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Subject[PATCH 1/1] dm: add message command to disallow device open
Date
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@chromium.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
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