Patch "mm: fix dereference a null pointer in migrate[_huge]_page_move_mapping()" has been added to the 4.19-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    mm: fix dereference a null pointer in migrate[_huge]_page_move_mapping()

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-fix-dereference-a-null-pointer-in-migrate_page_move_mapping.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From liqiong@nfschina.com  Thu Mar 17 11:25:02 2022
From: liqiong <liqiong@nfschina.com>
Date: Thu, 17 Feb 2022 19:54:16 +0800
Subject: mm: fix dereference a null pointer in migrate[_huge]_page_move_mapping()
To: david@redhat.com, gregkh@linuxfoundation.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, liqiong <liqiong@nfschina.com>, stable@vger.kernel.org
Message-ID: <20220217115416.55835-1-liqiong@nfschina.com>

From: liqiong <liqiong@nfschina.com>

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>
---
 mm/migrate.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -472,6 +472,10 @@ int migrate_page_move_mapping(struct add
 
 	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 ||
@@ -590,6 +594,10 @@ int migrate_huge_page_move_mapping(struc
 	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 ||


Patches currently in stable-queue which might be from liqiong@nfschina.com are

queue-4.19/mm-fix-dereference-a-null-pointer-in-migrate_page_move_mapping.patch