From: Alistair Popple <apopple@xxxxxxxxxx>
Subject: mm/mmu_notifier.c: fix race in mmu_interval_notifier_remove()
In some cases it is possible for mmu_interval_notifier_remove() to race
with mn_tree_inv_end() allowing it to return while the notifier data
structure is still in use. Consider the following sequence:
CPU0 - mn_tree_inv_end() CPU1 - mmu_interval_notifier_remove()
----------------------------------- ------------------------------------
spin_lock(subscriptions->lock);
seq = subscriptions->invalidate_seq;
spin_lock(subscriptions->lock); spin_unlock(subscriptions->lock);
subscriptions->invalidate_seq++;
wait_event(invalidate_seq != seq);
return;
interval_tree_remove(interval_sub); kfree(interval_sub);
spin_unlock(subscriptions->lock);
wake_up_all();
As the wait_event() condition is true it will return immediately. This
can lead to use-after-free type errors if the caller frees the data
structure containing the interval notifier subscription while it is still
on a deferred list. Fix this by taking the appropriate lock when reading
invalidate_seq to ensure proper synchronisation.
I observed this whilst running stress testing during some development.
You do have to be pretty unlucky, but it leads to the usual problems of
use-after-free (memory corruption, kernel crash, difficult to diagnose
WARN_ON, etc).
Link: https://lkml.kernel.org/r/20220420043734.476348-1-apopple@xxxxxxxxxx
Fixes: 99cb252f5e68 ("mm/mmu_notifier: add an interval tree notifier")
Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmu_notifier.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
--- a/mm/mmu_notifier.c~mm-mmu_notifierc-fix-race-in-mmu_interval_notifier_remove
+++ a/mm/mmu_notifier.c
@@ -1036,6 +1036,18 @@ int mmu_interval_notifier_insert_locked(
}
EXPORT_SYMBOL_GPL(mmu_interval_notifier_insert_locked);
+static bool
+mmu_interval_seq_released(struct mmu_notifier_subscriptions *subscriptions,
+ unsigned long seq)
+{
+ bool ret;
+
+ spin_lock(&subscriptions->lock);
+ ret = subscriptions->invalidate_seq != seq;
+ spin_unlock(&subscriptions->lock);
+ return ret;
+}
+
/**
* mmu_interval_notifier_remove - Remove a interval notifier
* @interval_sub: Interval subscription to unregister
@@ -1083,7 +1095,7 @@ void mmu_interval_notifier_remove(struct
lock_map_release(&__mmu_notifier_invalidate_range_start_map);
if (seq)
wait_event(subscriptions->wq,
- READ_ONCE(subscriptions->invalidate_seq) != seq);
+ mmu_interval_seq_released(subscriptions, seq));
/* pairs with mmgrab in mmu_interval_notifier_insert() */
mmdrop(mm);
_
