[PATCH v2] sed-opal: allow using IOC_OPAL_SAVE for locking too

[luca.boccassi@gmail.com]

From: Luca Boccassi <bluca@debian.org>

Usually when closing a crypto device (eg: dm-crypt with LUKS) the
volume key is not required, as it requires root privileges anyway, and
root can deny access to a disk in many ways regardless. Requiring the
volume key to lock the device is a peculiarity of the OPAL
specification.

Given we might already have saved the key if the user requested it via
the 'IOC_OPAL_SAVE' ioctl, we can use that key to lock the device if no
key was provided here and the locking range matches, and the user sets
the appropriate flag with 'IOC_OPAL_SAVE'. This allows integrating OPAL
with tools and libraries that are used to the common behaviour and do
not ask for the volume key when closing a device.

Callers can always pass a non-zero key and it will be used regardless,
as before.

Suggested-by: Štěpán Horáček <stepan.horacek@gmail.com>
Signed-off-by: Luca Boccassi <bluca@debian.org>
---
v2: break on 80chr for optimal rendering on 1970s green monochrome monitors
    make the new functionality dependent on a new flag that has to be
    passed to IOC_OPAL_SAVE, using reserved bits in its ioctl struct

 block/sed-opal.c              | 32 ++++++++++++++++++++++++++++++++
 include/uapi/linux/sed-opal.h |  3 ++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/block/sed-opal.c b/block/sed-opal.c
index 9bdb833e5817..3a81754a0fdf 100644
--- a/block/sed-opal.c
+++ b/block/sed-opal.c
@@ -2470,6 +2470,38 @@ static int opal_lock_unlock(struct opal_dev *dev,
 		return -EINVAL;
 
 	mutex_lock(&dev->dev_lock);
+
+	/*
+	 * Usually when closing a crypto device (eg: dm-crypt with LUKS) the volume
+	 * key is not required, as it requires root privileges anyway, and root can
+	 * deny access to a disk in many ways regardless. Requiring the volume key
+	 * to lock the device is a peculiarity of the OPAL specification.
+	 * Given we might already have saved the key if the user requested it via
+	 * the 'IOC_OPAL_SAVE' ioctl, we can use that key to lock the device if no
+	 * key was provided here, the locking range matches and the appropriate
+	 * flag was passed with 'IOC_OPAL_SAVE'. This allows integrating OPAL with
+	 * tools and libraries that are used to the common behaviour and do not ask
+	 * for the volume key when closing a device.
+	 */
+	if (lk_unlk->l_state == OPAL_LK &&
+			lk_unlk->session.opal_key.key_len == 0) {
+		struct opal_suspend_data *iter;
+
+		setup_opal_dev(dev);
+		list_for_each_entry(iter, &dev->unlk_lst, node) {
+			if (iter->unlk.save_for_lock &&
+					iter->lr == lk_unlk->session.opal_key.lr &&
+					iter->unlk.session.opal_key.key_len > 0) {
+				lk_unlk->session.opal_key.key_len =
+					iter->unlk.session.opal_key.key_len;
+				memcpy(lk_unlk->session.opal_key.key,
+					iter->unlk.session.opal_key.key,
+					iter->unlk.session.opal_key.key_len);
+				break;
+			}
+		}
+	}
+
 	ret = __opal_lock_unlock(dev, lk_unlk);
 	mutex_unlock(&dev->dev_lock);
 
diff --git a/include/uapi/linux/sed-opal.h b/include/uapi/linux/sed-opal.h
index 2573772e2fb3..fa604fb07f50 100644
--- a/include/uapi/linux/sed-opal.h
+++ b/include/uapi/linux/sed-opal.h
@@ -76,7 +76,8 @@ struct opal_user_lr_setup {
 struct opal_lock_unlock {
 	struct opal_session_info session;
 	__u32 l_state;
-	__u8 __align[4];
+	__u8 save_for_lock:1; /* if in IOC_OPAL_SAVE will also use key to lock */
+	__u8 __align[3];
 };
 
 struct opal_new_pw {
-- 
2.35.1