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Date:   Mon, 28 Dec 2020 16:00:18 +0800
From:   Walter Wu <walter-zh.wu@...iatek.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     <kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        <linux-mediatek@...ts.infradead.org>,
        Walter Wu <walter-zh.wu@...iatek.com>
Subject: [PATCH] kasan: fix null pointer dereference in kasan_record_aux_stack

Syzbot reported the following [1]:

 BUG: kernel NULL pointer dereference, address: 0000000000000008
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 2d993067 P4D 2d993067 PUD 19a3c067 PMD 0
 Oops: 0000 [#1] PREEMPT SMP KASAN
 CPU: 1 PID: 3852 Comm: kworker/1:2 Not tainted 5.10.0-syzkaller #0
 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 Workqueue: events free_ipc
 RIP: 0010:kasan_record_aux_stack+0x77/0xb0

Add null checking slab object from kasan_get_alloc_meta()
in order to avoid null pointer dereference.

[1] https://syzkaller.appspot.com/x/log.txt?x=10a82a50d00000

Signed-off-by: Walter Wu <walter-zh.wu@...iatek.com>
Suggested-by: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
CC: Dmitry Vyukov <dvyukov@...gle.com>
CC: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Alexander Potapenko <glider@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
 mm/kasan/generic.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 1dd5a0f99372..5106b84b07d4 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -337,6 +337,8 @@ void kasan_record_aux_stack(void *addr)
 	cache = page->slab_cache;
 	object = nearest_obj(cache, page, addr);
 	alloc_meta = kasan_get_alloc_meta(cache, object);
+	if (!alloc_meta)
+		return;
 
 	alloc_meta->aux_stack[1] = alloc_meta->aux_stack[0];
 	alloc_meta->aux_stack[0] = kasan_save_stack(GFP_NOWAIT);
-- 
2.18.0

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