[PATCH] Bluetooth: hci_debugfs: 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, the file_operations defined in
hci_debugfs.c (use_debug_keys_fops, sc_only_mode_fops,
ssp_debug_mode_fops, force_bredr_smp_fops, force_static_address_fops,
force_no_mitm_fops, dut_mode_fops, vendor_diag_fops, and the
DEFINE_QUIRK_ATTRIBUTE macro) 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 bluetooth module. When a userspace
process opens any of these debugfs files, a subsequent controller removal
and module unload (rmmod bluetooth) can succeed while the file descriptor
remains open.

When the userspace process subsequently closes the descriptor,
full_proxy_release() accesses the already unmapped file_operations
structure, triggering a kernel oops in full_proxy_release():

  BUG: unable to handle page fault for address: fffffbfff8056f03
  #PF: supervisor read access in kernel mode
  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+0x115/0x6a0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>

The issue was discovered via manual code audit of
net/bluetooth/hci_debugfs.c and verified on a Linux 7.3-rc6 test VM
with CONFIG_BT=m.

Set .owner = THIS_MODULE on all debugfs file_operations tables in
hci_debugfs.c so that debugfs keeps the module loaded until close has
finished.

Fixes: 0886aea6acd2 ("Bluetooth: Expose debug keys usage setting via debugfs")
Cc: stable@vger.kernel.org
Signed-off-by: Bui Viet Dung <dungvn2345@gmail.com>
---
 net/bluetooth/hci_debugfs.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/bluetooth/hci_debugfs.c b/net/bluetooth/hci_debugfs.c
index 2559fb6324d6..cd5ef398f238 100644
--- a/net/bluetooth/hci_debugfs.c
+++ b/net/bluetooth/hci_debugfs.c
@@ -65,6 +65,7 @@ static ssize_t __name ## _write(struct file *file,			      \
 }									      \
 									      \
 static const struct file_operations __name ## _fops = {			      \
+	.owner		= THIS_MODULE,					      \
 	.open		= simple_open,					      \
 	.read		= __name ## _read,				      \
 	.write		= __name ## _write,				      \
@@ -283,6 +284,7 @@ static ssize_t use_debug_keys_read(struct file *file, char __user *user_buf,
 }
 
 static const struct file_operations use_debug_keys_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= use_debug_keys_read,
 	.llseek		= default_llseek,
@@ -301,6 +303,7 @@ static ssize_t sc_only_mode_read(struct file *file, char __user *user_buf,
 }
 
 static const struct file_operations sc_only_mode_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= sc_only_mode_read,
 	.llseek		= default_llseek,
@@ -437,6 +440,7 @@ static ssize_t ssp_debug_mode_read(struct file *file, char __user *user_buf,
 }
 
 static const struct file_operations ssp_debug_mode_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= ssp_debug_mode_read,
 	.llseek		= default_llseek,
@@ -529,6 +533,7 @@ static ssize_t force_bredr_smp_write(struct file *file,
 }
 
 static const struct file_operations force_bredr_smp_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= force_bredr_smp_read,
 	.write		= force_bredr_smp_write,
@@ -778,6 +783,7 @@ static ssize_t force_static_address_write(struct file *file,
 }
 
 static const struct file_operations force_static_address_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= force_static_address_read,
 	.write		= force_static_address_write,
@@ -1177,6 +1183,7 @@ static ssize_t force_no_mitm_write(struct file *file,
 }
 
 static const struct file_operations force_no_mitm_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= force_no_mitm_read,
 	.write		= force_no_mitm_write,
@@ -1315,6 +1322,7 @@ static ssize_t dut_mode_write(struct file *file, const char __user *user_buf,
 }
 
 static const struct file_operations dut_mode_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= dut_mode_read,
 	.write		= dut_mode_write,
@@ -1371,6 +1379,7 @@ static ssize_t vendor_diag_write(struct file *file, const char __user *user_buf,
 }
 
 static const struct file_operations vendor_diag_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= vendor_diag_read,
 	.write		= vendor_diag_write,
-- 
2.43.0