[PATCH 5.15 082/124] mm/mmu_notifier.c: fix race in mmu_interval_notifier_remove()

From: Greg Kroah-Hartman
Date: Tue Apr 26 2022 - 05:17:44 EST

From: Alistair Popple <apopple@xxxxxxxxxx>

commit 319561669a59d8e9206ab311ae5433ef92fd79d1 upstream.

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()
----------------------------------- ------------------------------------
seq = subscriptions->invalidate_seq;
spin_lock(subscriptions->lock); spin_unlock(subscriptions->lock);
wait_event(invalidate_seq != seq);
interval_tree_remove(interval_sub); kfree(interval_sub);

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>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
mm/mmu_notifier.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -1036,6 +1036,18 @@ int 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
if (seq)
- READ_ONCE(subscriptions->invalidate_seq) != seq);
+ mmu_interval_seq_released(subscriptions, seq));

/* pairs with mmgrab in mmu_interval_notifier_insert() */