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dm: fix a race condition in dm_get_md 

The function dm_get_md finds a device mapper device with a given dev_t,
increases the reference count and returns the pointer.

dm_get_md calls dm_find_md, dm_find_md takes _minor_lock, finds the
device, tests that the device doesn't have DMF_DELETING or DMF_FREEING
flag, drops _minor_lock and returns pointer to the device. dm_get_md then
calls dm_get. dm_get calls BUG if the device has the DMF_FREEING flag,
otherwise it increments the reference count.

There is a possible race condition - after dm_find_md exits and before
dm_get is called, there are no locks held, so the device may disappear or
DMF_FREEING flag may be set, which results in BUG.

To fix this bug, we need to call dm_get while we hold _minor_lock. This
patch renames dm_find_md to dm_get_md and changes it so that it calls
dm_get while holding the lock.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
hifive-unleashed-5.1
Mikulas Patocka 2015-02-17 14:30:53 -05:00 committed by Mike Snitzer
parent b3c5fd3052
commit 2bec1f4a88
1 changed files with 10 additions and 17 deletions
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27
drivers/md/dm.c
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@ -2571,7 +2571,7 @@ int dm_setup_md_queue(struct mapped_device *md)
return 0;
}
static struct mapped_device *dm_find_md(dev_t dev)
struct mapped_device *dm_get_md(dev_t dev)
{
struct mapped_device *md;
unsigned minor = MINOR(dev);
@ -2582,12 +2582,15 @@ static struct mapped_device *dm_find_md(dev_t dev)
spin_lock(&_minor_lock);
md = idr_find(&_minor_idr, minor);
if (md && (md == MINOR_ALLOCED ||
(MINOR(disk_devt(dm_disk(md))) != minor) ||
dm_deleting_md(md) ||
test_bit(DMF_FREEING, &md->flags))) {
md = NULL;
goto out;
if (md) {
if ((md == MINOR_ALLOCED ||
(MINOR(disk_devt(dm_disk(md))) != minor) ||
dm_deleting_md(md) ||
test_bit(DMF_FREEING, &md->flags))) {
md = NULL;
goto out;
}
dm_get(md);
}
out:
@ -2595,16 +2598,6 @@ out:
return md;
}
struct mapped_device *dm_get_md(dev_t dev)
{
struct mapped_device *md = dm_find_md(dev);
if (md)
dm_get(md);
return md;
}
EXPORT_SYMBOL_GPL(dm_get_md);
void *dm_get_mdptr(struct mapped_device *md)