[PATCH] Bluetooth: hci_vhci: Pin module for debugfs file operations

[Bui Viet Dung <dungvn2345@gmail.com>]

An open debugfs file retains its file_operations pointer in the
debugfs proxy state. However, force_suspend_fops, force_wakeup_fops,
aosp_capable_fops, and force_devcoredump_fops have no .owner set to
THIS_MODULE. As a result, full_proxy_open_regular() calls fops_get()
which succeeds without taking a reference to the hci_vhci module.

When userspace opens any of these debugfs files and later closes
the /dev/vhci file descriptor (triggering vhci_release() and
debugfs file removal), the open debugfs file descriptor remains valid
in userspace. Because the module refcount was not incremented,
the hci_vhci module can be unloaded via delete_module (rmmod hci_vhci).

When the userspace process subsequently closes the debugfs file
descriptor, full_proxy_release() accesses the already unmapped
file_operations structure, resulting in a kernel page fault / oops:

  BUG: unable to handle page fault for address: fffffbfff846f18b
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  Oops: Oops: 0000 [#1] SMP KASAN NOPTI
  RIP: 0010:full_proxy_release+0x8e/0x140
  Call Trace:
   <TASK>
   __fput+0x39f/0xa60
   fput_close_sync+0xff/0x200
   __x64_sys_close+0x8c/0xf0
   do_syscall_64+0xc3/0x590
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
   </TASK>
  Modules linked in: ... [last unloaded: hci_vhci(E)]

The issue was discovered via manual code audit of
drivers/bluetooth/hci_vhci.c and verified on a Linux 7.3-rc6 test VM
with CONFIG_BT_VHCI=m by keeping a debugfs file open across controller
teardown and module unload.

Set .owner = THIS_MODULE on all four file_operations structures so that
debugfs pins the module until all file descriptors are closed.

Fixes: 28010791193a ("Bluetooth: vhci: Prevent use-after-free by removing debugfs files early")
Cc: stable@vger.kernel.org
Signed-off-by: Bui Viet Dung <dungvn2345@gmail.com>
---
 drivers/bluetooth/hci_vhci.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/bluetooth/hci_vhci.c b/drivers/bluetooth/hci_vhci.c
index eddb32b30539..8f7db0102b25 100644
--- a/drivers/bluetooth/hci_vhci.c
+++ b/drivers/bluetooth/hci_vhci.c
@@ -155,6 +155,7 @@ static ssize_t force_suspend_write(struct file *file,
 }
 
 static const struct file_operations force_suspend_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= force_suspend_read,
 	.write		= force_suspend_write,
@@ -194,6 +195,7 @@ static ssize_t force_wakeup_write(struct file *file,
 }
 
 static const struct file_operations force_wakeup_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= force_wakeup_read,
 	.write		= force_wakeup_write,
@@ -263,6 +265,7 @@ static ssize_t aosp_capable_write(struct file *file,
 }
 
 static const struct file_operations aosp_capable_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= aosp_capable_read,
 	.write		= aosp_capable_write,
@@ -386,6 +389,7 @@ static ssize_t force_devcd_write(struct file *file, const char __user *user_buf,
 }
 
 static const struct file_operations force_devcoredump_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.write		= force_devcd_write,
 };
-- 
2.43.0