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From:   Lorenzo Stoakes <lstoakes@gmail.com>
Date:   Wed, 11 Nov 2020 19:26:47 +0000
Message-ID: <CAA5enKY8mBicpc7kZKKLG5LeVFhVJtRQ73MYVFM0Az2bbiGv8g@mail.gmail.com>
Subject: Re: linux-next boot error: BUG: unable to handle kernel NULL pointer
 dereference in mempool_init_node
To:     Andrey Konovalov <andreyknvl@google.com>
Cc:     Qian Cai <cai@redhat.com>,
        syzbot <syzbot+2d6f3dad1a42d86a5801@syzkaller.appspotmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Linux-Next Mailing List <linux-next@vger.kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>
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On Wed, 11 Nov 2020 at 17:44, Andrey Konovalov <andreyknvl@google.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