[PATCH] Bluetooth: 6lowpan: Pin module for 6lowpan_control debugfs file

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

An open debugfs file retains lowpan_control_fops in the debugfs proxy
state. However, lowpan_control_fops 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 bluetooth_6lowpan module.

With CONFIG_BT_6LOWPAN=m, a userspace process can keep the debugfs file
descriptor for 6lowpan_control open across module unload
(delete_module / rmmod bluetooth_6lowpan). When the process subsequently
closes the file descriptor, full_proxy_release() accesses the already
freed and unmapped lowpan_control_fops table, causing a kernel page fault
or oops.

The issue was discovered via manual code audit of
net/bluetooth/6lowpan.c.

Set .owner = THIS_MODULE on lowpan_control_fops so that debugfs pins
the module until all open file descriptors have finished.

Fixes: 6b8d4a6a0314 ("Bluetooth: 6LoWPAN: Use connected oriented channel instead of fixed one")
Cc: stable@vger.kernel.org
Signed-off-by: Bui Viet Dung <dungvn2345@gmail.com>
---
 net/bluetooth/6lowpan.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index 30f4afa18bc8..20fb20eea8e7 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -1209,6 +1209,7 @@ static int lowpan_control_open(struct inode *inode, struct file *file)
 }
 
 static const struct file_operations lowpan_control_fops = {
+	.owner		= THIS_MODULE,
 	.open		= lowpan_control_open,
 	.read		= seq_read,
 	.write		= lowpan_control_write,
-- 
2.43.0