linux-kernel - [PATCH 3.16.y-ckt 116/130] SCSI: Fix NULL pointer dereference in runtime PM

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Date:	Fri,  4 Sep 2015 14:08:24 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Alan Stern <stern@...land.harvard.edu>,
	James Bottomley <JBottomley@...n.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 116/130] SCSI: Fix NULL pointer dereference in runtime PM

3.16.7-ckt17 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alan Stern <stern@...land.harvard.edu>

commit 49718f0fb8c9af192b33d8af3a2826db04025371 upstream.

The routines in scsi_rpm.c assume that if a runtime-PM callback is
invoked for a SCSI device, it can only mean that the device's driver
has asked the block layer to handle the runtime power management (by
calling blk_pm_runtime_init(), which among other things sets q->dev).

However, this assumption turns out to be wrong for things like the ses
driver.  Normally ses devices are not allowed to do runtime PM, but
userspace can override this setting.  If this happens, the kernel gets
a NULL pointer dereference when blk_post_runtime_resume() tries to use
the uninitialized q->dev pointer.

This patch fixes the problem by calling the block layer's runtime-PM
routines only if the device's driver really does have a runtime-PM
callback routine.  Since ses doesn't define any such callbacks, the
crash won't occur.

This fixes Bugzilla #101371.

Signed-off-by: Alan Stern <stern@...land.harvard.edu>
Reported-by: Stanisław Pitucha <viraptor@...il.com>
Reported-by: Ilan Cohen <ilanco@...il.com>
Tested-by: Ilan Cohen <ilanco@...il.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>
Signed-off-by: James Bottomley <JBottomley@...n.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/scsi/scsi_pm.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
index 7454498c4091..a2dcf6a54ec6 100644
--- a/drivers/scsi/scsi_pm.c
+++ b/drivers/scsi/scsi_pm.c
@@ -219,15 +219,15 @@ static int sdev_runtime_suspend(struct device *dev)
 {
 	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
 	struct scsi_device *sdev = to_scsi_device(dev);
-	int err;
+	int err = 0;
 
-	err = blk_pre_runtime_suspend(sdev->request_queue);
-	if (err)
-		return err;
-	if (pm && pm->runtime_suspend)
+	if (pm && pm->runtime_suspend) {
+		err = blk_pre_runtime_suspend(sdev->request_queue);
+		if (err)
+			return err;
 		err = pm->runtime_suspend(dev);
-	blk_post_runtime_suspend(sdev->request_queue, err);
-
+		blk_post_runtime_suspend(sdev->request_queue, err);
+	}
 	return err;
 }
 
@@ -250,11 +250,11 @@ static int sdev_runtime_resume(struct device *dev)
 	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
 	int err = 0;
 
-	blk_pre_runtime_resume(sdev->request_queue);
-	if (pm && pm->runtime_resume)
+	if (pm && pm->runtime_resume) {
+		blk_pre_runtime_resume(sdev->request_queue);
 		err = pm->runtime_resume(dev);
-	blk_post_runtime_resume(sdev->request_queue, err);
-
+		blk_post_runtime_resume(sdev->request_queue, err);
+	}
 	return err;
 }
 
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