Re: [PATCH] blkcg: Fix use-after-free of q->root_blkg and q->root_rl.blkg

[Jens Axboe <axboe@kernel.dk>]

On 2012-10-17 10:45, Jun'ichi Nomura wrote:
> 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.

Thanks, applied to for-linus (and marked stable).

-- 
Jens Axboe