[PATCH STABLE 5.4] btrfs: harden identification of a stale device

Anand Jain
2022-09-02T09:10:01Z

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.

CC: stable@vger.kernel.org #5.4
Reported-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/volumes.c | 44 +++++++++++++++++++++++++++++++++++++-------
1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index c7706a769de1..548de841cee5 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -713,15 +713,47 @@ static void pending_bios_fn(struct btrfs_work *work)
run_scheduled_bios(device);
}

-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;
}

/*
@@ -754,9 +786,7 @@ static int btrfs_free_stale_devices(const char *path,
&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 */
--
2.33.1