[Devel,RHEL7,COMMIT] sched/numa: Fix use-after-free bug in the task_numa_compare

Submitted by Konstantin Khorenko on April 14, 2017, 4:13 p.m.

Details

Message ID 201704141613.v3EGDoMG021169@finist_cl7.x64_64.work.ct
State New
Series "sched/numa: Fix use-after-free bug in the task_numa_compare"
Headers show

Commit Message

Konstantin Khorenko April 14, 2017, 4:13 p.m.
The commit is pushed to "branch-rh7-3.10.0-514.10.2.vz7.29.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.10.2.vz7.29.16
------>
commit 6288cc7ab5d0e2ee16295cfaba182ba0d29ed497
Author: Gavin Guo <gavin.guo@canonical.com>
Date:   Fri Apr 14 20:13:49 2017 +0400

    sched/numa: Fix use-after-free bug in the task_numa_compare
    
    ms commit 1dff76b92f69 by Gavin Guo <gavin.guo@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@canonical.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: jay.vosburgh@canonical.com
    Cc: liang.chen@canonical.com
    Link: http://lkml.kernel.org/r/1453264618-17645-1-git-send-email-gavin.guo@canonical.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    
    In scope of https://jira.sw.ru/browse/PSBM-62208
    
    Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 kernel/sched/fair.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

Patch hide | download patch | download mbox

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index daf709e..4fde0d4 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 @@  balance:
 		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,