linux-kernel - Re: BUG: corrupted list in cpu_stop_queue

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Date:   Mon, 9 Jul 2018 21:55:17 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     syzbot <syzbot+d8a8e42dfba0454286ff@...kaller.appspotmail.com>,
        bigeasy@...utronix.de, linux-kernel@...r.kernel.org,
        matt@...eblueprint.co.uk, mingo@...nel.org, peterz@...radead.org,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
        linux-mm <linux-mm@...ck.org>
Subject: Re: BUG: corrupted list in cpu_stop_queue_work

Hello Matthew,

It seems to me that there are other locations which do not check xas_store()
failure. Is that really OK? If they are OK, I think we want a comment like
/* This never fails. */ or /* Failure is OK because ... */
for each call without failure check.



>From d6f24d6eecd79836502527624f8086f4e3e4c331 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Mon, 9 Jul 2018 15:58:44 +0900
Subject: [PATCH] shmem: Fix crash upon xas_store() failure.

syzbot is reporting list corruption [1]. This is because xas_store() from
shmem_add_to_page_cache() is not handling memory allocation failure. Fix
this by checking xas_error() after xas_store().

[1] https://syzkaller.appspot.com/bug?id=ccf34b892706ff6f3321da526329476eab23d5a0

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Reported-by: syzbot+d8a8e42dfba0454286ff@...kaller.appspotmail.com
Fixes: "shmem: Convert shmem_add_to_page_cache to XArray"
---
 mm/shmem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/shmem.c b/mm/shmem.c
index 0f151c8..382aeb3 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -606,6 +606,8 @@ static int shmem_add_to_page_cache(struct page *page,
 		}
 next:
 		xas_store(&xas, page + i);
+		if (xas_error(&xas))
+			goto unlock;
 		if (++i < nr) {
 			xas_next(&xas);
 			goto next;
-- 
1.8.3.1