netdev - Re: [PATCH iproute2] ip: do not exit if RTM

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Date:   Tue, 22 Sep 2020 08:28:37 +0200 (CEST)
From:   Jan Engelhardt <jengelh@...i.de>
To:     Stephen Hemminger <stephen@...workplumber.org>
cc:     netdev@...r.kernel.org
Subject: Re: [PATCH iproute2] ip: do not exit if RTM_GETNSID failed


On Tuesday 2020-09-22 02:22, Stephen Hemminger wrote:
>Jan Engelhardt <jengelh@...i.de> wrote:
>
>> `ip addr` when run under qemu-user-riscv64, fails. This likely is
>> due to qemu-5.1 not doing translation of RTM_GETNSID calls.
>> 
>> 2: host0@if5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
>>     link/ether 5a:44:da:1a:c4:0b brd ff:ff:ff:ff:ff:ff
>> request send failed: Operation not supported
>> 
>> Treat the situation similar to an absence of procfs.
>> 
>> Signed-off-by: Jan Engelhardt <jengelh@...i.de>
>
>Not a good idea to hide a platform bug in ip command.
>When you do this, you risk creating all sorts of issues for people that
>run ip commands in container environments where the send is rejected (perhaps by SELinux)
>and then things go off into a different failure.

In the very same function you do

  fd = open("/proc/self/ns/net", O_RDONLY);

which equally hides a potential platform bug (namely, forgetting to
mount /proc in a chroot, or in case SELinux was improperly set-up).
Why is this measured two different ways?


>From 4222d059c910136f5e2b5c6de96ddaf06828c1d5 Mon Sep 17 00:00:00 2001
From: Jan Engelhardt <jengelh@...i.de>
Date: Tue, 22 Sep 2020 01:41:50 +0200
Subject: [PATCH] ip: add error reporting when RTM_GETNSID failed

`ip addr` when run under qemu-user-riscv64, fails. This likely is
due to qemu-5.1 not doing translation of RTM_GETNSID calls. Aborting
ip completely is the wrong response however. This patch reworks the
error handling.

2: host0@if5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 5a:44:da:1a:c4:0b brd ff:ff:ff:ff:ff:ff
request send failed: Operation not supported

Signed-off-by: Jan Engelhardt <jengelh@...i.de>
---
 ip/ipnetns.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index 46cc235b..e7a45653 100644
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -78,6 +78,8 @@ static int ipnetns_have_nsid(void)
 	if (have_rtnl_getnsid < 0) {
 		fd = open("/proc/self/ns/net", O_RDONLY);
 		if (fd < 0) {
+			fprintf(stderr, "/proc/self/ns/net: %s. "
+				"Continuing anyway.\n", strerror(errno));
 			have_rtnl_getnsid = 0;
 			return 0;
 		}
@@ -85,8 +87,11 @@ static int ipnetns_have_nsid(void)
 		addattr32(&req.n, 1024, NETNSA_FD, fd);
 
 		if (rtnl_send(&rth, &req.n, req.n.nlmsg_len) < 0) {
-			perror("request send failed");
-			exit(1);
+			fprintf(stderr, "rtnl_send(RTM_GETNSID): %s. "
+				"Continuing anyway.\n", strerror(errno));
+			have_rtnl_getnsid = 0;
+			close(fd);
+			return 0;
 		}
 		rtnl_listen(&rth, ipnetns_accept_msg, NULL);
 		close(fd);
-- 
2.28.0