dm: only call early_lookup_bdev from early boot context

early_lookup_bdev is supposed to only be called from the early boot
code, but dm_get_device calls it as a general fallback when lookup_bdev
fails, which is problematic because early_lookup_bdev bypasses all normal
path based permission checking, and might cause problems with certain
container environments renaming devices.

Switch to only call early_lookup_bdev when dm is built-in and the system
state in not running yet.  This means it is still available when tables
are constructed by dm-init.c from the kernel command line, but not
otherwise.

Note that this strictly speaking changes the kernel ABI as the PARTUUID=
and PARTLABEL= style syntax is now not available during a running
systems.  They never were intended for that, but this breaks things
we'll have to figure out a way to make them available again.  But if
avoidable in any way I'd rather avoid that.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
Link: https://lore.kernel.org/r/20230531125535.676098-21-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/dm-table.c

@@ -326,8 +326,11 @@ static int upgrade_mode(struct dm_dev_internal *dd, fmode_t new_mode,
 /*
  * Add a device to the list, or just increment the usage count if
  * it's already present.
+ *
+ * Note: the __ref annotation is because this function can call the __init
+ * marked early_lookup_bdev when called during early boot code from dm-init.c.
  */
-int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
+int __ref dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
 		  struct dm_dev **result)
 {
 	int r;
@@ -346,8 +349,10 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
 			return -EOVERFLOW;
 	} else {
 		r = lookup_bdev(path, &dev);
-		if (r)
+#ifndef MODULE
+		if (r && system_state < SYSTEM_RUNNING)
 			r = early_lookup_bdev(path, &dev);
+#endif
 		if (r)
 			return r;
 	}