[PATCH] Bluetooth: hci_core: Fix slab-use-after-free in hci_cmd_work

[Szymon Wilczek <swilczek.lx@gmail.com>]

syzbot reported a slab-use-after-free in hci_cmd_work.
The issue is that hci_send_cmd_sync() consumes the skb reference
(either by passing it to the driver which frees it, or by calling
kfree_skb() on error), but the skb might be accessed after the call
in certain configurations or due to race conditions with the freeing
process (e.g. vhci_read).

Explicitly hold a reference to the skb using skb_get() before calling
hci_send_cmd_sync() and release it with kfree_skb() afterwards. This
ensures the skb object remains valid throughout the function call,
regardless of how hci_send_cmd_sync() handles the original reference.

Reported-by: syzbot+4d6b203d625d2f57d4ca@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4d6b203d625d2f57d4ca
Signed-off-by: Szymon Wilczek <swilczek.lx@gmail.com>
---
 net/bluetooth/hci_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 8ccec73dce45..af4ef31295c4 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -4149,7 +4149,10 @@ static void hci_cmd_work(struct work_struct *work)
 		if (!skb)
 			return;
 
+		skb_get(skb);
 		err = hci_send_cmd_sync(hdev, skb);
+		kfree_skb(skb);
+
 		if (err)
 			return;
 
-- 
2.52.0