| Message ID | 20210714111602.24021-1-o.rempel@pengutronix.de |
|---|---|
| State | New |
| Headers | show |
| Series | [v1] can: j1939: j1939_session_deactivate(): clarify lifetime of session object | expand |
On 14.07.2021 13:16:02, Oleksij Rempel wrote: > 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") > Reported-by: Xiaochen Zou <xzou017@ucr.edu> > Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de> Added to linux-can/testing regards, Marc
diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c index cb358646e382..cff9812a5585 100644 --- a/net/can/j1939/transport.c +++ b/net/can/j1939/transport.c @@ -1056,11 +1056,16 @@ 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; }
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") Reported-by: Xiaochen Zou <xzou017@ucr.edu> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de> --- net/can/j1939/transport.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)