From 65635cbc37e011e71b208257a25e7c1078cd039b Mon Sep 17 00:00:00 2001 From: Jun'ichi Nomura Date: Wed, 17 Oct 2012 17:45:36 +0900 Subject: [PATCH] blkcg: Fix use-after-free of q->root_blkg and q->root_rl.blkg 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. Signed-off-by: Jun'ichi Nomura Acked-by: Vivek Goyal Acked-by: Tejun Heo Cc: stable@kernel.org Signed-off-by: Jens Axboe --- block/blk-cgroup.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index cafcd7431189..3ad5e3fbf579 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)