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When an interface is being deleted, "/proc/net/dev_snmp6/<interface name>"
is deleted.
The function for this is addrconf_ifdown() in the addrconf_notify() and
it is called by notification, which is NETDEV_UNREGISTER.
But, if NETDEV_CHANGEMTU is triggered after NETDEV_UNREGISTER,
this proc file will be created again.
This recreated proc file will be deleted by netdev_wati_allrefs().
Before netdev_wait_allrefs() is called, creating a new HSR interface
routine can be executed and It tries to create a proc file but it will
find an un-deleted proc file.
At this point, it warns about it.
To avoid this situation, it can use ->dellink() instead of
->ndo_uninit() to release resources because ->dellink() is called
before NETDEV_UNREGISTER.
So, a proc file will not be recreated.
Test commands
ip link add dummy0 type dummy
ip link add dummy1 type dummy
ip link set dummy0 mtu 1300
#SHELL1
while :
do
ip link add hsr0 type hsr slave1 dummy0 slave2 dummy1
done
#SHELL2
while :
do
ip link del hsr0
done
Splat looks like:
[ 9888.980852][ T2752] proc_dir_entry 'dev_snmp6/hsr0' already registered
[ 9888.981797][ C2] WARNING: CPU: 2 PID: 2752 at fs/proc/generic.c:372 proc_register+0x2d5/0x430
[ 9888.981798][ C2] Modules linked in: hsr dummy veth openvswitch nsh nf_conncount nf_nat nf_conntrack nf_defrag_ipv6x
[ 9888.981814][ C2] CPU: 2 PID: 2752 Comm: ip Tainted: G W 5.8.0-rc1+ #616
[ 9888.981815][ C2] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[ 9888.981816][ C2] RIP: 0010:proc_register+0x2d5/0x430
[ 9888.981818][ C2] Code: fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 65 01 00 00 49 8b b5 e0 00 00 00 48 89 ea 40
[ 9888.981819][ C2] RSP: 0018:ffff8880628dedf0 EFLAGS: 00010286
[ 9888.981821][ C2] RAX: dffffc0000000008 RBX: ffff888028c69170 RCX: ffffffffaae09a62
[ 9888.981822][ C2] RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff88806c9f75ac
[ 9888.981823][ C2] RBP: ffff888028c693f4 R08: ffffed100d9401bd R09: ffffed100d9401bd
[ 9888.981824][ C2] R10: ffffffffaddf406f R11: 0000000000000001 R12: ffff888028c69308
[ 9888.981825][ C2] R13: ffff8880663584c8 R14: dffffc0000000000 R15: ffffed100518d27e
[ 9888.981827][ C2] FS: 00007f3876b3b0c0(0000) GS:ffff88806c800000(0000) knlGS:0000000000000000
[ 9888.981828][ C2] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 9888.981829][ C2] CR2: 00007f387601a8c0 CR3: 000000004101a002 CR4: 00000000000606e0
[ 9888.981830][ C2] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 9888.981831][ C2] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 9888.981832][ C2] Call Trace:
[ 9888.981833][ C2] ? snmp6_seq_show+0x180/0x180
[ 9888.981834][ C2] proc_create_single_data+0x7c/0xa0
[ 9888.981835][ C2] snmp6_register_dev+0xb0/0x130
[ 9888.981836][ C2] ipv6_add_dev+0x4b7/0xf60
[ 9888.981837][ C2] addrconf_notify+0x684/0x1ca0
[ 9888.981838][ C2] ? __mutex_unlock_slowpath+0xd0/0x670
[ 9888.981839][ C2] ? kasan_unpoison_shadow+0x30/0x40
[ 9888.981840][ C2] ? wait_for_completion+0x250/0x250
[ 9888.981841][ C2] ? inet6_ifinfo_notify+0x100/0x100
[ 9888.981842][ C2] ? dropmon_net_event+0x227/0x410
[ 9888.981843][ C2] ? notifier_call_chain+0x90/0x160
[ 9888.981844][ C2] ? inet6_ifinfo_notify+0x100/0x100
[ 9888.981845][ C2] notifier_call_chain+0x90/0x160
[ 9888.981846][ C2] register_netdevice+0xbe5/0x1070
[ ... ]
Reported-by: syzbot+1d51c8b74efa4c44adeb@syzkaller.appspotmail.com
Fixes: e0a4b99773 ("hsr: use upper/lower device infrastructure")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
de0083c7ed