From mboxrd@z Thu Jan 1 00:00:00 1970 From: Samuel Holland Subject: [PATCH 2/3] mailbox: Avoid NULL dereference in mbox_chan_received_data Date: Tue, 27 Feb 2018 20:27:13 -0600 Message-ID: <20180228022714.30068-3-samuel@sholland.org> References: <20180228022714.30068-1-samuel@sholland.org> Return-path: In-Reply-To: <20180228022714.30068-1-samuel@sholland.org> Sender: linux-kernel-owner@vger.kernel.org To: Maxime Ripard , Chen-Yu Tsai , Jassi Brar , Rob Herring Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, Andre Przywara , Samuel Holland List-Id: devicetree@vger.kernel.org If a reception IRQ is pending when a mailbox channel is shut down (for example, if the controller uses threaded interrupts), it is possible for mbox_chan_received_data to be called while chan->cl is NULL. This was found while developing a mailbox controller driver for use with SCPI. The SCPI protocol driver frees its mailbox channel during probing if the SCP firmware does not respond within a specified timeout. In this case, if the SCP firmware takes slightly too long to respond, mbox_chan_received_data races with mbox_free_channel clearing chan->cl. Signed-off-by: Samuel Holland --- drivers/mailbox/mailbox.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c index 674b35f402f5..a0258d8672d5 100644 --- a/drivers/mailbox/mailbox.c +++ b/drivers/mailbox/mailbox.c @@ -152,9 +152,11 @@ static enum hrtimer_restart txdone_hrtimer(struct hrtimer *hrtimer) */ void mbox_chan_received_data(struct mbox_chan *chan, void *mssg) { + struct mbox_client *cl = READ_ONCE(chan->cl); + /* No buffering the received data */ - if (chan->cl->rx_callback) - chan->cl->rx_callback(chan->cl, mssg); + if (cl && cl->rx_callback) + cl->rx_callback(cl, mssg); } EXPORT_SYMBOL_GPL(mbox_chan_received_data); -- 2.13.6