[PATCH v2] scsi: sd: block: Fix regressions in read-only block device handling

["Martin K. Petersen" <martin.petersen@oracle.com>]

Some devices come online in write protected state and switch to
read-write once they are ready to process I/O requests. These devices
broke with commit 20bd1d026aac ("scsi: sd: Keep disk read-only when
re-reading partition") because we had no way to distinguish between a
user decision to set a block_device read-only and the actual hardware
device being write-protected.

Because partitions are dropped and recreated on revalidate we are
unable to persist any user-provided policy in hd_struct. Introduce a
bitmap in struct gendisk to track the user configuration. This bitmap
is updated when BLKROSET is called on a given disk or partition.

A helper function, get_user_ro(), is provided to determine whether the
ioctl has forced read-only state for a given block device. This helper
is used by set_disk_ro() and add_partition() to ensure that both
existing and newly created partitions will get the correct state.

 - If BLKROSET sets a whole disk device read-only, all partitions will
   now end up in a read-only state.

 - If BLKROSET sets a given partition read-only, that partition will
   remain read-only post revalidate.

 - Otherwise both the whole disk device and any partitions will
   reflect the write protect state of the underlying device.

Cc: Jeremy Cline <jeremy@jcline.org>
Cc: Oleksii Kurochko <olkuroch@cisco.com>
Cc: stable@vger.kernel.org # v4.16+
Reported-by: Oleksii Kurochko <olkuroch@cisco.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201221
Fixes: 20bd1d026aac ("scsi: sd: Keep disk read-only when re-reading partition")
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

---

v2:
	- Track user read-only state in a bitmap

	- Work around the regression that caused us to drop user
	  preferences on revalidate
---
 block/genhd.c             | 22 +++++++++++++++++-----
 block/ioctl.c             |  4 ++++
 block/partition-generic.c |  2 +-
 drivers/scsi/sd.c         |  4 +---
 include/linux/genhd.h     |  2 ++
 5 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 1dd8fd6613b8..34667eb1d3cc 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1544,19 +1544,31 @@ void set_device_ro(struct block_device *bdev, int flag)
 
 EXPORT_SYMBOL(set_device_ro);
 
+bool get_user_ro(struct gendisk *disk, unsigned int partno)
+{
+	/* Is the user read-only bit set for the whole disk device? */
+	if (test_bit(0, disk->user_ro_bitmap))
+		return true;
+
+	/* Is the user read-only bit set for this particular partition? */
+	if (test_bit(partno, disk->user_ro_bitmap))
+		return true;
+
+	return false;
+}
+EXPORT_SYMBOL(get_user_ro);
+
 void set_disk_ro(struct gendisk *disk, int flag)
 {
 	struct disk_part_iter piter;
 	struct hd_struct *part;
 
-	if (disk->part0.policy != flag) {
+	if (disk->part0.policy != flag)
 		set_disk_ro_uevent(disk, flag);
-		disk->part0.policy = flag;
-	}
 
-	disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY);
+	disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY_PART0);
 	while ((part = disk_part_iter_next(&piter)))
-		part->policy = flag;
+		part->policy = get_user_ro(disk, part->partno) ?: flag;
 	disk_part_iter_exit(&piter);
 }
 
diff --git a/block/ioctl.c b/block/ioctl.c
index 4825c78a6baa..41206df89485 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -451,6 +451,10 @@ static int blkdev_roset(struct block_device *bdev, fmode_t mode,
 		return ret;
 	if (get_user(n, (int __user *)arg))
 		return -EFAULT;
+	if (n)
+		set_bit(bdev->bd_partno, bdev->bd_disk->user_ro_bitmap);
+	else
+		clear_bit(bdev->bd_partno, bdev->bd_disk->user_ro_bitmap);
 	set_device_ro(bdev, n);
 	return 0;
 }
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 8e596a8dff32..c6a3c21c2496 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -338,7 +338,7 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
 		queue_limit_discard_alignment(&disk->queue->limits, start);
 	p->nr_sects = len;
 	p->partno = partno;
-	p->policy = get_disk_ro(disk);
+	p->policy = get_user_ro(disk, partno) ?: get_disk_ro(disk);
 
 	if (info) {
 		struct partition_meta_info *pinfo = alloc_part_info(disk);
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 67cc439b86e4..5dfe37b08d3b 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2591,10 +2591,8 @@ sd_read_write_protect_flag(struct scsi_disk *sdkp, unsigned char *buffer)
 	int res;
 	struct scsi_device *sdp = sdkp->device;
 	struct scsi_mode_data data;
-	int disk_ro = get_disk_ro(sdkp->disk);
 	int old_wp = sdkp->write_prot;
 
-	set_disk_ro(sdkp->disk, 0);
 	if (sdp->skip_ms_page_3f) {
 		sd_first_printk(KERN_NOTICE, sdkp, "Assuming Write Enabled\n");
 		return;
@@ -2632,7 +2630,7 @@ sd_read_write_protect_flag(struct scsi_disk *sdkp, unsigned char *buffer)
 			  "Test WP failed, assume Write Enabled\n");
 	} else {
 		sdkp->write_prot = ((data.device_specific & 0x80) != 0);
-		set_disk_ro(sdkp->disk, sdkp->write_prot || disk_ro);
+		set_disk_ro(sdkp->disk, sdkp->write_prot);
 		if (sdkp->first_scan || old_wp != sdkp->write_prot) {
 			sd_printk(KERN_NOTICE, sdkp, "Write Protect is %s\n",
 				  sdkp->write_prot ? "on" : "off");
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 06c0fd594097..9645c2604465 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -194,6 +194,7 @@ struct gendisk {
 	 */
 	struct disk_part_tbl __rcu *part_tbl;
 	struct hd_struct part0;
+	DECLARE_BITMAP(user_ro_bitmap, DISK_MAX_PARTS);
 
 	const struct block_device_operations *fops;
 	struct request_queue *queue;
@@ -433,6 +434,7 @@ extern struct block_device *bdget_disk(struct gendisk *disk, int partno);
 
 extern void set_device_ro(struct block_device *bdev, int flag);
 extern void set_disk_ro(struct gendisk *disk, int flag);
+extern bool get_user_ro(struct gendisk *disk, unsigned int partno);
 
 static inline int get_disk_ro(struct gendisk *disk)
 {
-- 
2.19.2