@@ -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);
The patch titled Subject: mm/mmu_notifier.c: fix race in mmu_interval_notifier_remove() has been removed from the -mm tree. Its filename was mm-mmu_notifierc-fix-race-in-mmu_interval_notifier_remove.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Alistair Popple <apopple@nvidia.com> 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@nvidia.com Fixes: 99cb252f5e68 ("mm/mmu_notifier: add an interval tree notifier") Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Cc: Christian König <christian.koenig@amd.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Ralph Campbell <rcampbell@nvidia.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- mm/mmu_notifier.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)