From 0d845d504d68ed6e60bc353cccedc4facedd56c3 Mon Sep 17 00:00:00 2001
From: liqiong <liqiong@nfschina.com>
Date: Sat, 7 May 2022 08:24:36 +0000
Subject: [PATCH] mm: fix dereference a null pointer in
 migrate[_huge]_page_move_mapping()

stable inclusion
from linux-4.19.236
commit deebce9df9ffaa62613bfcd8351d0c43a9a66108
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5646A
CVE: NA

--------------------------------

Upstream doesn't use radix tree any more in migrate.c, no need this patch.

The two functions look up a slot and dereference the pointer,
If the pointer is null, the kernel would crash and dump.

The 'numad' service calls 'migrate_pages' periodically. If some slots
being replaced (Cache Eviction), the radix_tree_lookup_slot() returns
a null pointer that causes kernel crash.

"numad":  crash> bt
[exception RIP: migrate_page_move_mapping+337]

Introduce pointer checking to avoid dereference a null pointer.

Cc: <stable@vger.kernel.org> # linux-4.19.y
Signed-off-by: liqiong <liqiong@nfschina.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>
---
 mm/migrate.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index ecfa8829acfd..3a20900e19e0 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -473,6 +473,10 @@ int migrate_page_move_mapping(struct address_space *mapping,
 
 	pslot = radix_tree_lookup_slot(&mapping->i_pages,
  					page_index(page));
+	if (pslot == NULL) {
+		xa_unlock_irq(&mapping->i_pages);
+		return -EAGAIN;
+	}
 
 	expected_count += hpage_nr_pages(page) + page_has_private(page);
 	if (page_count(page) != expected_count ||
@@ -596,6 +600,10 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 	xa_lock_irq(&mapping->i_pages);
 
 	pslot = radix_tree_lookup_slot(&mapping->i_pages, page_index(page));
+	if (pslot == NULL) {
+		xa_unlock_irq(&mapping->i_pages);
+		return -EAGAIN;
+	}
 
 	expected_count = 2 + page_has_private(page);
 	if (page_count(page) != expected_count ||
-- 
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