[PATCH v2] ata: libahci: delete the SW activity blink timer on port stop

[hyunjungg <hj351016@gmail.com>]

From: Hyunjung Ko <hj351016@gmail.com>

The software activity LED support arms a per-EM-port timer (emp->timer,
ahci_sw_activity_blink) from ahci_sw_activity() on I/O, and the timer
callback re-arms itself while the LED is blinking. emp->timer lives in
struct ahci_em_priv inside the port's ahci_port_priv, which is allocated
with devm_kzalloc() and freed when the port is torn down.

ahci_port_stop() never deletes this timer, so when the SW activity LED is
in use and the port is stopped (driver unbind / module unload) while the
blink timer is pending, ahci_sw_activity_blink() runs after
ahci_port_priv has been freed and dereferences the freed ahci_em_priv
(use-after-free).

Shut the timer down in ahci_port_stop() before the port private data is
released; timer_shutdown_sync() also stops the self re-arm. The timers are
only set up (ahci_init_sw_activity()) when ATA_FLAG_SW_ACTIVITY is set, so
gate on that flag and skip slots whose timer was never initialised --
timer_shutdown_sync() on an uninitialised timer trips the debug-object and
lockdep checks. Sweep all EM_MAX_SLOTS em_priv slots rather than the
current links, so a detached Port Multiplier's fan-out timer is not missed.

Not tested on real hardware (needs an AHCI controller with SGPIO
enclosure management and the software activity LED enabled).

Fixes: 18f7ba4c2f4b ("libata/ahci: enclosure management support")
Cc: stable@vger.kernel.org
Signed-off-by: Hyunjung Ko <hj351016@gmail.com>
---
diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index 001a6f5e4172..3f6844acb413 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -2605,9 +2605,32 @@ static void ahci_port_stop(struct ata_port *ap)
 {
 	const char *emsg = NULL;
 	struct ahci_host_priv *hpriv = ap->host->private_data;
+	struct ahci_port_priv *pp = ap->private_data;
 	void __iomem *host_mmio = hpriv->mmio;
 	int rc;
 
+	/*
+	 * The SW activity LED blink timer (emp->timer) is armed from the I/O
+	 * path and re-arms itself, and the ahci_em_priv it lives in is part of
+	 * the devm-allocated ahci_port_priv; shut it down before that is freed
+	 * or it can fire against freed memory.  Only slots whose timer was set
+	 * up by ahci_init_sw_activity() may be touched -- timer_shutdown_sync()
+	 * on a never-initialised timer trips the debug-object/lockdep checks --
+	 * and all EM_MAX_SLOTS slots are swept, not just the current links, so a
+	 * detached Port Multiplier's fan-out timer is not missed.
+	 * timer_shutdown_sync() also stops the self re-arm.
+	 */
+	if (ap->flags & ATA_FLAG_SW_ACTIVITY) {
+		int i;
+
+		for (i = 0; i < EM_MAX_SLOTS; i++) {
+			struct ahci_em_priv *emp = &pp->em_priv[i];
+
+			if (emp->timer.function)
+				timer_shutdown_sync(&emp->timer);
+		}
+	}
+
 	/* de-initialize port */
 	rc = ahci_deinit_port(ap, &emsg);
 	if (rc)
-- 
2.43.0