From b9a41d21dceadf8104812626ef85dc56ee8a60ed Mon Sep 17 00:00:00 2001 From: Hou Tao Date: Wed, 1 Nov 2017 15:42:36 +0800 Subject: [PATCH] dm: fix race between dm_get_from_kobject() and __dm_destroy() The following BUG_ON was hit when testing repeat creation and removal of DM devices: kernel BUG at drivers/md/dm.c:2919! CPU: 7 PID: 750 Comm: systemd-udevd Not tainted 4.1.44 Call Trace: [] dm_get_from_kobject+0x34/0x3a [] dm_attr_show+0x2b/0x5e [] ? mutex_lock+0x26/0x44 [] sysfs_kf_seq_show+0x83/0xcf [] kernfs_seq_show+0x23/0x25 [] seq_read+0x16f/0x325 [] kernfs_fop_read+0x3a/0x13f [] __vfs_read+0x26/0x9d [] ? security_file_permission+0x3c/0x44 [] ? rw_verify_area+0x83/0xd9 [] vfs_read+0x8f/0xcf [] ? __fdget_pos+0x12/0x41 [] SyS_read+0x4b/0x76 [] system_call_fastpath+0x12/0x71 The bug can be easily triggered, if an extra delay (e.g. 10ms) is added between the test of DMF_FREEING & DMF_DELETING and dm_get() in dm_get_from_kobject(). To fix it, we need to ensure the test of DMF_FREEING & DMF_DELETING and dm_get() are done in an atomic way, so _minor_lock is used. The other callers of dm_get() have also been checked to be OK: some callers invoke dm_get() under _minor_lock, some callers invoke it under _hash_lock, and dm_start_request() invoke it after increasing md->open_count. Cc: stable@vger.kernel.org Signed-off-by: Hou Tao Signed-off-by: Mike Snitzer --- drivers/md/dm.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/drivers/md/dm.c b/drivers/md/dm.c index adb874c2411b..dcfa1a8c9390 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -2711,11 +2711,15 @@ struct mapped_device *dm_get_from_kobject(struct kobject *kobj) md = container_of(kobj, struct mapped_device, kobj_holder.kobj); - if (test_bit(DMF_FREEING, &md->flags) || - dm_deleting_md(md)) - return NULL; - + spin_lock(&_minor_lock); + if (test_bit(DMF_FREEING, &md->flags) || dm_deleting_md(md)) { + md = NULL; + goto out; + } dm_get(md); +out: + spin_unlock(&_minor_lock); + return md; }