WARNING: suspicious RCU usage in ovs_flow_tbl_masks_cache_size

WARNING: suspicious RCU usage in ovs_flow_tbl_masks_cache_size

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    2f631133 net: Pass NULL to skb_network_protocol() when we ..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12c1f770900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=91a13b78c7dc258d
dashboard link: https://syzkaller.appspot.com/bug?extid=f612c02823acb02ff9bc
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10e8430a900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=123549fc900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f612c02823acb02ff9bc@syzkaller.appspotmail.com

netlink: 'syz-executor210': attribute type 2 has an invalid length.
device \x04 entered promiscuous mode
=============================
WARNING: suspicious RCU usage
5.8.0-rc7-syzkaller #0 Not tainted
-----------------------------
net/openvswitch/flow_table.c:940 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
2 locks held by syz-executor210/6812:
 #0: ffffffff8a8319b0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40 net/netlink/genetlink.c:741
 #1: ffffffff8aa786a8 (ovs_mutex){+.+.}-{3:3}, at: ovs_lock net/openvswitch/datapath.c:105 [inline]
 #1: ffffffff8aa786a8 (ovs_mutex){+.+.}-{3:3}, at: ovs_dp_cmd_new+0x4db/0xea0 net/openvswitch/datapath.c:1707

stack backtrace:
CPU: 0 PID: 6812 Comm: syz-executor210 Not tainted 5.8.0-rc7-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+0x18f/0x20d lib/dump_stack.c:118
 ovs_flow_tbl_masks_cache_size+0xc3/0xe0 net/openvswitch/flow_table.c:940
 ovs_dp_cmd_fill_info+0x4e4/0x880 net/openvswitch/datapath.c:1539
 ovs_dp_cmd_new+0x584/0xea0 net/openvswitch/datapath.c:1728
 genl_family_rcv_msg_doit net/netlink/genetlink.c:669 [inline]
 genl_family_rcv_msg net/netlink/genetlink.c:714 [inline]
 genl_rcv_msg+0x61d/0x980 net/netlink/genetlink.c:731
 netlink_rcv_skb+0x15a/0x430 net/netlink/af_netlink.c:2470
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:742
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:671
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2359
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2413
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2446
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4402d9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 7b 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffd71bb22a8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004402d9
RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000


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Re: WARNING: suspicious RCU usage in ovs_flow_tbl_masks_cache_size

[syzbot]

syzbot has bisected this issue to:

commit 9bf24f594c6acf676fb8c229f152c21bfb915ddb
Author: Eelco Chaudron <echaudro@redhat.com>
Date:   Fri Jul 31 12:21:34 2020 +0000

    net: openvswitch: make masks cache size configurable

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=110e06dc900000
start commit:   2f631133 net: Pass NULL to skb_network_protocol() when we ..
git tree:       net-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=130e06dc900000
console output: https://syzkaller.appspot.com/x/log.txt?x=150e06dc900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=91a13b78c7dc258d
dashboard link: https://syzkaller.appspot.com/bug?extid=f612c02823acb02ff9bc
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10e8430a900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=123549fc900000

Reported-by: syzbot+f612c02823acb02ff9bc@syzkaller.appspotmail.com
Fixes: 9bf24f594c6a ("net: openvswitch: make masks cache size configurable")

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