From 65635cbc37e011e71b208257a25e7c1078cd039b Mon Sep 17 00:00:00 2001 From: Jun'ichi Nomura Date: Wed, 17 Oct 2012 17:45:36 +0900 Subject: 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(+) (limited to 'block/blk-cgroup.c') 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) -- cgit v1.2.3 From 65c77fd9e8a1c8c3da0bbbea6b7efa3d6ef265f8 Mon Sep 17 00:00:00 2001 From: Jun'ichi Nomura Date: Mon, 22 Oct 2012 10:15:37 +0900 Subject: blkcg: stop iteration early if root_rl is the only request list __blk_queue_next_rl() finds next request list based on blkg_list while skipping root_blkg in the list. OTOH, root_rl is special as it may exist even without root_blkg. Though the later part of the function handles such a case correctly, exiting early is good for readability of the code. Signed-off-by: Jun'ichi Nomura Cc: Tejun Heo Acked-by: Vivek Goyal Signed-off-by: Jens Axboe --- block/blk-cgroup.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'block/blk-cgroup.c') diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 3ad5e3fbf579..d0b770391ad4 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -333,6 +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; -- cgit v1.2.3