linux-kernel - Re: [PATCH] netlink: Deal with ESRCH error in nlmsg

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Date:   Tue, 20 Jul 2021 02:47:01 +0000
From:   yajun.deng@...ux.dev
To:     "Yonghong Song" <yhs@...com>, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, andrii@...nel.org, kafai@...com,
        songliubraving@...com, john.fastabend@...il.com, kpsingh@...nel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netlink: Deal with ESRCH error in nlmsg_notify()

July 19, 2021 10:47 PM, "Yonghong Song" <yhs@...com> wrote:

> On 7/18/21 10:18 PM, Yajun Deng wrote:
> 
>> Yonghong Song report:
>> The bpf selftest tc_bpf failed with latest bpf-next.
>> The following is the command to run and the result:
>> $ ./test_progs -n 132
>> [ 40.947571] bpf_testmod: loading out-of-tree module taints kernel.
>> test_tc_bpf:PASS:test_tc_bpf__open_and_load 0 nsec
>> test_tc_bpf:PASS:bpf_tc_hook_create(BPF_TC_INGRESS) 0 nsec
>> test_tc_bpf:PASS:bpf_tc_hook_create invalid hook.attach_point 0 nsec
>> test_tc_bpf_basic:PASS:bpf_obj_get_info_by_fd 0 nsec
>> test_tc_bpf_basic:PASS:bpf_tc_attach 0 nsec
>> test_tc_bpf_basic:PASS:handle set 0 nsec
>> test_tc_bpf_basic:PASS:priority set 0 nsec
>> test_tc_bpf_basic:PASS:prog_id set 0 nsec
>> test_tc_bpf_basic:PASS:bpf_tc_attach replace mode 0 nsec
>> test_tc_bpf_basic:PASS:bpf_tc_query 0 nsec
>> test_tc_bpf_basic:PASS:handle set 0 nsec
>> test_tc_bpf_basic:PASS:priority set 0 nsec
>> test_tc_bpf_basic:PASS:prog_id set 0 nsec
>> libbpf: Kernel error message: Failed to send filter delete notification
>> test_tc_bpf_basic:FAIL:bpf_tc_detach unexpected error: -3 (errno 3)
>> test_tc_bpf:FAIL:test_tc_internal ingress unexpected error: -3 (errno 3)
>> The failure seems due to the commit
>> cfdf0d9ae75b ("rtnetlink: use nlmsg_notify() in rtnetlink_send()")
>> Deal with ESRCH error in nlmsg_notify() even the report variable is zero.
>> Reported-by: Yonghong Song <yhs@...com>
>> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> 
> Thanks for quick fix. This does fix the bpf selftest issu.
> But does this change have negative impacts on other
> nlmsg_notify() callers, below 1-3 items?
> 
> 0 net/core/rtnetlink.c rtnetlink_send 714 return nlmsg_notify(rtnl, skb, pid, group, echo,
> GFP_KERNEL);

This is exactly what we need.
> 
> 1 net/core/rtnetlink.c rtnl_notify 734 nlmsg_notify(rtnl, skb, pid, group, report, flags);
> 
It doesn't matter because there is no return value.
 
> 2 net/netfilter/nfnetlink.c nfnetlink_send 176 return nlmsg_notify(nfnlnet->nfnl, skb, portid,
> group, echo, flags);
> 
It only ctnetlink_conntrack_event() use the return value when call nfnetlink_send() in
net/netfilter/nf_conntrack_netlink.c, but it doesn't matter when the return value is ESRCH or zero.

> 3 net/netlink/genetlink.c genl_notify 1506 nlmsg_notify(sk, skb, info->snd_portid, group, report,
> flags);
> 
It doesn't matter because there is no return value.

I think the caller for nlmsg_notify() doesn't need deal with the ESRCH. It also deal with ESRCH
when report variable is not zero.

>> ---
>> net/netlink/af_netlink.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
>> index 380f95aacdec..24b7cf447bc5 100644
>> --- a/net/netlink/af_netlink.c
>> +++ b/net/netlink/af_netlink.c
>> @@ -2545,13 +2545,15 @@ int nlmsg_notify(struct sock *sk, struct sk_buff *skb, u32 portid,
>> /* errors reported via destination sk->sk_err, but propagate
>> * delivery errors if NETLINK_BROADCAST_ERROR flag is set */
>> err = nlmsg_multicast(sk, skb, exclude_portid, group, flags);
>> + if (err == -ESRCH)
>> + err = 0;
>> }
>>> if (report) {
>> int err2;
>>> err2 = nlmsg_unicast(sk, skb, portid);
>> - if (!err || err == -ESRCH)
>> + if (!err)
>> err = err2;
>> }
>>>