Messages in this thread | | | Date | Thu, 11 Oct 2012 14:55:36 -0400 | From | Vivek Goyal <> | Subject | Re: [PATCH] Fix use-after-free of q->root_blkg and q->root_rl.blkg |
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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: > > <IRQ> [<ffffffff810453bd>] warn_slowpath_common+0x85/0x9d > > [<ffffffff810453ef>] warn_slowpath_null+0x1a/0x1c > > [<ffffffff811d5f8d>] blk_put_rl+0x4d/0x95 > > [<ffffffff811d614a>] __blk_put_request+0xc3/0xcb > > [<ffffffff811d71a3>] blk_finish_request+0x232/0x23f > > [<ffffffff811d76c3>] ? blk_end_bidi_request+0x34/0x5d > > [<ffffffff811d76d1>] blk_end_bidi_request+0x42/0x5d > > [<ffffffff811d7728>] blk_end_request+0x10/0x12 > > [<ffffffff812cdf16>] scsi_io_completion+0x207/0x4d5 > > [<ffffffff812c6fcf>] scsi_finish_command+0xfa/0x103 > > [<ffffffff812ce2f8>] scsi_softirq_done+0xff/0x108 > > [<ffffffff811dcea5>] blk_done_softirq+0x8d/0xa1 > > [<ffffffff810915d5>] ? generic_smp_call_function_single_interrupt+0x9f/0xd7 > > [<ffffffff8104cf5b>] __do_softirq+0x102/0x213 > > [<ffffffff8108a5ec>] ? lock_release_holdtime+0xb6/0xbb > > [<ffffffff8104d2b4>] ? raise_softirq_irqoff+0x9/0x3d > > [<ffffffff81424dfc>] call_softirq+0x1c/0x30 > > [<ffffffff81011beb>] do_softirq+0x4b/0xa3 > > [<ffffffff8104cdb0>] irq_exit+0x53/0xd5 > > [<ffffffff8102d865>] smp_call_function_single_interrupt+0x34/0x36 > > [<ffffffff8142486f>] call_function_single_interrupt+0x6f/0x80 > > <EOI> [<ffffffff8101800b>] ? mwait_idle+0x94/0xcd > > [<ffffffff81018002>] ? mwait_idle+0x8b/0xcd > > [<ffffffff81017811>] cpu_idle+0xbb/0x114 > > [<ffffffff81401fbd>] rest_init+0xc1/0xc8 > > [<ffffffff81401efc>] ? csum_partial_copy_generic+0x16c/0x16c > > [<ffffffff81cdbd3d>] start_kernel+0x3d4/0x3e1 > > [<ffffffff81cdb79e>] ? kernel_init+0x1f7/0x1f7 > > [<ffffffff81cdb2dd>] x86_64_start_reservations+0xb8/0xbd > > [<ffffffff81cdb3e3>] 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 <vgoyal@redhat.com>
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;
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