WARNING: proc registration bug in snmp6_register_dev

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: ab6f762f printk: queue wake_up_klogd irq_work only if per-..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1395613fe00000
kernel config: https://syzkaller.appspot.com/x/.config?x=3010ccb0f380f660
dashboard link: https://syzkaller.appspot.com/bug?extid=1d51c8b74efa4c44adeb
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

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+1d51c8...@syzkaller.appspotmail.com

------------[ cut here ]------------
proc_dir_entry 'dev_snmp6/hsr1' already registered
WARNING: CPU: 0 PID: 22141 at fs/proc/generic.c:363 proc_register+0x2bc/0x4e0 fs/proc/generic.c:362
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 22141 Comm: syz-executor.2 Not tainted 5.6.0-syzkaller #0
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+0x1e9/0x30e lib/dump_stack.c:118
panic+0x264/0x7a0 kernel/panic.c:221
__warn+0x209/0x210 kernel/panic.c:582
report_bug+0x1ac/0x2d0 lib/bug.c:195
fixup_bug arch/x86/kernel/traps.c:175 [inline]
do_error_trap+0xca/0x1c0 arch/x86/kernel/traps.c:267
do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
RIP: 0010:proc_register+0x2bc/0x4e0 fs/proc/generic.c:362
Code: 08 4c 8b 74 24 28 48 8b 6c 24 20 74 08 48 89 ef e8 99 29 d1 ff 48 8b 55 00 48 c7 c7 24 4e e9 88 48 89 de 31 c0 e8 e4 7c 65 ff <0f> 0b 48 c7 c7 20 e6 32 89 e8 66 41 2a 06 48 8b 44 24 30 42 8a 04
RSP: 0000:ffffc900088feec0 EFLAGS: 00010246
RAX: f20851673ab1bb00 RBX: ffff8880908a5264 RCX: 0000000000040000
RDX: ffffc9000df22000 RSI: 00000000000150b4 RDI: 00000000000150b5
RBP: ffff88808981bc18 R08: ffffffff815cac69 R09: ffffed1015d06660
R10: ffffed1015d06660 R11: 0000000000000000 R12: dffffc0000000000
R13: 0000000000000004 R14: ffff88808981bbd4 R15: ffff88808981bb40
proc_create_single_data+0x18e/0x1e0 fs/proc/generic.c:631
snmp6_register_dev+0xa1/0x110 net/ipv6/proc.c:254
ipv6_add_dev+0x509/0x1430 net/ipv6/addrconf.c:408
addrconf_notify+0x5f8/0x3ad0 net/ipv6/addrconf.c:3503
notifier_call_chain kernel/notifier.c:83 [inline]
__raw_notifier_call_chain kernel/notifier.c:361 [inline]
raw_notifier_call_chain+0xd4/0x170 kernel/notifier.c:368
call_netdevice_notifiers_info net/core/dev.c:1948 [inline]
call_netdevice_notifiers_extack net/core/dev.c:1960 [inline]
call_netdevice_notifiers net/core/dev.c:1974 [inline]
register_netdevice+0x14a4/0x1a50 net/core/dev.c:9421
hsr_dev_finalize+0x425/0x6d0 net/hsr/hsr_device.c:486
hsr_newlink+0x3b5/0x460 net/hsr/hsr_netlink.c:77
__rtnl_newlink net/core/rtnetlink.c:3333 [inline]
rtnl_newlink+0x143e/0x1c00 net/core/rtnetlink.c:3391
rtnetlink_rcv_msg+0x889/0xd40 net/core/rtnetlink.c:5454
netlink_rcv_skb+0x190/0x3a0 net/netlink/af_netlink.c:2469
netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
netlink_unicast+0x786/0x940 net/netlink/af_netlink.c:1329
netlink_sendmsg+0xa57/0xd70 net/netlink/af_netlink.c:1918
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg net/socket.c:672 [inline]
____sys_sendmsg+0x4f9/0x7c0 net/socket.c:2362
___sys_sendmsg net/socket.c:2416 [inline]
__sys_sendmsg+0x2a6/0x360 net/socket.c:2449
do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x45c889
Code: ad b6 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f007299ac78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f007299b6d4 RCX: 000000000045c889
RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000000000006
RBP: 000000000076c180 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000009fc R14: 00000000004ccb7c R15: 000000000076c18c
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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[Hillf Danton]

On Wed, 15 Apr 2020 02:20:14 -0700

Unregister netdev when it's the time to do so.

--- a/net/hsr/hsr_device.c
+++ b/net/hsr/hsr_device.c
@@ -361,6 +361,7 @@ static void hsr_dev_destroy(struct net_d
hsr = netdev_priv(hsr_dev);

hsr_debugfs_term(hsr);
+ unregister_netdev(hsr_dev);

list_for_each_entry_safe(port, tmp, &hsr->ports, port_list)
hsr_del_port(port);
@@ -485,18 +486,20 @@ int hsr_dev_finalize(struct net_device *

res = hsr_add_port(hsr, slave[0], HSR_PT_SLAVE_A);
if (res)
- goto fail;
+ goto unregister;
res = hsr_add_port(hsr, slave[1], HSR_PT_SLAVE_B);
if (res)
- goto fail;
+ goto unregister;

mod_timer(&hsr->prune_timer, jiffies + msecs_to_jiffies(PRUNE_PERIOD));
res = hsr_debugfs_init(hsr, hsr_dev);
if (res)
- goto fail;
+ goto unregister;

return 0;

+unregister:
+ unregister_netdev(hsr_dev);
fail:
list_for_each_entry_safe(port, tmp, &hsr->ports, port_list)
hsr_del_port(port);

[Taehee Yoo]

This is hsr module bug.
When a hsr interface is being removed,
"/proc/net/dev_snmp6/<interface name>" is removed and it is created again
because of NETDEV_CHANGEMTU after NETDEV_UNREGISTER.
So, this resource can't be released in the RTNL mutex critical section.
This remained resources will be released by netdev_run_todo() but it is
not protected by RTNL mutex. So that creating a new interface
routine(rtnl_newlink()) can be executed concurrently.
This routine would try to create the same proc entry
("/proc/net/dev_snmp6/<interface name>")
At this point, this warning could occur.
In order to fix this problem, ->dellink() can be used.
But the patch would cause conflict with 34a9c361dd48
("hsr: remove hsr interface if all slaves are removed").
That commit is not merged into "net" branch yet.
So, I will send fix patch after the merge.

Test commands:
#SHELL1
ip link add dummy0 type dummy
ip link add dummy1 type dummy
ip link set dummy0 mtu 1300
while :
do
ip link add hsr0 type hsr slave1 dummy0 slave2 dummy1
done
#SHELL2
while :
do
ip link del hsr0
done

Thank you,
Taehee Yoo

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: ac935d22 Add linux-next specific files for 20200415
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17006f4c100000
kernel config: https://syzkaller.appspot.com/x/.config?x=bc498783097e9019
dashboard link: https://syzkaller.appspot.com/bug?extid=1d51c8b74efa4c44adeb
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=148e6150100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=115c379c100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1d51c8...@syzkaller.appspotmail.com

------------[ cut here ]------------
proc_dir_entry 'dev_snmp6/hsr1' already registered

WARNING: CPU: 0 PID: 7289 at fs/proc/generic.c:362 proc_register+0x40b/0x580 fs/proc/generic.c:362

Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 7289 Comm: syz-executor779 Not tainted 5.7.0-rc1-next-20200415-syzkaller #0

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+0x188/0x20d lib/dump_stack.c:118
panic+0x2e3/0x75c kernel/panic.c:221
__warn.cold+0x2f/0x35 kernel/panic.c:582
report_bug+0x27b/0x2f0 lib/bug.c:195
fixup_bug arch/x86/kernel/traps.c:175 [inline]
fixup_bug arch/x86/kernel/traps.c:170 [inline]
do_error_trap+0x12b/0x220 arch/x86/kernel/traps.c:267

do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027

RIP: 0010:proc_register+0x40b/0x580 fs/proc/generic.c:362
Code: ff df 48 89 f9 48 c1 e9 03 80 3c 01 00 0f 85 5c 01 00 00 48 8b 04 24 48 c7 c7 a0 7a 39 88 48 8b b0 d8 00 00 00 e8 4d 2d 61 ff <0f> 0b 48 c7 c7 a0 ac ac 89 e8 f7 5b f3 05 48 8b 4c 24 28 48 b8 00
RSP: 0018:ffffc90005956cc8 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff8880a9138ac8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815ce211 RDI: fffff52000b2ad8b
RBP: ffff8880a1ab3a80 R08: ffff888087c40340 R09: ffffed1015cc66b1
R10: ffff8880ae633587 R11: ffffed1015cc66b0 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff8880a6561240 R15: 0000000000000004
proc_create_single_data+0xdb/0x130 fs/proc/generic.c:631
snmp6_register_dev+0xbe/0x140 net/ipv6/proc.c:254
ipv6_add_dev net/ipv6/addrconf.c:408 [inline]
ipv6_add_dev+0x54b/0x10b0 net/ipv6/addrconf.c:365
addrconf_notify+0x960/0x2310 net/ipv6/addrconf.c:3503
notifier_call_chain+0xc0/0x230 kernel/notifier.c:83
call_netdevice_notifiers_info net/core/dev.c:1948 [inline]
call_netdevice_notifiers_info+0xb5/0x130 net/core/dev.c:1933

call_netdevice_notifiers_extack net/core/dev.c:1960 [inline]
call_netdevice_notifiers net/core/dev.c:1974 [inline]

register_netdevice+0xd70/0x10b0 net/core/dev.c:9423
hsr_dev_finalize+0x516/0x746 net/hsr/hsr_device.c:486
hsr_newlink+0x27c/0x520 net/hsr/hsr_netlink.c:83
__rtnl_newlink+0xf18/0x1590 net/core/rtnetlink.c:3333
rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3391
rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5454
netlink_rcv_skb+0x15a/0x410 net/netlink/af_netlink.c:2469
netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
netlink_unicast+0x537/0x740 net/netlink/af_netlink.c:1329
netlink_sendmsg+0x882/0xe10 net/netlink/af_netlink.c:1918
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:672
____sys_sendmsg+0x6bf/0x7e0 net/socket.c:2362
___sys_sendmsg+0x100/0x170 net/socket.c:2416
__sys_sendmsg+0xec/0x1b0 net/socket.c:2449
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x449409
Code: e8 cc 14 03 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 9b 0c fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fa3c088fdb8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000006dfca8 RCX: 0000000000449409
RDX: 0000000000000000 RSI: 0000000020000040 RDI: 000000000000000e
RBP: 00000000006dfca0 R08: 0000000000000014 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 00000000006dfcac
R13: 00007ffc318e2f1f R14: 00007fa3c08909c0 R15: 00000000006dfcac

[syzbot]

syzbot has bisected this bug to:

commit e0a4b99773d3d8d3fb40087805f8fd858a23e582
Author: Taehee Yoo <ap42...@gmail.com>
Date: Fri Feb 28 18:02:10 2020 +0000

hsr: use upper/lower device infrastructure

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14811182100000
start commit: ac935d22 Add linux-next specific files for 20200415
git tree: linux-next
final crash: https://syzkaller.appspot.com/x/report.txt?x=16811182100000
console output: https://syzkaller.appspot.com/x/log.txt?x=12811182100000

kernel config: https://syzkaller.appspot.com/x/.config?x=bc498783097e9019
dashboard link: https://syzkaller.appspot.com/bug?extid=1d51c8b74efa4c44adeb

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=148e6150100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=115c379c100000

Reported-by: syzbot+1d51c8...@syzkaller.appspotmail.com
Fixes: e0a4b99773d3 ("hsr: use upper/lower device infrastructure")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection