From 7eef18c0479ba5d9f54fba30cd77c233ebca3eb1 Mon Sep 17 00:00:00 2001 From: Oleksij Rempel Date: Wed, 14 Jul 2021 13:16:02 +0200 Subject: [PATCH] can: j1939: j1939_session_deactivate(): clarify lifetime of session object commit 0c71437dd50dd687c15d8ca80b3b68f10bb21d63 upstream. The j1939_session_deactivate() is decrementing the session ref-count and potentially can free() the session. This would cause use-after-free situation. However, the code calling j1939_session_deactivate() does always hold another reference to the session, so that it would not be free()ed in this code path. This patch adds a comment to make this clear and a WARN_ON, to ensure that future changes will not violate this requirement. Further this patch avoids dereferencing the session pointer as a precaution to avoid use-after-free if the session is actually free()ed. Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol") Link: https://lore.kernel.org/r/20210714111602.24021-1-o.rempel@pengutronix.de Reported-by: Xiaochen Zou Signed-off-by: Oleksij Rempel Signed-off-by: Marc Kleine-Budde Signed-off-by: Greg Kroah-Hartman --- net/can/j1939/transport.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c index c5b54089934f..6571895228f0 100644 --- a/net/can/j1939/transport.c +++ b/net/can/j1939/transport.c @@ -1075,11 +1075,16 @@ static bool j1939_session_deactivate_locked(struct j1939_session *session) static bool j1939_session_deactivate(struct j1939_session *session) { + struct j1939_priv *priv = session->priv; bool active; - j1939_session_list_lock(session->priv); + j1939_session_list_lock(priv); + /* This function should be called with a session ref-count of at + * least 2. + */ + WARN_ON_ONCE(kref_read(&session->kref) < 2); active = j1939_session_deactivate_locked(session); - j1939_session_list_unlock(session->priv); + j1939_session_list_unlock(priv); return active; }