FAILED: patch "[PATCH] dm: use blkdev_get rather than bdgrab when issuing" failed to apply to 4.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 519049afead4f7c3e6446028c41e99fde958cc04 Mon Sep 17 00:00:00 2001
From: Mike Snitzer <snitzer@redhat.com>
Date: Thu, 22 Feb 2018 13:31:20 -0500
Subject: [PATCH] dm: use blkdev_get rather than bdgrab when issuing
 pass-through ioctl

Otherwise an underlying device's teardown (e.g. SCSI) may race with the
DM ioctl or persistent reservation and result in dereferencing driver
memory that gets freed when the underlying device's final blkdev_put()
occurs.

bdgrab() only increases the refcount for the block_device's inode to
ensure the block_device struct itself will not be freed, but does not
guarantee the block_device will remain associated with the gendisk or
its storage.

Cc: stable@vger.kernel.org # 4.8+
Reported-by: David Jeffery <djeffery@redhat.com>
Suggested-by: David Jeffery <djeffery@redhat.com>
Reviewed-by: Ben Marzinski <bmarzins@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 68136806d365..45328d8b2859 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -458,9 +458,11 @@ static int dm_blk_getgeo(struct block_device *bdev, struct hd_geometry *geo)
 	return dm_get_geometry(md, geo);
 }
 
-static int dm_grab_bdev_for_ioctl(struct mapped_device *md,
-				  struct block_device **bdev,
-				  fmode_t *mode)
+static char *_dm_claim_ptr = "I belong to device-mapper";
+
+static int dm_get_bdev_for_ioctl(struct mapped_device *md,
+				 struct block_device **bdev,
+				 fmode_t *mode)
 {
 	struct dm_target *tgt;
 	struct dm_table *map;
@@ -490,6 +492,10 @@ retry:
 		goto out;
 
 	bdgrab(*bdev);
+	r = blkdev_get(*bdev, *mode, _dm_claim_ptr);
+	if (r < 0)
+		goto out;
+
 	dm_put_live_table(md, srcu_idx);
 	return r;
 
@@ -508,7 +514,7 @@ static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode,
 	struct mapped_device *md = bdev->bd_disk->private_data;
 	int r;
 
-	r = dm_grab_bdev_for_ioctl(md, &bdev, &mode);
+	r = dm_get_bdev_for_ioctl(md, &bdev, &mode);
 	if (r < 0)
 		return r;
 
@@ -528,7 +534,7 @@ static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode,
 
 	r =  __blkdev_driver_ioctl(bdev, mode, cmd, arg);
 out:
-	bdput(bdev);
+	blkdev_put(bdev, mode);
 	return r;
 }
 
@@ -708,14 +714,13 @@ static void dm_put_live_table_fast(struct mapped_device *md) __releases(RCU)
 static int open_table_device(struct table_device *td, dev_t dev,
 			     struct mapped_device *md)
 {
-	static char *_claim_ptr = "I belong to device-mapper";
 	struct block_device *bdev;
 
 	int r;
 
 	BUG_ON(td->dm_dev.bdev);
 
-	bdev = blkdev_get_by_dev(dev, td->dm_dev.mode | FMODE_EXCL, _claim_ptr);
+	bdev = blkdev_get_by_dev(dev, td->dm_dev.mode | FMODE_EXCL, _dm_claim_ptr);
 	if (IS_ERR(bdev))
 		return PTR_ERR(bdev);
 
@@ -3011,7 +3016,7 @@ static int dm_pr_reserve(struct block_device *bdev, u64 key, enum pr_type type,
 	fmode_t mode;
 	int r;
 
-	r = dm_grab_bdev_for_ioctl(md, &bdev, &mode);
+	r = dm_get_bdev_for_ioctl(md, &bdev, &mode);
 	if (r < 0)
 		return r;
 
@@ -3021,7 +3026,7 @@ static int dm_pr_reserve(struct block_device *bdev, u64 key, enum pr_type type,
 	else
 		r = -EOPNOTSUPP;
 
-	bdput(bdev);
+	blkdev_put(bdev, mode);
 	return r;
 }
 
@@ -3032,7 +3037,7 @@ static int dm_pr_release(struct block_device *bdev, u64 key, enum pr_type type)
 	fmode_t mode;
 	int r;
 
-	r = dm_grab_bdev_for_ioctl(md, &bdev, &mode);
+	r = dm_get_bdev_for_ioctl(md, &bdev, &mode);
 	if (r < 0)
 		return r;
 
@@ -3042,7 +3047,7 @@ static int dm_pr_release(struct block_device *bdev, u64 key, enum pr_type type)
 	else
 		r = -EOPNOTSUPP;
 
-	bdput(bdev);
+	blkdev_put(bdev, mode);
 	return r;
 }
 
@@ -3054,7 +3059,7 @@ static int dm_pr_preempt(struct block_device *bdev, u64 old_key, u64 new_key,
 	fmode_t mode;
 	int r;
 
-	r = dm_grab_bdev_for_ioctl(md, &bdev, &mode);
+	r = dm_get_bdev_for_ioctl(md, &bdev, &mode);
 	if (r < 0)
 		return r;
 
@@ -3064,7 +3069,7 @@ static int dm_pr_preempt(struct block_device *bdev, u64 old_key, u64 new_key,
 	else
 		r = -EOPNOTSUPP;
 
-	bdput(bdev);
+	blkdev_put(bdev, mode);
 	return r;
 }
 
@@ -3075,7 +3080,7 @@ static int dm_pr_clear(struct block_device *bdev, u64 key)
 	fmode_t mode;
 	int r;
 
-	r = dm_grab_bdev_for_ioctl(md, &bdev, &mode);
+	r = dm_get_bdev_for_ioctl(md, &bdev, &mode);
 	if (r < 0)
 		return r;
 
@@ -3085,7 +3090,7 @@ static int dm_pr_clear(struct block_device *bdev, u64 key)
 	else
 		r = -EOPNOTSUPP;
 
-	bdput(bdev);
+	blkdev_put(bdev, mode);
 	return r;
 }