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



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