[PATCH 5.10 74/80] btrfs: harden identification of a stale device

[Greg Kroah-Hartman]

From: Anand Jain <anand.jain@xxxxxxxxxx>

commit 770c79fb65506fc7c16459855c3839429f46cb32 upstream.

Identifying and removing the stale device from the fs_uuids list is done
by btrfs_free_stale_devices().  btrfs_free_stale_devices() in turn
depends on device_path_matched() to check if the device appears in more
than one btrfs_device structure.

The matching of the device happens by its path, the device path. However,
when device mapper is in use, the dm device paths are nothing but a link
to the actual block device, which leads to the device_path_matched()
failing to match.

Fix this by matching the dev_t as provided by lookup_bdev() instead of
plain string compare of the device paths.

Reported-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/btrfs/volumes.c |   44 +++++++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 7 deletions(-)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -540,15 +540,47 @@ error:
 	return ret;
 }
 
-static bool device_path_matched(const char *path, struct btrfs_device *device)
+/*
+ * Check if the device in the path matches the device in the given struct device.
+ *
+ * Returns:
+ *   true  If it is the same device.
+ *   false If it is not the same device or on error.
+ */
+static bool device_matched(const struct btrfs_device *device, const char *path)
 {
-	int found;
+	char *device_name;
+	struct block_device *bdev_old;
+	struct block_device *bdev_new;
+
+	/*
+	 * If we are looking for a device with the matching dev_t, then skip
+	 * device without a name (a missing device).
+	 */
+	if (!device->name)
+		return false;
+
+	device_name = kzalloc(BTRFS_PATH_NAME_MAX, GFP_KERNEL);
+	if (!device_name)
+		return false;
 
 	rcu_read_lock();
-	found = strcmp(rcu_str_deref(device->name), path);
+	scnprintf(device_name, BTRFS_PATH_NAME_MAX, "%s", rcu_str_deref(device->name));
 	rcu_read_unlock();
 
-	return found == 0;
+	bdev_old = lookup_bdev(device_name);
+	kfree(device_name);
+	if (IS_ERR(bdev_old))
+		return false;
+
+	bdev_new = lookup_bdev(path);
+	if (IS_ERR(bdev_new))
+		return false;
+
+	if (bdev_old == bdev_new)
+		return true;
+
+	return false;
 }
 
 /*
@@ -581,9 +613,7 @@ static int btrfs_free_stale_devices(cons
 					 &fs_devices->devices, dev_list) {
 			if (skip_device && skip_device == device)
 				continue;
-			if (path && !device->name)
-				continue;
-			if (path && !device_path_matched(path, device))
+			if (path && !device_matched(device, path))
 				continue;
 			if (fs_devices->opened) {
 				/* for an already deleted device return 0 */