7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Pauli Virtanen [ Upstream commit 86b55991d3cd690e73c5ef8d20b75ae4905b357a ] l2cap_chan may be linked to l2cap_conn at most once. This is assumed in several places, eg l2cap_chan_del cleanup. There is a TOCTOU race where the invariant is violated: [Task 1] [Task 2] l2cap_chan_connect l2cap_sock_bind l2cap_chan_lock lock_sock l2cap_state_change if (sk->sk_state != BT_OPEN) chan->state = BT_CONNECT l2cap_sock_state_change_cb chan->state = BT_BOUND sk->sk_state = BT_BOUND lock_sock <------------------ release_sock sk->sk_state = BT_CONNECT l2cap_sock_connect() does not check sk->sk_state, so since chan->state is now BT_BOUND, subsequent connect() ends up with second __l2cap_chan_add. Explicitly document and check the invariant in __l2cap_chan_add with WARN_ON_ONCE. The only callsite where it could be hit is l2cap_chan_connect, so add pre-check there to avoid relying on chan->state. chan->state read/write is not properly guarded currently so there can be other TOCTOUC problems. Add l2cap_lock_chan in l2cap_sock_bind() to guard chan->state write. Fixes: b66774b48dd9 ("Bluetooth: L2CAP: Fix UAF in channel timeout by holding conn ref") Assisted-by: deepseek-4-flash # finding the race condition Signed-off-by: Pauli Virtanen Signed-off-by: Luiz Augusto von Dentz Signed-off-by: Sasha Levin --- net/bluetooth/l2cap_core.c | 7 ++++++- net/bluetooth/l2cap_sock.c | 2 ++ 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index aaa2a1cd489a5..d87d2dfbce684 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -622,6 +622,10 @@ void __l2cap_chan_add(struct l2cap_conn *conn, struct l2cap_chan *chan) BT_DBG("conn %p, psm 0x%2.2x, dcid 0x%4.4x", conn, __le16_to_cpu(chan->psm), chan->dcid); + /* Caller must ensure l2cap_chan is linked to l2cap_conn only once */ + if (WARN_ON_ONCE(chan->conn || test_bit(FLAG_DEL, &chan->flags))) + return; + conn->disc_reason = HCI_ERROR_REMOTE_USER_TERM; chan->conn = l2cap_conn_get(conn); @@ -7416,7 +7420,8 @@ int l2cap_chan_connect(struct l2cap_chan *chan, __le16 psm, u16 cid, } } - if (cid && __l2cap_get_chan_by_dcid(conn, cid)) { + if ((cid && __l2cap_get_chan_by_dcid(conn, cid)) || chan->conn || + test_bit(FLAG_DEL, &chan->flags)) { hci_conn_drop(hcon); err = -EBUSY; goto chan_unlock; diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c index 1194c37e466f1..38aedd7b00d33 100644 --- a/net/bluetooth/l2cap_sock.c +++ b/net/bluetooth/l2cap_sock.c @@ -109,6 +109,7 @@ static int l2cap_sock_bind(struct socket *sock, struct sockaddr_unsized *addr, i return -EINVAL; } + l2cap_chan_lock(chan); lock_sock(sk); if (sk->sk_state != BT_OPEN) { @@ -174,6 +175,7 @@ static int l2cap_sock_bind(struct socket *sock, struct sockaddr_unsized *addr, i done: release_sock(sk); + l2cap_chan_unlock(chan); return err; } -- 2.53.0