2021-07-01 05:06:38

by Vasily Averin

Subject: [PATCH NETFILTER v2] netfilter: nfnetlink: suspicious RCU usage in ctnetlink_dump_helpinfo

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 <[email protected]>
Reviewed-by: Florian Westphal <[email protected]>
---
v2: resent, original message was graylisted

net/netfilter/nf_conntrack_netlink.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 8690fc07030f..f3e8e6ce82c4 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -218,6 +218,7 @@ static int ctnetlink_dump_helpinfo(struct sk_buff *skb,
if (!help)
return 0;

+ rcu_read_lock();
helper = rcu_dereference(help->helper);
if (!helper)
goto out;
@@ -233,9 +234,11 @@ static int ctnetlink_dump_helpinfo(struct sk_buff *skb,

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

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

--
2.25.1

2021-07-02 00:55:55

by Pablo Neira Ayuso

Subject: Re: [PATCH NETFILTER v2] netfilter: nfnetlink: suspicious RCU usage in ctnetlink_dump_helpinfo

On Thu, Jul 01, 2021 at 08:02:49AM +0300, Vasily Averin wrote:
> 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!

Applied.