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 have no way to distinguish between a
user decision to set a block_device read-only and the disk being write
protected as a result of the hardware state.
To overcome this we add a third state to the gendisk read-only
policy. This flag is exlusively used when the user forces a struct
block_device read-only via BLKROSET. We currently don't allow
switching ro state in sysfs so the ioctl is the only entry point for
this new state.
In set_disk_ro() we check whether the user override flag is in effect
for a disk before changing read-only state based on the device
settings. This means that devices that have a delay before going
read-write will now be able to clear the read-only state. And devices
where the admin or udev has forced the disk read-only will not cause
the gendisk policy to reflect the mode reported by the device.
Cc: Jeremy Cline <jeremy@xxxxxxxxxx>
Cc: Oleksii Kurochko <olkuroch@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v4.16+
Reported-by: Oleksii Kurochko <olkuroch@xxxxxxxxx>
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@xxxxxxxxxx>
---
I have verified that get_disk_ro() and bdev_read_only() callers all
handle the additional value correctly. Same is true for "ro" in
sysfs.
Note that per-partition ro settings are lost on revalidate. This has
been broken for at least a decade and it will require major surgery to
fix. To my knowledge nobody has complained about being unable to make
partition read-only settings stick through a revalidate. So hopefully
this patch will suffice as a simple fix for stable.
---
block/genhd.c | 13 ++++++++++++-
block/ioctl.c | 3 ++-
drivers/scsi/sd.c | 4 +---
include/linux/genhd.h | 6 ++++++
4 files changed, 21 insertions(+), 5 deletions(-)
diff --git a/block/genhd.c b/block/genhd.c
index 1dd8fd6613b8..e29805bfa989 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1549,11 +1549,22 @@ void set_disk_ro(struct gendisk *disk, int flag)
struct disk_part_iter piter;
struct hd_struct *part;
+ /*
+ * If the user has forced disk read-only with BLKROSET, ignore
+ * any device state change requested by the driver.
+ */
+ if (disk->part0.policy == DISK_POLICY_USER_WRITE_PROTECT)
+ return;
if (disk->part0.policy != flag) {
set_disk_ro_uevent(disk, flag);
disk->part0.policy = flag;
}
-
+ /*
+ * If set_disk_ro() is called from revalidate, all partitions
+ * have already been dropped at this point and thus any
+ * per-partition user setting lost. Each partition will
+ * inherit part0 policy when subsequently re-added.
+ */
disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY);
while ((part = disk_part_iter_next(&piter)))
part->policy = flag;
diff --git a/block/ioctl.c b/block/ioctl.c
index 4825c78a6baa..16c42e1b18c8 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -451,7 +451,8 @@ static int blkdev_roset(struct block_device *bdev, fmode_t mode,
return ret;
if (get_user(n, (int __user *)arg))
return -EFAULT;
- set_device_ro(bdev, n);
+ set_device_ro(bdev, n ? DISK_POLICY_USER_WRITE_PROTECT :
+ DISK_POLICY_WRITABLE);
return 0;
}
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index b2da8a00ec33..9aa409b38765 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..2bef434d4dff 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -150,6 +150,12 @@ enum {
DISK_EVENT_EJECT_REQUEST = 1 << 1, /* eject requested */
};
+enum {
+ DISK_POLICY_WRITABLE = 0, /* Default */
+ DISK_POLICY_DEVICE_WRITE_PROTECT = 1, /* Set by device driver */
+ DISK_POLICY_USER_WRITE_PROTECT = 2, /* Set via BLKROSET */
+};
+
struct disk_part_tbl {
struct rcu_head rcu_head;
int len;
--
2.19.2
