linux-kernel - [PATCH 1/1] dm: add message command to disallow device open

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Message-Id: <20220704100221.1.I15b3f7a84ba5a97fde9276648e391b54957103ff@changeid>
Date:   Mon,  4 Jul 2022 10:02:25 +1000
From:   Daniil Lunev <dlunev@...omium.org>
To:     Alasdair Kergon <agk@...hat.com>
Cc:     Brian Geffon <bgeffon@...gle.com>,
        Daniil Lunev <dlunev@...omium.org>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] dm: add message command to disallow device open

A message can be passed to device mapper to prohibit open on a certain
mapped device. This makes possible to disallow userspace access to
raw swapped data if the system uses device mapper to encrypt it at rest.

Signed-off-by: Daniil Lunev <dlunev@...omium.org>
---

 drivers/md/dm-core.h          |  1 +
 drivers/md/dm-ioctl.c         | 10 ++++++++++
 drivers/md/dm.c               | 12 ++++++++++++
 drivers/md/dm.h               | 10 ++++++++++
 include/uapi/linux/dm-ioctl.h |  5 +++++
 5 files changed, 38 insertions(+)

diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index 4277853c75351..37529b605b7c4 100644
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -140,6 +140,7 @@ struct mapped_device {
 #define DMF_SUSPENDED_INTERNALLY 7
 #define DMF_POST_SUSPENDING 8
 #define DMF_EMULATE_ZONE_APPEND 9
+#define DMF_DISALLOW_OPEN 10
 
 void disable_discard(struct mapped_device *md);
 void disable_write_zeroes(struct mapped_device *md);
diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 87310fceb0d86..e35d560aa2ff3 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -815,6 +815,9 @@ static void __dev_status(struct mapped_device *md, struct dm_ioctl *param)
 	if (dm_test_deferred_remove_flag(md))
 		param->flags |= DM_DEFERRED_REMOVE;
 
+	if (dm_test_disallow_open_flag(md))
+		param->flags |= DM_DISALLOWED_OPEN;
+
 	param->dev = huge_encode_dev(disk_devt(disk));
 
 	/*
@@ -1656,6 +1659,13 @@ static int message_for_md(struct mapped_device *md, unsigned argc, char **argv,
 		}
 		return dm_cancel_deferred_remove(md);
 	}
+	if (!strcasecmp(argv[0], "@disallow_open")) {
+		if (argc != 1) {
+			DMERR("Invalid arguments for @disallow_open");
+			return -EINVAL;
+		}
+		return dm_disallow_open(md);
+	}
 
 	r = dm_stats_message(md, argc, argv, result, maxlen);
 	if (r < 2)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 82957bd460e89..3e53d1bd40f0c 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -327,6 +327,7 @@ static int dm_blk_open(struct block_device *bdev, fmode_t mode)
 		goto out;
 
 	if (test_bit(DMF_FREEING, &md->flags) ||
+	    test_bit(DMF_DISALLOW_OPEN, &md->flags) ||
 	    dm_deleting_md(md)) {
 		md = NULL;
 		goto out;
@@ -403,6 +404,12 @@ int dm_cancel_deferred_remove(struct mapped_device *md)
 	return r;
 }
 
+int dm_disallow_open(struct mapped_device *md)
+{
+	set_bit(DMF_DISALLOW_OPEN, &md->flags);
+	return 0;
+}
+
 static void do_deferred_remove(struct work_struct *w)
 {
 	dm_deferred_remove();
@@ -2883,6 +2890,11 @@ int dm_test_deferred_remove_flag(struct mapped_device *md)
 	return test_bit(DMF_DEFERRED_REMOVE, &md->flags);
 }
 
+int dm_test_disallow_open_flag(struct mapped_device *md)
+{
+	return test_bit(DMF_DISALLOW_OPEN, &md->flags);
+}
+
 int dm_suspended(struct dm_target *ti)
 {
 	return dm_suspended_md(ti->table->md);
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 9013dc1a7b002..da27f9dfe1413 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -163,6 +163,16 @@ int dm_test_deferred_remove_flag(struct mapped_device *md);
  */
 void dm_deferred_remove(void);
 
+/*
+ * Test if the device is openable.
+ */
+int dm_test_disallow_open_flag(struct mapped_device *md);
+
+/*
+ * Prevent new open request on the device.
+ */
+int dm_disallow_open(struct mapped_device *md);
+
 /*
  * The device-mapper can be driven through one of two interfaces;
  * ioctl or filesystem, depending which patch you have applied.
diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index 2e9550fef90fa..3b4d12d09c005 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -382,4 +382,9 @@ enum {
  */
 #define DM_IMA_MEASUREMENT_FLAG	(1 << 19) /* In */
 
+/*
+ * If set, the device can not be opened.
+ */
+#define DM_DISALLOWED_OPEN	(1 << 20) /* Out */
+
 #endif				/* _LINUX_DM_IOCTL_H */
-- 
2.31.0