linux-kernel - Re: linux-next boot error: BUG: unable to handle kernel NULL pointer dereference in mempool_init

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Date:   Wed, 11 Nov 2020 19:26:47 +0000
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Qian Cai <cai@...hat.com>,
        syzbot <syzbot+2d6f3dad1a42d86a5801@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>
Subject: Re: linux-next boot error: BUG: unable to handle kernel NULL pointer
 dereference in mempool_init_node

On Wed, 11 Nov 2020 at 17:44, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> I'll try to reproduce this and figure out the issue. Thanks for letting us know!

I hope you don't mind me diving in here, I was taking a look just now
and managed to reproduce this locally - I bisected the issue to
105397399 ("kasan: simplify kasan_poison_kfree").

If I stick a simple check in as below it fixes the issue, so I'm
guessing something is violating the assumptions in 105397399?


diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 7a94cebc0324..16163159a017 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -387,6 +387,11 @@ void __kasan_slab_free_mempool(void *ptr, unsigned long ip)
        struct page *page;

        page = virt_to_head_page(ptr);
+
+       if (!PageSlab(page)) {
+               return;
+       }
+
        ____kasan_slab_free(page->slab_cache, ptr, ip, false);
 }


--
Lorenzo Stoakes
https://ljs.io