Patch "serial: samsung: Fix ERR pointer dereference on deferred probe" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

serial: samsung: Fix ERR pointer dereference on deferred probe

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
serial-samsung-fix-err-pointer-dereference-on-deferred-probe.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Krzysztof Kozlowski <[email protected]>
Date: Thu, 16 Jun 2016 08:27:35 +0200
Subject: serial: samsung: Fix ERR pointer dereference on deferred probe

From: Krzysztof Kozlowski <[email protected]>

commit e51e4d8a185de90424b03f30181b35f29c46a25a upstream.

When the clk_get() of "uart" clock returns EPROBE_DEFER, the next re-probe finishes with success but uses invalid (ERR_PTR) values. This leads to dereferencing of ERR_PTR stored under ourport->clk:

	12c30000.serial: Controller clock not found
	(...)
	12c30000.serial: ttySAC3 at MMIO 0x12c30000 (irq = 61, base_baud = 0) is a S3C6400/10
	Unable to handle kernel paging request at virtual address fffffdfb

	(clk_prepare) from [<c039f7d0>] (s3c24xx_serial_pm+0x20/0x128)
	(s3c24xx_serial_pm) from [<c0395414>] (uart_change_pm+0x38/0x40)
	(uart_change_pm) from [<c039689c>] (uart_add_one_port+0x31c/0x44c)
	(uart_add_one_port) from [<c03a035c>] (s3c24xx_serial_probe+0x2a8/0x418)
	(s3c24xx_serial_probe) from [<c03ee110>] (platform_drv_probe+0x50/0xb0)
	(platform_drv_probe) from [<c03ecb44>] (driver_probe_device+0x1f4/0x2b0)
	(driver_probe_device) from [<c03eb0c0>] (bus_for_each_drv+0x44/0x8c)
	(bus_for_each_drv) from [<c03ec8c8>] (__device_attach+0x9c/0x100)
	(__device_attach) from [<c03ebf54>] (bus_probe_device+0x84/0x8c)
	(bus_probe_device) from [<c03ec388>] (deferred_probe_work_func+0x60/0x8c)
	(deferred_probe_work_func) from [<c012fee4>] (process_one_work+0x120/0x328)
	(process_one_work) from [<c0130150>] (worker_thread+0x2c/0x4ac)
	(worker_thread) from [<c0135320>] (kthread+0xd8/0xf4)
	(kthread) from [<c0107978>] (ret_from_fork+0x14/0x3c)

The first unsuccessful clk_get() causes s3c24xx_serial_init_port() to exit with failure but the s3c24xx_uart_port is left half-configured (e.g. port->mapbase is set, clk contains ERR_PTR). On next re-probe, the function s3c24xx_serial_init_port() will exit early with success because of configured port->mapbase and driver will use old values, including the ERR_PTR as clock.

Fix this by cleaning the port->mapbase on error path so each re-probe will initialize all of the port settings.

---
 drivers/tty/serial/samsung.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

@@ -1684,7 +1684,7 @@ static int s3c24xx_serial_init_port(stru
 		return -ENODEV;
 
 	if (port->mapbase != 0)
-		return 0;
+		return -EINVAL;
 
 	/* setup info for port */
 	port->dev	= &platdev->dev;

@@ -1738,22 +1738,25 @@ static int s3c24xx_serial_init_port(stru
 		ourport->dma = devm_kzalloc(port->dev,
 					    sizeof(*ourport->dma),
 					    GFP_KERNEL);
-		if (!ourport->dma)
-			return -ENOMEM;
+		if (!ourport->dma) {
+			ret = -ENOMEM;
+			goto err;
+		}
 	}
 
 	ourport->clk	= clk_get(&platdev->dev, "uart");
 	if (IS_ERR(ourport->clk)) {
 		pr_err("%s: Controller clock not found\n",
 				dev_name(&platdev->dev));
-		return PTR_ERR(ourport->clk);
+		ret = PTR_ERR(ourport->clk);
+		goto err;
 	}
 
 	ret = clk_prepare_enable(ourport->clk);
 	if (ret) {
 		pr_err("uart: clock failed to prepare+enable: %d\n", ret);
 		clk_put(ourport->clk);
-		return ret;
+		goto err;
 	}
 
 	/* Keep all interrupts masked and cleared */

@@ -1769,7 +1772,12 @@ static int s3c24xx_serial_init_port(stru
 
 	/* reset the fifos (and setup the uart) */
 	s3c24xx_serial_resetport(port, cfg);
+
 	return 0;
+
+err:
+	port->mapbase = 0;
+	return ret;
 }
 
 /* Device driver serial port probe */

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/serial-samsung-fix-err-pointer-dereference-on-deferred-probe.patch