[PATCH] scsi: sd: Keep disk read-only when re-reading partition

[Jeremy Cline]

If the read-only flag is true on a SCSI disk, re-reading the partition
table sets the flag back to false.

To observe this bug, you can run:

1. blockdev --setro /dev/sda
2. blockdev --rereadpt /dev/sda
3. blockdev --getro /dev/sda

This commit reads the disk's old state and combines it with the device
disk-reported state rather than unconditionally marking it as RW.

Reported-by: Li Ning <lining916740672@xxxxxxxxxx>
Signed-off-by: Jeremy Cline <jeremy@xxxxxxxxxx>
---
 drivers/scsi/sd.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index bff21e636ddd..7a3a66a7890f 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2595,6 +2595,7 @@ 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);
@@ -2634,7 +2635,8 @@ sd_read_write_protect_flag(struct scsi_disk *sdkp, unsigned char *buffer)
 		sd_first_printk(KERN_WARNING, sdkp,
 			  "Test WP failed, assume Write Enabled\n");
 	} else {
-		sdkp->write_prot = ((data.device_specific & 0x80) != 0);
+		sdkp->write_prot = ((data.device_specific & 0x80) != 0) ||
+			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",
-- 
2.16.2