From 0a21fde3fe39835289f69d2280a68d570f611824 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Tue, 17 Feb 2015 14:30:53 -0500 Subject: dm: fix a race condition in dm_get_md commit 2bec1f4a8832e74ebbe859f176d8a9cb20dd97f4 upstream. 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 Signed-off-by: Mike Snitzer Signed-off-by: Jiri Slaby --- drivers/md/dm.c | 27 ++++++++++----------------- 1 file changed, 10 insertions(+), 17 deletions(-) (limited to 'drivers') diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 2f03e8e10c24..93f3fe443657 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -2375,7 +2375,7 @@ 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); @@ -2386,12 +2386,15 @@ 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: @@ -2399,16 +2402,6 @@ 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) -- cgit v1.2.3