa0
   do_syscall_64+0x59/0x90
   ? syscall_exit_to_user_mode+0x22/0x40
   ? do_syscall_64+0x69/0x90
   ? syscall_exit_to_user_mode+0x22/0x40
   ? do_syscall_64+0x69/0x90
   ? do_syscall_64+0x69/0x90
   ? syscall_exit_to_user_mode+0x22/0x40
   ? do_syscall_64+0x69/0x90
   ? exc_page_fault+0x65/0x150
   entry_SYSCALL_64_after_hwframe+0x6e/0xd8

Fixes: 10cbf8dfaf93 ("vhost-vdpa: clean iotlb map during reset for older userspace")
Fixes: ac7e98c73c05 ("vhost-vdpa: fix NULL pointer deref in _compat_vdpa_reset")
Reported-by: Lei Yang <leiyang@redhat.com>
Closes: https://lore.kernel.org/all/CAPpAL=yHDqn1AztEcN3MpS8o4M+BL_HVy02FdpiHN7DWd91HwQ@mail.gmail.com/
Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
---
 drivers/vhost/vdpa.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 9a2343c45df0..30df5c58db73 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -1355,6 +1355,7 @@ static void vhost_vdpa_cleanup(struct vhost_vdpa *v)
 	vhost_vdpa_free_domain(v);
 	vhost_dev_cleanup(&v->vdev);
 	kfree(v->vdev.vqs);
+	v->vdev.vqs = NULL;
 }
 
 static int vhost_vdpa_open(struct inode *inode, struct file *filep)
-- 
2.39.3