Date:   Fri, 28 Sep 2018 16:55:14 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+376cea2b0ef340db3dd4@...kaller.appspotmail.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-unionfs@...r.kernel.org
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: slab-out-of-bounds Read in string (2)

On Fri, Sep 28, 2018 at 4:45 PM, syzbot
<syzbot+376cea2b0ef340db3dd4@...kaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    c127e59bee3e Merge tag 'for_v4.19-rc6' of git://git.kernel..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13b2f32a400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=dfb440e26f0a6f6f
> dashboard link: https://syzkaller.appspot.com/bug?extid=376cea2b0ef340db3dd4
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+376cea2b0ef340db3dd4@...kaller.appspotmail.com

I guess this is overlayfs rather than printk. +overlayfs maintainers
In future syzbot will avoid attributing crashes to printk, because I
think it's not the first time crashes are mis-attributed to printk:
https://github.com/google/syzkaller/commit/41e4b32952f4590341ae872db0abf819b4004713


> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000140
> RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f0e714a76d4
> R13: 00000000004c32cb R14: 00000000004d4ef0 R15: 0000000000000004
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in string+0x298/0x2d0 lib/vsprintf.c:604
> Read of size 1 at addr ffff8801c36c66ba by task syz-executor2/27811
>
> CPU: 0 PID: 27811 Comm: syz-executor2 Not tainted 4.19.0-rc5+ #36
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
>  print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
>  __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
>  string+0x298/0x2d0 lib/vsprintf.c:604
>  vsnprintf+0x48e/0x1b60 lib/vsprintf.c:2293
>  vscnprintf+0x2d/0x80 lib/vsprintf.c:2396
>  vprintk_store+0x43/0x510 kernel/printk/printk.c:1847
>  vprintk_emit+0x1c1/0x930 kernel/printk/printk.c:1905
>  vprintk_default+0x28/0x30 kernel/printk/printk.c:1963
>  vprintk_func+0x7e/0x181 kernel/printk/printk_safe.c:398
>  printk+0xa7/0xcf kernel/printk/printk.c:1996
>  ovl_lookup_index.cold.15+0xe8/0x1f8 fs/overlayfs/namei.c:689
>  ovl_lookup+0x9f2/0x29c0 fs/overlayfs/namei.c:1022
>  __lookup_hash+0x12e/0x190 fs/namei.c:1546
>  do_rmdir+0x3b3/0x630 fs/namei.c:3930
>  __do_sys_rmdir fs/namei.c:3959 [inline]
>  __se_sys_rmdir fs/namei.c:3957 [inline]
>  __x64_sys_rmdir+0x36/0x40 fs/namei.c:3957
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x457579
> Code: 1d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff
> 0f 83 eb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f0e714a6c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
> RAX: ffffffffffffffda RBX: 00007f0e714a6c90 RCX: 0000000000457579
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000140
> RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f0e714a76d4
> R13: 00000000004c32cb R14: 00000000004d4ef0 R15: 0000000000000004
>
> Allocated by task 27811:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
>  __do_kmalloc mm/slab.c:3718 [inline]
>  __kmalloc+0x14e/0x760 mm/slab.c:3727
>  kmalloc_array include/linux/slab.h:635 [inline]
>  kcalloc include/linux/slab.h:646 [inline]
>  ovl_get_index_name_fh+0x57/0x180 fs/overlayfs/namei.c:596
>  ovl_get_index_name+0x5c/0x80 fs/overlayfs/namei.c:631
>  ovl_lookup_index+0xe4/0x700 fs/overlayfs/namei.c:678
>  ovl_lookup+0x9f2/0x29c0 fs/overlayfs/namei.c:1022
>  __lookup_hash+0x12e/0x190 fs/namei.c:1546
>  do_rmdir+0x3b3/0x630 fs/namei.c:3930
>  __do_sys_rmdir fs/namei.c:3959 [inline]
>  __se_sys_rmdir fs/namei.c:3957 [inline]
>  __x64_sys_rmdir+0x36/0x40 fs/namei.c:3957
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 5441:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>  __cache_free mm/slab.c:3498 [inline]
>  kfree+0xcf/0x230 mm/slab.c:3813
>  __vunmap+0x335/0x460 mm/vmalloc.c:1532
>  vfree+0x68/0x100 mm/vmalloc.c:1593
>  copy_entries_to_user net/ipv4/netfilter/ip_tables.c:870 [inline]
>  get_entries net/ipv4/netfilter/ip_tables.c:1027 [inline]
>  do_ipt_get_ctl+0x9eb/0xbc0 net/ipv4/netfilter/ip_tables.c:1703
>  nf_sockopt net/netfilter/nf_sockopt.c:104 [inline]
>  nf_getsockopt+0x80/0xe0 net/netfilter/nf_sockopt.c:122
>  ip_getsockopt+0x1af/0x240 net/ipv4/ip_sockglue.c:1577
>  tcp_getsockopt+0x93/0xe0 net/ipv4/tcp.c:3583
>  sock_common_getsockopt+0x9a/0xe0 net/core/sock.c:2997
>  __sys_getsockopt+0x1ad/0x390 net/socket.c:1939
>  __do_sys_getsockopt net/socket.c:1950 [inline]
>  __se_sys_getsockopt net/socket.c:1947 [inline]
>  __x64_sys_getsockopt+0xbe/0x150 net/socket.c:1947
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff8801c36c6680
>  which belongs to the cache kmalloc-64 of size 64
> The buggy address is located 58 bytes inside of
>  64-byte region [ffff8801c36c6680, ffff8801c36c66c0)
> The buggy address belongs to the page:
> page:ffffea00070db180 count:1 mapcount:0 mapping:ffff8801da800340
> index:0xffff8801c36c6380
> flags: 0x2fffc0000000100(slab)
> raw: 02fffc0000000100 ffffea0006d16508 ffffea000638a588 ffff8801da800340
> raw: ffff8801c36c6380 ffff8801c36c6000 000000010000001b 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff8801c36c6580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff8801c36c6600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>>
>> ffff8801c36c6680: 00 00 00 00 00 00 00 02 fc fc fc fc fc fc fc fc
>
>                                         ^
>  ffff8801c36c6700: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>  ffff8801c36c6780: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
> 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#bug-status-tracking for how to communicate with
> syzbot.
>
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