[Devel] [PATCH] sched/numa: Fix use-after-free bug in the task_numa_compare

Kirill Tkhai ktkhai at virtuozzo.com
Thu Apr 13 04:00:03 PDT 2017


On 13.04.2017 13:58, Konstantin Khorenko wrote:
> May be apply following patch as well?
> It mostly reverts your patch back.

It has a patch-dependence, so I didn't choose it. Which way you prefer?
 
> commit bac7857319bcf7fed329a10bb760053e761115c0
> Author: Oleg Nesterov <oleg at redhat.com>
> Date:   Wed May 18 21:57:33 2016 +0200
> 
>     sched/fair: Use task_rcu_dereference()
> 
> -- 
> Best regards,
> 
> Konstantin Khorenko,
> Virtuozzo Linux Kernel Team
> 
> On 04/13/2017 01:09 PM, Kirill Tkhai wrote:
>> ms commit 1dff76b92f69 by Gavin Guo <gavin.guo at canonical.com>
>>
>> The following message can be observed on the Ubuntu v3.13.0-65 with KASan
>> backported:
>>
>>   ==================================================================
>>   BUG: KASan: use after free in task_numa_find_cpu+0x64c/0x890 at addr ffff880dd393ecd8
>>   Read of size 8 by task qemu-system-x86/3998900
>>   =============================================================================
>>   BUG kmalloc-128 (Tainted: G    B        ): kasan: bad access detected
>>   -----------------------------------------------------------------------------
>>
>>   INFO: Allocated in task_numa_fault+0xc1b/0xed0 age=41980 cpu=18 pid=3998890
>>         __slab_alloc+0x4f8/0x560
>>         __kmalloc+0x1eb/0x280
>>         task_numa_fault+0xc1b/0xed0
>>         do_numa_page+0x192/0x200
>>         handle_mm_fault+0x808/0x1160
>>         __do_page_fault+0x218/0x750
>>         do_page_fault+0x1a/0x70
>>         page_fault+0x28/0x30
>>         SyS_poll+0x66/0x1a0
>>         system_call_fastpath+0x1a/0x1f
>>   INFO: Freed in task_numa_free+0x1d2/0x200 age=62 cpu=18 pid=0
>>         __slab_free+0x2ab/0x3f0
>>         kfree+0x161/0x170
>>         task_numa_free+0x1d2/0x200
>>         finish_task_switch+0x1d2/0x210
>>         __schedule+0x5d4/0xc60
>>         schedule_preempt_disabled+0x40/0xc0
>>         cpu_startup_entry+0x2da/0x340
>>         start_secondary+0x28f/0x360
>>   Call Trace:
>>    [<ffffffff81a6ce35>] dump_stack+0x45/0x56
>>    [<ffffffff81244aed>] print_trailer+0xfd/0x170
>>    [<ffffffff8124ac36>] object_err+0x36/0x40
>>    [<ffffffff8124cbf9>] kasan_report_error+0x1e9/0x3a0
>>    [<ffffffff8124d260>] kasan_report+0x40/0x50
>>    [<ffffffff810dda7c>] ? task_numa_find_cpu+0x64c/0x890
>>    [<ffffffff8124bee9>] __asan_load8+0x69/0xa0
>>    [<ffffffff814f5c38>] ? find_next_bit+0xd8/0x120
>>    [<ffffffff810dda7c>] task_numa_find_cpu+0x64c/0x890
>>    [<ffffffff810de16c>] task_numa_migrate+0x4ac/0x7b0
>>    [<ffffffff810de523>] numa_migrate_preferred+0xb3/0xc0
>>    [<ffffffff810e0b88>] task_numa_fault+0xb88/0xed0
>>    [<ffffffff8120ef02>] do_numa_page+0x192/0x200
>>    [<ffffffff81211038>] handle_mm_fault+0x808/0x1160
>>    [<ffffffff810d7dbd>] ? sched_clock_cpu+0x10d/0x160
>>    [<ffffffff81068c52>] ? native_load_tls+0x82/0xa0
>>    [<ffffffff81a7bd68>] __do_page_fault+0x218/0x750
>>    [<ffffffff810c2186>] ? hrtimer_try_to_cancel+0x76/0x160
>>    [<ffffffff81a6f5e7>] ? schedule_hrtimeout_range_clock.part.24+0xf7/0x1c0
>>    [<ffffffff81a7c2ba>] do_page_fault+0x1a/0x70
>>    [<ffffffff81a772e8>] page_fault+0x28/0x30
>>    [<ffffffff8128cbd4>] ? do_sys_poll+0x1c4/0x6d0
>>    [<ffffffff810e64f6>] ? enqueue_task_fair+0x4b6/0xaa0
>>    [<ffffffff810233c9>] ? sched_clock+0x9/0x10
>>    [<ffffffff810cf70a>] ? resched_task+0x7a/0xc0
>>    [<ffffffff810d0663>] ? check_preempt_curr+0xb3/0x130
>>    [<ffffffff8128b5c0>] ? poll_select_copy_remaining+0x170/0x170
>>    [<ffffffff810d3bc0>] ? wake_up_state+0x10/0x20
>>    [<ffffffff8112a28f>] ? drop_futex_key_refs.isra.14+0x1f/0x90
>>    [<ffffffff8112d40e>] ? futex_requeue+0x3de/0xba0
>>    [<ffffffff8112e49e>] ? do_futex+0xbe/0x8f0
>>    [<ffffffff81022c89>] ? read_tsc+0x9/0x20
>>    [<ffffffff8111bd9d>] ? ktime_get_ts+0x12d/0x170
>>    [<ffffffff8108f699>] ? timespec_add_safe+0x59/0xe0
>>    [<ffffffff8128d1f6>] SyS_poll+0x66/0x1a0
>>    [<ffffffff81a830dd>] system_call_fastpath+0x1a/0x1f
>>
>> As commit 1effd9f19324 ("sched/numa: Fix unsafe get_task_struct() in
>> task_numa_assign()") points out, the rcu_read_lock() cannot protect the
>> task_struct from being freed in the finish_task_switch(). And the bug
>> happens in the process of calculation of imp which requires the access of
>> p->numa_faults being freed in the following path:
>>
>> do_exit()
>>         current->flags |= PF_EXITING;
>>     release_task()
>>         ~~delayed_put_task_struct()~~
>>     schedule()
>>     ...
>>     ...
>> rq->curr = next;
>>     context_switch()
>>         finish_task_switch()
>>             put_task_struct()
>>                 __put_task_struct()
>>                     task_numa_free()
>>
>> The fix here to get_task_struct() early before end of dst_rq->lock to
>> protect the calculation process and also put_task_struct() in the
>> corresponding point if finally the dst_rq->curr somehow cannot be
>> assigned.
>>
>> Additional credit to Liang Chen who helped fix the error logic and add the
>> put_task_struct() to the place it missed.
>>
>> Signed-off-by: Gavin Guo <gavin.guo at canonical.com>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
>> Cc: Andrea Arcangeli <aarcange at redhat.com>
>> Cc: Andrew Morton <akpm at linux-foundation.org>
>> Cc: Hugh Dickins <hughd at google.com>
>> Cc: Linus Torvalds <torvalds at linux-foundation.org>
>> Cc: Mel Gorman <mgorman at suse.de>
>> Cc: Peter Zijlstra <peterz at infradead.org>
>> Cc: Rik van Riel <riel at redhat.com>
>> Cc: Thomas Gleixner <tglx at linutronix.de>
>> Cc: jay.vosburgh at canonical.com
>> Cc: liang.chen at canonical.com
>> Link: http://lkml.kernel.org/r/1453264618-17645-1-git-send-email-gavin.guo@canonical.com
>> Signed-off-by: Ingo Molnar <mingo at kernel.org>
>>
>> In scope of https://jira.sw.ru/browse/PSBM-62208
>>
>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>> ---
>>  kernel/sched/fair.c |   29 ++++++++++++++++++++++-------
>>  1 file changed, 22 insertions(+), 7 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index daf709e40b6..4fde0d42a95 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -1388,8 +1388,6 @@ static void task_numa_assign(struct task_numa_env *env,
>>  {
>>      if (env->best_task)
>>          put_task_struct(env->best_task);
>> -    if (p)
>> -        get_task_struct(p);
>>
>>      env->best_task = p;
>>      env->best_imp = imp;
>> @@ -1411,19 +1409,29 @@ static void task_numa_compare(struct task_numa_env *env,
>>      long dst_load, src_load;
>>      long load;
>>      long imp = (groupimp > 0) ? groupimp : taskimp;
>> +    bool assigned = false;
>>
>>      rcu_read_lock();
>>      raw_spin_lock_irq(&dst_rq->lock);
>>      cur = dst_rq->curr;
>>      /*
>> -     * No need to move the exiting task, and this ensures that ->curr
>> -     * wasn't reaped and thus get_task_struct() in task_numa_assign()
>> -     * is safe under RCU read lock.
>> -     * Note that rcu_read_lock() itself can't protect from the final
>> -     * put_task_struct() after the last schedule().
>> +     * No need to move the exiting task or idle task.
>>       */
>>      if ((cur->flags & PF_EXITING) || is_idle_task(cur))
>>          cur = NULL;
>> +    else {
>> +        /*
>> +         * The task_struct must be protected here to protect the
>> +         * p->numa_faults access in the task_weight since the
>> +         * numa_faults could already be freed in the following path:
>> +         * finish_task_switch()
>> +         *     --> put_task_struct()
>> +         *         --> __put_task_struct()
>> +         *             --> task_numa_free()
>> +         */
>> +        get_task_struct(cur);
>> +    }
>> +
>>      raw_spin_unlock_irq(&dst_rq->lock);
>>
>>      /*
>> @@ -1513,9 +1521,16 @@ static void task_numa_compare(struct task_numa_env *env,
>>          goto unlock;
>>
>>  assign:
>> +    assigned = true;
>>      task_numa_assign(env, cur, imp);
>>  unlock:
>>      rcu_read_unlock();
>> +    /*
>> +     * The dst_rq->curr isn't assigned. The protection for task_struct is
>> +     * finished.
>> +     */
>> +    if (cur && !assigned)
>> +        put_task_struct(cur);
>>  }
>>
>>  static void task_numa_find_cpu(struct task_numa_env *env,
>>
>> .
>>


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