[PATCH 4.14 24/82] netfilter: ctnetlink: suspicious RCU usage in ctnetlink_dump_helpinfo

Greg Kroah-Hartman
2021-07-26T15:57:05Z

From: Vasily Averin <vvs@virtuozzo.com>

commit c23a9fd209bc6f8c1fa6ee303fdf037d784a1627 upstream.

Two patches listed below removed ctnetlink_dump_helpinfo call from under
rcu_read_lock. Now its rcu_dereference generates following warning:
=============================
WARNING: suspicious RCU usage
5.13.0+ #5 Not tainted
-----------------------------
net/netfilter/nf_conntrack_netlink.c:221 suspicious rcu_dereference_check() usage!

other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
stack backtrace:
CPU: 1 PID: 2251 Comm: conntrack Not tainted 5.13.0+ #5
Call Trace:
dump_stack+0x7f/0xa1
ctnetlink_dump_helpinfo+0x134/0x150 [nf_conntrack_netlink]
ctnetlink_fill_info+0x2c2/0x390 [nf_conntrack_netlink]
ctnetlink_dump_table+0x13f/0x370 [nf_conntrack_netlink]
netlink_dump+0x10c/0x370
__netlink_dump_start+0x1a7/0x260
ctnetlink_get_conntrack+0x1e5/0x250 [nf_conntrack_netlink]
nfnetlink_rcv_msg+0x613/0x993 [nfnetlink]
netlink_rcv_skb+0x50/0x100
nfnetlink_rcv+0x55/0x120 [nfnetlink]
netlink_unicast+0x181/0x260
netlink_sendmsg+0x23f/0x460
sock_sendmsg+0x5b/0x60
__sys_sendto+0xf1/0x160
__x64_sys_sendto+0x24/0x30
do_syscall_64+0x36/0x70
entry_SYSCALL_64_after_hwframe+0x44/0xae

Fixes: 49ca022bccc5 ("netfilter: ctnetlink: don't dump ct extensions of unconfirmed conntracks")
Fixes: 0b35f6031a00 ("netfilter: Remove duplicated rcu_read_lock.")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/netfilter/nf_conntrack_netlink.c | 3 +++
1 file changed, 3 insertions(+)

--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -196,6 +196,7 @@ static int ctnetlink_dump_helpinfo(struc
if (!help)
return 0;

+ rcu_read_lock();
helper = rcu_dereference(help->helper);
if (!helper)
goto out;
@@ -211,9 +212,11 @@ static int ctnetlink_dump_helpinfo(struc

nla_nest_end(skb, nest_helper);
out:
+ rcu_read_unlock();
return 0;

nla_put_failure:
+ rcu_read_unlock();
return -1;
}