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Date:   Sun, 26 May 2019 08:43:03 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+83c135be90fc92db7e13@...kaller.appspotmail.com>,
        bpf <bpf@...r.kernel.org>, kasan-dev <kasan-dev@...glegroups.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: KASAN: use-after-free Read in class_equal

On Sat, May 25, 2019 at 7:38 PM syzbot
<syzbot+83c135be90fc92db7e13@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    c50bbf61 Merge tag 'platform-drivers-x86-v5.2-2' of git://..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12130c9aa00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fc045131472947d7
> dashboard link: https://syzkaller.appspot.com/bug?extid=83c135be90fc92db7e13
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12e7d84ca00000

>From the repro looks like

#syz dup: KASAN: slab-out-of-bounds Read in class_equal

+bpf mailing list

If bpf maps started badly smashing memory in a way that KASAN can't
detect, please fix asap. Or we will start getting dozens of random
reports. The usual question: why does not KASAN detect the root cause
smash? How can we make it detect it?


> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+83c135be90fc92db7e13@...kaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in class_equal+0x40/0x50
> kernel/locking/lockdep.c:1527
> Read of size 8 at addr ffff88807aedf360 by task syz-executor.0/9275
>
> CPU: 0 PID: 9275 Comm: syz-executor.0 Not tainted 5.2.0-rc1+ #7
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>
> Allocated by task 9264:
>   save_stack+0x23/0x90 mm/kasan/common.c:71
>   set_track mm/kasan/common.c:79 [inline]
>   __kasan_kmalloc mm/kasan/common.c:489 [inline]
>   __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
>   kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:497
>   slab_post_alloc_hook mm/slab.h:437 [inline]
>   slab_alloc mm/slab.c:3326 [inline]
>   kmem_cache_alloc+0x11a/0x6f0 mm/slab.c:3488
>   getname_flags fs/namei.c:138 [inline]
>   getname_flags+0xd6/0x5b0 fs/namei.c:128
>   getname+0x1a/0x20 fs/namei.c:209
>   do_sys_open+0x2c9/0x5d0 fs/open.c:1064
>   __do_sys_open fs/open.c:1088 [inline]
>   __se_sys_open fs/open.c:1083 [inline]
>   __x64_sys_open+0x7e/0xc0 fs/open.c:1083
>   do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 9264:
>   save_stack+0x23/0x90 mm/kasan/common.c:71
>   set_track mm/kasan/common.c:79 [inline]
>   __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
>   kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
>   __cache_free mm/slab.c:3432 [inline]
>   kmem_cache_free+0x86/0x260 mm/slab.c:3698
>   putname+0xef/0x130 fs/namei.c:259
>   do_sys_open+0x318/0x5d0 fs/open.c:1079
>   __do_sys_open fs/open.c:1088 [inline]
>   __se_sys_open fs/open.c:1083 [inline]
>   __x64_sys_open+0x7e/0xc0 fs/open.c:1083
>   do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff88807aede580
>   which belongs to the cache names_cache of size 4096
> The buggy address is located 3552 bytes inside of
>   4096-byte region [ffff88807aede580, ffff88807aedf580)
> The buggy address belongs to the page:
> page:ffffea0001ebb780 refcount:1 mapcount:0 mapping:ffff8880aa596c40
> index:0x0 compound_mapcount: 0
> flags: 0x1fffc0000010200(slab|head)
> raw: 01fffc0000010200 ffffea0001ebb708 ffffea0001ebb908 ffff8880aa596c40
> raw: 0000000000000000 ffff88807aede580 0000000100000001 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>   ffff88807aedf200: 00 00 fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff88807aedf280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb f1 f1
> > ffff88807aedf300: f1 f1 00 f2 f2 f2 00 f2 f2 f2 fb fb fb fb 00 00
>                                                         ^
>   ffff88807aedf380: 00 f3 f3 f3 f3 f3 fb fb fb fb fb fb fb fb fb fb
>   ffff88807aedf400: fb fb fb fb fb fb fb fb fb fb fb fb fb 00 00 00
> ==================================================================
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
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