linux-kernel - [PATCH 20/24] dm: only call early_lookup

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Date:   Tue, 23 May 2023 09:45:31 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Mike Snitzer <snitzer@...nel.org>,
        Joern Engel <joern@...ybastard.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Pavel Machek <pavel@....cz>, dm-devel@...hat.com,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-mtd@...ts.infradead.org, linux-pm@...r.kernel.org
Subject: [PATCH 20/24] 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@....de>
---
 drivers/md/dm-table.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index e997f4322a9967..c230241a76b374 100644
--- a/drivers/md/dm-table.c
+++ b/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 -ENODEV;
 	}
-- 
2.39.2