wifi: mac80211: Pin module for hwflags debugfs file operations

An open debugfs file retains its file_operations pointer in the
debugfs proxy state. However, hwflags_ops in net/mac80211/debugfs.c
has no .owner set to THIS_MODULE.

As a result, full_proxy_open_regular() calls fops_get() which succeeds
without taking a reference to the mac80211 module. When CONFIG_MAC80211=m
and wireless debugfs is enabled, a userspace process can open the
hwflags debugfs file and keep the file descriptor open while the module
is unloaded (rmmod mac80211).

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/mac80211/debugfs.c.

Set .owner = THIS_MODULE on hwflags_ops so that debugfs pins the
module until all open file descriptors have been closed.

Signed-off-by: Bui Viet Dung <dungvn2345@gmail.com>
Link: https://patch.msgid.link/20261008052412.541780-1-dungvn2345@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/debugfs.c

@@ -529,6 +529,7 @@ static ssize_t hwflags_write(struct file *file, const char __user *user_buf,
 }
 
 static const struct file_operations hwflags_ops = {
+	.owner = THIS_MODULE,
 	.open = simple_open,
 	.read = hwflags_read,
 	.write = hwflags_write,