Message-ID: <d39c169e-9201-7e0d-44e7-ad775b185115@gmail.com>
Date:   Thu, 6 Sep 2018 12:53:14 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     syzbot <syzbot+579adfa56843da894bc5@...kaller.appspotmail.com>,
        ast@...nel.org, daniel@...earbox.net, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in bpf_tcp_close (2)

On 09/06/2018 01:22 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    11f026b4e306 libbpf: Remove the duplicate checking of func..
> git tree:       bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=153c55ca400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4c7e83258d6e0156
> dashboard link: https://syzkaller.appspot.com/bug?extid=579adfa56843da894bc5
> 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+579adfa56843da894bc5@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
> BUG: KASAN: use-after-free in virt_spin_lock arch/x86/include/asm/qspinlock.h:65 [inline]
> BUG: KASAN: use-after-free in native_queued_spin_lock_slowpath+0x189/0x1220 kernel/locking/qspinlock.c:305
> Read of size 4 at addr ffff8801bfd651a0 by task syz-executor1/9753
> 
> CPU: 1 PID: 9753 Comm: syz-executor1 Not tainted 4.19.0-rc2+ #89
> 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+0x1c9/0x2b4 lib/dump_stack.c:113
>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
>  check_memory_region_inline mm/kasan/kasan.c:260 [inline]
>  check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
>  kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272
>  atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
>  virt_spin_lock arch/x86/include/asm/qspinlock.h:65 [inline]
>  native_queued_spin_lock_slowpath+0x189/0x1220 kernel/locking/qspinlock.c:305
>  pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:679 [inline]
>  queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:32 [inline]
>  queued_spin_lock include/asm-generic/qspinlock.h:88 [inline]
>  do_raw_spin_lock+0x1a7/0x200 kernel/locking/spinlock_debug.c:113
>  __raw_spin_lock_bh include/linux/spinlock_api_smp.h:136 [inline]
>  _raw_spin_lock_bh+0x39/0x40 kernel/locking/spinlock.c:168
>  bpf_tcp_close+0x68e/0x10d0 kernel/bpf/sockmap.c:349
>  inet_release+0x104/0x1f0 net/ipv4/af_inet.c:428
>  inet6_release+0x50/0x70 net/ipv6/af_inet6.c:457
>  __sock_release+0xd7/0x250 net/socket.c:579
>  sock_close+0x19/0x20 net/socket.c:1139
>  __fput+0x38a/0xa40 fs/file_table.c:278
>  ____fput+0x15/0x20 fs/file_table.c:309
>  task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
>  tracehook_notify_resume include/linux/tracehook.h:193 [inline]
>  exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
>  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>  do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x410c51
> Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 34 19 00 00 c3 48 83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
> RSP: 002b:00007ffeacb37d60 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 0000000000000008 RCX: 0000000000410c51
> RDX: 0000000000000000 RSI: 0000000000731f70 RDI: 0000000000000007
> RBP: 0000000000000000 R08: ffffffffffffffff R09: ffffffffffffffff
> R10: 00007ffeacb37c90 R11: 0000000000000293 R12: 0000000000000010
> R13: 0000000000022aa9 R14: 000000000000004d R15: badc0ffeebadface
> 
> Allocated by task 9754:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
>  kmem_cache_alloc_trace+0x152/0x730 mm/slab.c:3620
>  kmalloc include/linux/slab.h:513 [inline]
>  kzalloc include/linux/slab.h:707 [inline]
>  sock_map_alloc+0x209/0x430 kernel/bpf/sockmap.c:1653
>  find_and_alloc_map kernel/bpf/syscall.c:129 [inline]
>  map_create+0x3bd/0x1100 kernel/bpf/syscall.c:509
>  __do_sys_bpf kernel/bpf/syscall.c:2356 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:2333 [inline]
>  __x64_sys_bpf+0x303/0x510 kernel/bpf/syscall.c:2333
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 13:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>  __cache_free mm/slab.c:3498 [inline]
>  kfree+0xd9/0x210 mm/slab.c:3813
>  sock_map_remove_complete kernel/bpf/sockmap.c:1561 [inline]
>  sock_map_free+0x428/0x570 kernel/bpf/sockmap.c:1756
>  bpf_map_free_deferred+0xba/0xf0 kernel/bpf/syscall.c:290
>  process_one_work+0xc73/0x1aa0 kernel/workqueue.c:2153
>  worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
>  kthread+0x35a/0x420 kernel/kthread.c:246
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:413
> 
> The buggy address belongs to the object at ffff8801bfd65080
>  which belongs to the cache kmalloc-512 of size 512
> The buggy address is located 288 bytes inside of
>  512-byte region [ffff8801bfd65080, ffff8801bfd65280)
> The buggy address belongs to the page:
> page:ffffea0006ff5940 count:1 mapcount:0 mapping:ffff8801dac00940 index:0xffff8801bfd65300
> flags: 0x2fffc0000000100(slab)
> raw: 02fffc0000000100 ffffea000702a488 ffffea00075c4148 ffff8801dac00940
> raw: ffff8801bfd65300 ffff8801bfd65080 0000000100000001 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8801bfd65080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801bfd65100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff8801bfd65180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                ^
>  ffff8801bfd65200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801bfd65280: fc fc fc fc fc fc fc fc 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.

Introduced here (by a new reference to the map from the
tcp close context where a parallel free'ing of the map which
does not have a RCU grace period before free),

commit 585f5a6252ee43ec8feeee07387e3fcc7e8bb292
Author: Daniel Borkmann <daniel@...earbox.net>
Date:   Thu Aug 16 21:49:10 2018 +0200

    bpf, sockmap: fix sock_map_ctx_update_elem race with exist/noexist

I'll have a fix shortly.

Thanks,
John

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