Re: [PATCH 1/2] Bluetooth: call sock_hold earlier in sco_conn_del

Hi Marcel,

On 10/9/21 3:36 am, Marcel Holtmann wrote:

Hi Desmond,

quoted

In sco_conn_del, conn->sk is read while holding on to the
sco_conn.lock to avoid races with a socket that could be released
concurrently.

However, in between unlocking sco_conn.lock and calling sock_hold,
it's possible for the socket to be freed, which would cause a
use-after-free write when sock_hold is finally called.

To fix this, the reference count of the socket should be increased
while the sco_conn.lock is still held.

Signed-off-by: Desmond Cheong Zhi Xi <redacted>
---
net/bluetooth/sco.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index b62c91c627e2..4a057f99b60a 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c

@@ -187,10 +187,11 @@ static void sco_conn_del(struct hci_conn *hcon, int err)

	/* Kill socket */
	sco_conn_lock(conn);
	sk = conn->sk;

please add a comment here on why we are doing it.

So sorry for the very delayed response. I was looking through old email 
threads to check if my recently resent patch was still necessary, and 
just realized I missed this email.

This patch was merged into the bluetooth-next tree before your feedback 
came in. Would you still like me to write a separate patch to add the 
requested comment?

Best wishes,
Desmond

quoted

+	if (sk)
+		sock_hold(sk);
	sco_conn_unlock(conn);

	if (sk) {
-		sock_hold(sk);
		lock_sock(sk);
		sco_sock_clear_timer(sk);
		sco_chan_del(sk, err);

Regards

Marcel