From: Michael Bommarito Date: Sat, 2 May 2026 16:43:03 +0000 (-0400) Subject: Bluetooth: HIDP: serialise l2cap_unregister_user via hidp_session_sem X-Git-Tag: v7.1-rc3~26^2~21^2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c5d415596cb6fbdf6334b06cc87a1a5a268d8725;p=thirdparty%2Fkernel%2Fstable.git Bluetooth: HIDP: serialise l2cap_unregister_user via hidp_session_sem Commit dbf666e4fc9b ("Bluetooth: HIDP: Fix possible UAF") made hidp_session_remove() drop the L2CAP reference and set session->conn = NULL once the session is considered removed, and added a bare if (session->conn) guard around the kthread-exit l2cap_unregister_user() call in hidp_session_thread(). The sibling ioctl site in hidp_connection_del() still reads session->conn unlocked and unguarded, and the kthread-exit guard itself is a lockless double-read. hidp_session_find() drops hidp_session_sem before returning, so hidp_session_remove() can null session->conn between the lookup and the call in hidp_connection_del(). Worse, since commit 752a6c9596dd ("Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user") takes mutex_lock(&conn->lock) inside l2cap_unregister_user(), a stale non-NULL snapshot also UAFs on conn->lock. v1 only added an if (session->conn) guard at the ioctl site, which doesn't address either race; Luiz suggested snapshotting session->conn under the sem and clearing it before the call. Taking hidp_session_sem across l2cap_unregister_user() would be wrong: l2cap_conn_del() already establishes the lock order conn->lock -> hidp_session_sem via l2cap_unregister_all_users() -> user->remove == hidp_session_remove(), so taking hidp_session_sem before conn->lock would AB/BA deadlock. Factor a helper hidp_session_unregister_conn() that under down_write(&hidp_session_sem) snapshots session->conn and clears the member, then outside the sem calls l2cap_unregister_user() and l2cap_conn_put() on the snapshot. Call it from both hidp_connection_del() and hidp_session_thread()'s exit path. At most one consumer wins the write-sem; later callers observe session->conn == NULL and skip the unregister and put, so the reference hidp_session_new() took via l2cap_conn_get() is consumed exactly once. session_free() already tolerates a NULL session->conn. Fixes: dbf666e4fc9b ("Bluetooth: HIDP: Fix possible UAF") Suggested-by: Luiz Augusto von Dentz Link: https://lore.kernel.org/all/20260422011437.176643-1-michael.bommarito@gmail.com/ Signed-off-by: Michael Bommarito Assisted-by: Claude:claude-opus-4-7 Signed-off-by: Luiz Augusto von Dentz --- diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c index 7bcf8c5ceaee..976f91eeb745 100644 --- a/net/bluetooth/hidp/core.c +++ b/net/bluetooth/hidp/core.c @@ -1035,6 +1035,28 @@ static struct hidp_session *hidp_session_find(const bdaddr_t *bdaddr) return session; } +/* + * Consume session->conn: clear the member under hidp_session_sem, then + * l2cap_unregister_user() and l2cap_conn_put() the snapshot outside the + * sem. At most one caller wins; later callers see NULL and skip. The + * reference is the one hidp_session_new() took via l2cap_conn_get(). + */ +static void hidp_session_unregister_conn(struct hidp_session *session) +{ + struct l2cap_conn *conn; + + down_write(&hidp_session_sem); + conn = session->conn; + if (conn) + session->conn = NULL; + up_write(&hidp_session_sem); + + if (conn) { + l2cap_unregister_user(conn, &session->user); + l2cap_conn_put(conn); + } +} + /* * Start session synchronously * This starts a session thread and waits until initialization @@ -1311,8 +1333,7 @@ static int hidp_session_thread(void *arg) * Instead, this call has the same semantics as if user-space tried to * delete the session. */ - if (session->conn) - l2cap_unregister_user(session->conn, &session->user); + hidp_session_unregister_conn(session); hidp_session_put(session); @@ -1418,7 +1439,7 @@ int hidp_connection_del(struct hidp_conndel_req *req) HIDP_CTRL_VIRTUAL_CABLE_UNPLUG, NULL, 0); else - l2cap_unregister_user(session->conn, &session->user); + hidp_session_unregister_conn(session); hidp_session_put(session);