From 319561669a59d8e9206ab311ae5433ef92fd79d1 Mon Sep 17 00:00:00 2001 From: Alistair Popple Date: Thu, 21 Apr 2022 16:36:10 -0700 Subject: [PATCH] mm/mmu_notifier.c: fix race in mmu_interval_notifier_remove() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Jason Gunthorpe Cc: Christian König Cc: John Hubbard Cc: Ralph Campbell Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mmu_notifier.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c index 459d195d2ff6..f45ff1b7626a 100644 --- a/mm/mmu_notifier.c +++ b/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 mmu_interval_notifier *interval_sub) 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);