[PATCH 5.17 0880/1126] btrfs: harden identification of a stale device

Greg Kroah-Hartman
2022-04-05T10:08:12Z

From: Anand Jain <anand.jain@oracle.com>

[ Upstream commit 770c79fb65506fc7c16459855c3839429f46cb32 ]

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@toxicpanda.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/volumes.c | 45 ++++++++++++++++++++++++++++++++++++++-------
1 file changed, 38 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index b07d382d53a8..24e559d90b6a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -534,15 +534,48 @@ btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
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;
+ dev_t dev_old;
+ dev_t dev_new;
+ int ret;
+
+ /*
+ * 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;
+ ret = lookup_bdev(device_name, &dev_old);
+ kfree(device_name);
+ if (ret)
+ return false;
+
+ ret = lookup_bdev(path, &dev_new);
+ if (ret)
+ return false;
+
+ if (dev_old == dev_new)
+ return true;
+
+ return false;
}

/*
@@ -575,9 +608,7 @@ 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 */
--
2.34.1