Patch "SCSI: Fix NULL pointer dereference in runtime PM" has been added to the 4.1-stable tree

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

SCSI: Fix NULL pointer dereference in runtime PM

to the 4.1-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:
scsi-fix-null-pointer-dereference-in-runtime-pm.patch
and it can be found in the queue-4.1 subdirectory.

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

From: Alan Stern <[email protected]>
Date: Mon, 17 Aug 2015 11:02:42 -0400
Subject: SCSI: Fix NULL pointer dereference in runtime PM
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From: Alan Stern <[email protected]>

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.

---
 drivers/scsi/scsi_pm.c |   22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

@@ -217,15 +217,15 @@ static int sdev_runtime_suspend(struct d
 {
 	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;
 }
 

@@ -248,11 +248,11 @@ static int sdev_runtime_resume(struct de
 	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;
 }
 

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

queue-4.1/scsi-fix-null-pointer-dereference-in-runtime-pm.patch