Re: [PATCH] netlink: Deal with ESRCH error in nlmsg_notify()

From: Yonghong Song <yhs@fb.com>
To: Yajun Deng <yajun.deng@linux.dev>, <davem@davemloft.net>,
	<kuba@kernel.org>, <ast@kernel.org>, <andrii@kernel.org>,
	<kafai@fb.com>, <songliubraving@fb.com>,
	<john.fastabend@gmail.com>, <kpsingh@kernel.org>
Cc: <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] netlink: Deal with ESRCH error in nlmsg_notify()
Date: Mon, 19 Jul 2021 07:47:15 -0700	[thread overview]
Message-ID: <0ada4233-6c9d-82f5-f33f-55805bfbe37d@fb.com> (raw)
In-Reply-To: <20210719051816.11762-1-yajun.deng@linux.dev>

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@fb.com>
> Signed-off-by: Yajun Deng <yajun.deng@linux.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);

1 net/core/rtnetlink.c      rtnl_notify     734 nlmsg_notify(rtnl, skb, 
pid, group, report, flags);

2 net/netfilter/nfnetlink.c nfnetlink_send  176 return 
nlmsg_notify(nfnlnet->nfnl, skb, portid, group, echo, flags);

3 net/netlink/genetlink.c   genl_notify    1506 nlmsg_notify(sk, skb, 
info->snd_portid, group, report, flags);

> ---
>   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;
>   	}
>   
> 