[PATCH] 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. The 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 - nothing in libahci does - so
when the SW activity LED is in use and the AHCI port is stopped (driver
unbind / module unload) while the blink timer is still 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() for every link's em_priv before
the port private data is released. Because the callback re-arms itself,
use timer_shutdown_sync() so a concurrent re-arm cannot resurrect it.
em_priv entries without an armed timer are zero-initialised, for which
timer_shutdown_sync() is a no-op.

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

Fixes: 365cfa1ed5a3 ("ahci: Move generic code into libahci")
Cc: stable@vger.kernel.org
Signed-off-by: Hyunjung Ko <hj351016@gmail.com>
---
 drivers/ata/libahci.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index 001a6f5..873645c 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -2605,9 +2605,23 @@ 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;
+	struct ata_link *link;
+	struct ahci_em_priv *emp;
 	int rc;
 
+	/*
+	 * The SW activity LED blink timer (emp->timer) is armed from the I/O
+	 * path and re-arms itself; shut it down before the devm-allocated
+	 * ahci_port_priv it lives in is freed, or it can fire against freed
+	 * memory.  timer_shutdown_sync() also stops the self re-arm.
+	 */
+	ata_for_each_link(link, ap, EDGE) {
+		emp = &pp->em_priv[link->pmp];
+		timer_shutdown_sync(&emp->timer);
+	}
+
 	/* de-initialize port */
 	rc = ahci_deinit_port(ap, &emsg);
 	if (rc)
-- 
2.43.0