Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759207Ab2JKSzp (ORCPT ); Thu, 11 Oct 2012 14:55:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:2729 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756148Ab2JKSzm (ORCPT ); Thu, 11 Oct 2012 14:55:42 -0400 Date: Thu, 11 Oct 2012 14:55:36 -0400 From: Vivek Goyal To: "Jun'ichi Nomura" Cc: Tejun Heo , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] Fix use-after-free of q->root_blkg and q->root_rl.blkg Message-ID: <20121011185536.GE28268@redhat.com> References: <50750367.2070508@ce.jp.nec.com> <20121010155929.GA18733@redhat.com> <50762182.5090806@ce.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50762182.5090806@ce.jp.nec.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4008 Lines: 95 On Thu, Oct 11, 2012 at 10:31:46AM +0900, Jun'ichi Nomura wrote: [..] > Below is the updated version of the patch. > > ====================================================================== > blk_put_rl() does not call blkg_put() for q->root_rl because we > don't take request list reference on q->root_blkg. > However, if root_blkg is once attached then detached (freed), > blk_put_rl() is confused by the bogus pointer in q->root_blkg. > > For example, with !CONFIG_BLK_DEV_THROTTLING && CONFIG_CFQ_GROUP_IOSCHED, > switching IO scheduler from cfq to deadline will cause system stall > after the following warning with 3.6: > > > WARNING: at /work/build/linux/block/blk-cgroup.h:250 blk_put_rl+0x4d/0x95() > > Modules linked in: bridge stp llc sunrpc acpi_cpufreq freq_table mperf ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4 > > Pid: 0, comm: swapper/0 Not tainted 3.6.0 #1 > > Call Trace: > > [] warn_slowpath_common+0x85/0x9d > > [] warn_slowpath_null+0x1a/0x1c > > [] blk_put_rl+0x4d/0x95 > > [] __blk_put_request+0xc3/0xcb > > [] blk_finish_request+0x232/0x23f > > [] ? blk_end_bidi_request+0x34/0x5d > > [] blk_end_bidi_request+0x42/0x5d > > [] blk_end_request+0x10/0x12 > > [] scsi_io_completion+0x207/0x4d5 > > [] scsi_finish_command+0xfa/0x103 > > [] scsi_softirq_done+0xff/0x108 > > [] blk_done_softirq+0x8d/0xa1 > > [] ? generic_smp_call_function_single_interrupt+0x9f/0xd7 > > [] __do_softirq+0x102/0x213 > > [] ? lock_release_holdtime+0xb6/0xbb > > [] ? raise_softirq_irqoff+0x9/0x3d > > [] call_softirq+0x1c/0x30 > > [] do_softirq+0x4b/0xa3 > > [] irq_exit+0x53/0xd5 > > [] smp_call_function_single_interrupt+0x34/0x36 > > [] call_function_single_interrupt+0x6f/0x80 > > [] ? mwait_idle+0x94/0xcd > > [] ? mwait_idle+0x8b/0xcd > > [] cpu_idle+0xbb/0x114 > > [] rest_init+0xc1/0xc8 > > [] ? csum_partial_copy_generic+0x16c/0x16c > > [] start_kernel+0x3d4/0x3e1 > > [] ? kernel_init+0x1f7/0x1f7 > > [] x86_64_start_reservations+0xb8/0xbd > > [] x86_64_start_kernel+0x101/0x110 > > This patch clears q->root_blkg and q->root_rl.blkg when root blkg > is destroyed. > __blk_queue_next_rl(), which uses q->root_blkg without check, > is changed to exit early when all blkg's are destroyed. > Thanks. This patch looks good to me. Acked-by: Vivek Goyal Vivek > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c > index f3b44a6..a31e678 100644 > --- a/block/blk-cgroup.c > +++ b/block/blk-cgroup.c > @@ -285,6 +285,13 @@ static void blkg_destroy_all(struct request_queue *q) > blkg_destroy(blkg); > spin_unlock(&blkcg->lock); > } > + > + /* > + * root blkg is destroyed. Just clear the pointer since > + * root_rl does not take reference on root blkg. > + */ > + q->root_blkg = NULL; > + q->root_rl.blkg = NULL; > } > > static void blkg_rcu_free(struct rcu_head *rcu_head) > @@ -326,6 +333,9 @@ struct request_list *__blk_queue_next_rl(struct request_list *rl, > */ > if (rl == &q->root_rl) { > ent = &q->blkg_list; > + /* There are no more block groups, hence no request lists */ > + if (list_empty(ent)) > + return NULL; > } else { > blkg = container_of(rl, struct blkcg_gq, rl); > ent = &blkg->q_node; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/