Subject: Re: general protection fault in fib6_purge_rt

From: syzbot <[email-masked]>
Date: Tue, 12 Mar 2019 11:49:04 -0700

syzbot has found a reproducer for the following crash on:

HEAD commit:    cf08baa2 Add linux-next specific files for 20190306
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12f6755f200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c8b6073d992e8217
dashboard link: https://syzkaller.appspot.com/bug?extid=a25307ad099309f1c2b9
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: amd64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16b2c56f200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13b8890b200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]

Started in network mode
Own node identity ac1414aa, cluster identity 4711
New replicast peer: 172.20.20.187
Enabled bearer <udp:syz1>, priority 10
Enabling of bearer <udp:syz1> rejected, already enabled
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 7821 Comm: syz-executor772 Not tainted 5.0.0-next-20190306 #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:fib6_drop_pcpu_from net/ipv6/ip6_fib.c:924 [inline]
RIP: 0010:fib6_purge_rt+0x4b3/0x670 net/ipv6/ip6_fib.c:960
Code: 0f b6 35 5a f6 44 03 31 ff 44 89 f6 e8 a6 1c 5b fb 45 84 f6 0f 84 b3  
00 00 00 e8 58 1b 5b fb 49 8d 7f 70 48 89 f8 48 c1 e8 03 <80> 3c 18 00 0f  
85 64 01 00 00 48 89 f8 4d 8b 77 70 48 c1 e8 03 80
RSP: 0018:ffff8880a5a26e98 EFLAGS: 00010202
RAX: 000000000000000e RBX: dffffc0000000000 RCX: ffffffff861579a9
RDX: 0000000000000000 RSI: ffffffff861578d8 RDI: 0000000000000071
RBP: ffff8880a5a26ef0 R08: ffff88808f9a6300 R09: ffffed101406c2f6
R10: ffffed101406c2f5 R11: ffff8880a03617af R12: 0000000000000000
R13: ffff8880a0361780 R14: 0000000000000001 R15: 0000000000000001
FS:  00007fe8383f8700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005612a363f110 CR3: 0000000093362000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  fib6_del_route net/ipv6/ip6_fib.c:1813 [inline]
  fib6_del+0xac2/0x10a0 net/ipv6/ip6_fib.c:1844
  fib6_clean_node+0x3a8/0x590 net/ipv6/ip6_fib.c:2006
  fib6_walk_continue+0x495/0x900 net/ipv6/ip6_fib.c:1928
  fib6_walk+0x9d/0x100 net/ipv6/ip6_fib.c:1976
  fib6_clean_tree+0xe0/0x120 net/ipv6/ip6_fib.c:2055
  __fib6_clean_all+0x118/0x2a0 net/ipv6/ip6_fib.c:2071
  fib6_clean_all+0x2b/0x40 net/ipv6/ip6_fib.c:2082
  rt6_sync_down_dev+0x134/0x150 net/ipv6/route.c:4051
  rt6_disable_ip+0x27/0x5f0 net/ipv6/route.c:4056
  addrconf_ifdown+0xa2/0x1220 net/ipv6/addrconf.c:3705
  addrconf_notify+0x19a/0x2260 net/ipv6/addrconf.c:3630
  notifier_call_chain+0xc7/0x240 kernel/notifier.c:93
  __raw_notifier_call_chain kernel/notifier.c:394 [inline]
  raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:401
  call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1739
  call_netdevice_notifiers_extack net/core/dev.c:1751 [inline]
  call_netdevice_notifiers net/core/dev.c:1765 [inline]
  dev_close_many+0x33f/0x6f0 net/core/dev.c:1508
  rollback_registered_many+0x43b/0xfd0 net/core/dev.c:8161
  rollback_registered+0x109/0x1d0 net/core/dev.c:8226
  unregister_netdevice_queue net/core/dev.c:9273 [inline]
  unregister_netdevice_queue+0x1ee/0x2c0 net/core/dev.c:9266
  unregister_netdevice include/linux/netdevice.h:2655 [inline]
  __tun_detach+0xd5b/0x1000 drivers/net/tun.c:727
  tun_detach drivers/net/tun.c:744 [inline]
  tun_chr_close+0xe0/0x180 drivers/net/tun.c:3435
  __fput+0x2e5/0x8d0 fs/file_table.c:278
  ____fput+0x16/0x20 fs/file_table.c:309
  task_work_run+0x14a/0x1c0 kernel/task_work.c:113
  exit_task_work include/linux/task_work.h:22 [inline]
  do_exit+0x90a/0x2fa0 kernel/exit.c:876
  do_group_exit+0x135/0x370 kernel/exit.c:980
  get_signal+0x399/0x1d50 kernel/signal.c:2577
  do_signal+0x87/0x1940 arch/x86/kernel/signal.c:816
  exit_to_usermode_loop+0x244/0x2c0 arch/x86/entry/common.c:162
  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
  do_syscall_64+0x52d/0x610 arch/x86/entry/common.c:293
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x44bca9
Code: 5b 65 73 63 61 70 65 20 63 6f 6e 74 72 6f 6c 2d 63 68 61 72 61 63 74  
65 72 73 5d 20 00 5b 64 72 6f 70 20 63 6f 6e 74 72 6f 6c <2d> 63 68 61 72  
61 63 74 65 72 73 5d 20 00 5b 73 6c 61 73 68 65 73
RSP: 002b:00007fe8383f7cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00000000006dec48 RCX: 000000000044bca9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00000000006dec48
RBP: 00000000006dec40 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dec4c
R13: 00007ffd4d27000f R14: 00007fe8383f89c0 R15: 000000000000002d
Modules linked in:
---[ end trace 9a88786341e68810 ]---
RIP: 0010:fib6_drop_pcpu_from net/ipv6/ip6_fib.c:924 [inline]
RIP: 0010:fib6_purge_rt+0x4b3/0x670 net/ipv6/ip6_fib.c:960
Code: 0f b6 35 5a f6 44 03 31 ff 44 89 f6 e8 a6 1c 5b fb 45 84 f6 0f 84 b3  
00 00 00 e8 58 1b 5b fb 49 8d 7f 70 48 89 f8 48 c1 e8 03 <80> 3c 18 00 0f  
85 64 01 00 00 48 89 f8 4d 8b 77 70 48 c1 e8 03 80
RSP: 0018:ffff8880a5a26e98 EFLAGS: 00010202
RAX: 000000000000000e RBX: dffffc0000000000 RCX: ffffffff861579a9
RDX: 0000000000000000 RSI: ffffffff861578d8 RDI: 0000000000000071
RBP: ffff8880a5a26ef0 R08: ffff88808f9a6300 R09: ffffed101406c2f6
R10: ffffed101406c2f5 R11: ffff8880a03617af R12: 0000000000000000
R13: ffff8880a0361780 R14: 0000000000000001 R15: 0000000000000001
FS:  00007fe8383f8700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005612a363f110 CR3: 0000000093362000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400