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

Kirill Tkhai ktkhai at virtuozzo.com
Thu Apr 13 03:09:12 PDT 2017


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,



More information about the Devel mailing list