Commit f4808ca9 authored May 29, 2011 by Milan Broz Committed by Alasdair G Kergon May 29, 2011

dm table: reject devices without request fns



This patch adds a check that a block device has a request function
defined before it is used.  Otherwise, misconfiguration can cause an oops.

Because we are allowing devices with zero size e.g. an offline multipath
device as in commit 2cd54d9b
("dm: allow offline devices") there needs to be an additional check
to ensure devices are initialised.  Some block devices, like a loop
device without a backing file, exist but have no request function.

Reproducer is trivial: dm-mirror on unbound loop device
(no backing file on loop devices)

dmsetup create x --table "0 8 mirror core 2 8 sync 2 /dev/loop0 0 /dev/loop1 0"

and mirror resync will immediatelly cause OOps.

BUG: unable to handle kernel NULL pointer dereference at   (null)
 ? generic_make_request+0x2bd/0x590
 ? kmem_cache_alloc+0xad/0x190
 submit_bio+0x53/0xe0
 ? bio_add_page+0x3b/0x50
 dispatch_io+0x1ca/0x210 [dm_mod]
 ? read_callback+0x0/0xd0 [dm_mirror]
 dm_io+0xbb/0x290 [dm_mod]
 do_mirror+0x1e0/0x748 [dm_mirror]

Signed-off-by: Milan Broz <mbroz@redhat.com>
Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

parent 4c259327

drivers/md/dm-table.c

+17 −0

Original line number	Diff line number	Diff line
		@@ -362,6 +362,7 @@ static void close_dev(struct dm_dev_internal d, struct mapped_device md)
		static int device_area_is_invalid(struct dm_target ti, struct dm_dev dev,
		sector_t start, sector_t len, void *data)
		{
		struct request_queue *q;
		struct queue_limits *limits = data;
		struct block_device *bdev = dev->bdev;
		sector_t dev_size =
		@@ -370,6 +371,22 @@ static int device_area_is_invalid(struct dm_target ti, struct dm_dev dev,
		limits->logical_block_size >> SECTOR_SHIFT;
		char b[BDEVNAME_SIZE];

		/*
		* Some devices exist without request functions,
		* such as loop devices not yet bound to backing files.
		* Forbid the use of such devices.
		*/
		q = bdev_get_queue(bdev);
		if (!q \|\| !q->make_request_fn) {
		DMWARN("%s: %s is not yet initialised: "
		"start=%llu, len=%llu, dev_size=%llu",
		dm_device_name(ti->table->md), bdevname(bdev, b),
		(unsigned long long)start,
		(unsigned long long)len,
		(unsigned long long)dev_size);
		return 1;
		}

		if (!dev_size)
		return 0;

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