From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754776AbbIBNMf (ORCPT ); Wed, 2 Sep 2015 09:12:35 -0400 Received: from devils.ext.ti.com ([198.47.26.153]:49135 "EHLO devils.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753894AbbIBNMe (ORCPT ); Wed, 2 Sep 2015 09:12:34 -0400 From: Felipe Balbi To: James Morris CC: , , , Linux OMAP Mailing List , Felipe Balbi Subject: [PATCH v2] security: device_cgroup: fix RCU lockdep splat Date: Wed, 2 Sep 2015 08:12:28 -0500 Message-ID: <1441199548-29633-1-git-send-email-balbi@ti.com> X-Mailer: git-send-email 2.5.0 In-Reply-To: <20150902125608.GA8299@saruman.tx.rr.com> References: <20150902125608.GA8299@saruman.tx.rr.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org while booting AM437x device, the following splat triggered: [ 12.005238] =============================== [ 12.009749] [ INFO: suspicious RCU usage. ] [ 12.014116] 4.2.0-next-20150831 #1154 Not tainted [ 12.019050] ------------------------------- [ 12.023408] security/device_cgroup.c:405 device_cgroup:verify_new_ex called without proper synchronization! [ 12.033576] other info that might help us debug this: [ 12.041942] rcu_scheduler_active = 1, debug_locks = 0 [ 12.048796] 4 locks held by systemd/1: [ 12.052700] #0: (sb_writers#7){.+.+.+}, at: [] __sb_start_write+0x8c/0xb0 [ 12.060954] #1: (&of->mutex){+.+.+.}, at: [] kernfs_fop_write+0x50/0x1b8 [ 12.069085] #2: (s_active#30){++++.+}, at: [] kernfs_fop_write+0x58/0x1b8 [ 12.077310] #3: (devcgroup_mutex){+.+...}, at: [] devcgroup_access_write+0x20/0x658 [ 12.086575] stack backtrace: [ 12.091124] CPU: 0 PID: 1 Comm: systemd Not tainted 4.2.0-next-20150831 #1154 [ 12.098609] Hardware name: Generic AM43 (Flattened Device Tree) [ 12.104807] [] (unwind_backtrace) from [] (show_stack+0x10/0x14) [ 12.112924] [] (show_stack) from [] (dump_stack+0x84/0x9c) [ 12.120491] [] (dump_stack) from [] (verify_new_ex+0xc4/0xdc) [ 12.128326] [] (verify_new_ex) from [] (devcgroup_access_write+0x374/0x658) [ 12.137426] [] (devcgroup_access_write) from [] (cgroup_file_write+0x28/0x1bc) [ 12.146796] [] (cgroup_file_write) from [] (kernfs_fop_write+0xc0/0x1b8) [ 12.155620] [] (kernfs_fop_write) from [] (__vfs_write+0x1c/0xd8) [ 12.163783] [] (__vfs_write) from [] (vfs_write+0x90/0x16c) [ 12.171426] [] (vfs_write) from [] (SyS_write+0x44/0x9c) [ 12.178806] [] (SyS_write) from [] (ret_fast_syscall+0x0/0x1c) Fix it by making sure rcu_read_lock() is held around calls to parent_has_perm(). Signed-off-by: Felipe Balbi --- Changes since v1: - move rcu_read_lock/unlock to wrap parent_has_perm() security/device_cgroup.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/security/device_cgroup.c b/security/device_cgroup.c index 73455089feef..dd77ed206fa4 100644 --- a/security/device_cgroup.c +++ b/security/device_cgroup.c @@ -608,6 +608,7 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, int count, rc = 0; struct dev_exception_item ex; struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent); + int ret; if (!capable(CAP_SYS_ADMIN)) return -EPERM; @@ -734,7 +735,11 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, break; } - if (!parent_has_perm(devcgroup, &ex)) + rcu_read_lock(); + ret = parent_has_perm(devcgroup, &ex); + rcu_read_unlock(); + + if (!ret) return -EPERM; rc = dev_exception_add(devcgroup, &ex); break; -- 2.5.0