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

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

An open debugfs file retains its file_operations pointer in the
debugfs proxy state. However, test_smp_fops in net/bluetooth/smp.c and
test_ecdh_fops in net/bluetooth/selftest.c 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 CONFIG_BT=m
and selftests are enabled, a userspace process can open either
/sys/kernel/debug/bluetooth/selftest_smp or
/sys/kernel/debug/bluetooth/selftest_ecdh and keep the file descriptor
open while the module is unloaded (rmmod bluetooth).

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/smp.c
and net/bluetooth/selftest.c.

Set .owner = THIS_MODULE on test_smp_fops and test_ecdh_fops so that
debugfs keeps the module pinned until the file descriptors are closed.

Fixes: 64dd374eac15 ("Bluetooth: Export SMP selftest result in debugfs")
Fixes: 6de50f9fdb60 ("Bluetooth: Export ECDH selftest result in debugfs")
Cc: stable@vger.kernel.org
Signed-off-by: Bui Viet Dung <dungvn2345@gmail.com>
---
 net/bluetooth/selftest.c | 1 +
 net/bluetooth/smp.c      | 1 +
 2 files changed, 2 insertions(+)

diff --git a/net/bluetooth/selftest.c b/net/bluetooth/selftest.c
index ae5b44bb9d3d..cdfc40e0016b 100644
--- a/net/bluetooth/selftest.c
+++ b/net/bluetooth/selftest.c
@@ -188,6 +188,7 @@ static ssize_t test_ecdh_read(struct file *file, char __user *user_buf,
 }
 
 static const struct file_operations test_ecdh_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= test_ecdh_read,
 	.llseek		= default_llseek,
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 2df303f6a38f..81d255525fe0 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -3696,6 +3696,7 @@ static ssize_t test_smp_read(struct file *file, char __user *user_buf,
 }
 
 static const struct file_operations test_smp_fops = {
+	.owner		= THIS_MODULE,
 	.open		= simple_open,
 	.read		= test_smp_read,
 	.llseek		= default_llseek,
-- 
2.43.0