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

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

[Bui Viet Dung]

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

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

[patchwork-bot+bluetooth]

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Thu,  8 Oct 2026 12:11:29 +0700 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - Bluetooth: 6lowpan: Pin module for 6lowpan_control debugfs file
    https://git.kernel.org/bluetooth/bluetooth-next/c/b019e48cee2d

You are awesome, thank you!
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