[dm-devel] dm mpath: fix UAF in multipath_message()

[Luo Meng <luomeng12@huawei.com>]

If dm_get_device() create dd in multipath_message(),
and then call table_deps() after dm_put_table_device(),
it will lead to concurrency UAF bugs.

One of the concurrency UAF can be shown as below:

         (USE)                        |    (FREE)
                                      |  target_message
                                      |    multipath_message
                                      |      dm_put_device
                                      |        dm_put_table_device #
                                      |          kfree(td)  # table_device *td
ioctl # DM_TABLE_DEPS_CMD             |         ...
  table_deps                          |         ...
  dm_get_live_or_inactive_table       |         ...
    retrieve_dep                      |         ...
    list_for_each_entry               |         ...
      deps->dev[count++] =            |         ...
          huge_encode_dev             |         ...
          (dd->dm_dev->bdev->bd_dev)  |        list_del(&dd->list)
                                      |        kfree(dd) # dm_dev_internal

The root cause of UAF bugs is that find_device() failed in
dm_get_device() and will create dd and refcount set 1, kfree()
in dm_put_table() is not protected. When td, which there are
still pointers point to, is released, the concurrency UAF bug
will happen.

This patch add a flag to determine whether to create a new dd.

Fixes: 8215d6ec5fee(dm table: remove unused dm_get_device range parameters)
Signed-off-by: Luo Meng <luomeng12@huawei.com>
---
 drivers/md/dm-mpath.c         |  2 +-
 drivers/md/dm-table.c         | 43 +++++++++++++++++++++--------------
 include/linux/device-mapper.h |  2 ++
 3 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 6ed9d2731254..ad63d729ff81 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1995,7 +1995,7 @@ static int multipath_message(struct dm_target *ti, unsigned argc, char **argv,
 		goto out;
 	}
 
-	r = dm_get_device(ti, argv[1], dm_table_get_mode(ti->table), &dev);
+	r = __dm_get_device(ti, argv[1], dm_table_get_mode(ti->table), &dev, false);
 	if (r) {
 		DMWARN("message: error getting device %s",
 		       argv[1]);
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 03541cfc2317..9dbc0ba37ae6 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -339,12 +339,8 @@ dev_t dm_get_dev_t(const char *path)
 }
 EXPORT_SYMBOL_GPL(dm_get_dev_t);
 
-/*
- * Add a device to the list, or just increment the usage count if
- * it's already present.
- */
-int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
-		  struct dm_dev **result)
+int __dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
+		    struct dm_dev **result, bool create_dd)
 {
 	int r;
 	dev_t dev;
@@ -368,19 +364,21 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
 
 	dd = find_device(&t->devices, dev);
 	if (!dd) {
-		dd = kmalloc(sizeof(*dd), GFP_KERNEL);
-		if (!dd)
-			return -ENOMEM;
-
-		if ((r = dm_get_table_device(t->md, dev, mode, &dd->dm_dev))) {
-			kfree(dd);
-			return r;
-		}
+		if (create_dd) {
+			dd = kmalloc(sizeof(*dd), GFP_KERNEL);
+			if (!dd)
+				return -ENOMEM;
 
-		refcount_set(&dd->count, 1);
-		list_add(&dd->list, &t->devices);
-		goto out;
+			if ((r = dm_get_table_device(t->md, dev, mode, &dd->dm_dev))) {
+				kfree(dd);
+				return r;
+			}
 
+			refcount_set(&dd->count, 1);
+			list_add(&dd->list, &t->devices);
+			goto out;
+		} else
+			return -ENODEV;
 	} else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
 		r = upgrade_mode(dd, mode, t->md);
 		if (r)
@@ -391,6 +389,17 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
 	*result = dd->dm_dev;
 	return 0;
 }
+EXPORT_SYMBOL(__dm_get_device);
+
+/*
+ * Add a device to the list, or just increment the usage count if
+ * it's already present.
+ */
+int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
+		  struct dm_dev **result)
+{
+	return __dm_get_device(ti, path, mode, result, true);
+}
 EXPORT_SYMBOL(dm_get_device);
 
 static int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index c2a3758c4aaa..6ea542e18048 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -168,6 +168,8 @@ dev_t dm_get_dev_t(const char *path);
 int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
 		  struct dm_dev **result);
 void dm_put_device(struct dm_target *ti, struct dm_dev *d);
+int __dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
+		    struct dm_dev **result, bool create_dd);
 
 /*
  * Information about a target type
-- 
2.31.1

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