From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:41460 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752656AbeBKEdm (ORCPT ); Sat, 10 Feb 2018 23:33:42 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Hou Tao" , "Mike Snitzer" Date: Sun, 11 Feb 2018 04:20:06 +0000 Message-ID: Subject: [PATCH 3.2 34/79] dm: fix race between dm_get_from_kobject() and __dm_destroy() In-Reply-To: Sender: stable-owner@vger.kernel.org List-ID: 3.2.99-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Hou Tao commit b9a41d21dceadf8104812626ef85dc56ee8a60ed upstream. 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. Signed-off-by: Hou Tao Signed-off-by: Mike Snitzer Signed-off-by: Ben Hutchings --- drivers/md/dm.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -2685,11 +2685,15 @@ struct mapped_device *dm_get_from_kobjec 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; }