netdev - [PATCH ipsec] xfrm: lwtunnel: squelch kernel warning in case XFRM encap type is not available

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Date:   Tue, 11 Oct 2022 11:01:37 +0300
From:   Eyal Birger <eyal.birger@...il.com>
To:     idosch@...sch.org, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, steffen.klassert@...unet.com,
        herbert@...dor.apana.org.au, dsahern@...nel.org,
        contact@...elbtn.com, pablo@...filter.org,
        nicolas.dichtel@...nd.com, razor@...ckwall.org,
        daniel@...earbox.net
Cc:     netdev@...r.kernel.org, Eyal Birger <eyal.birger@...il.com>
Subject: [PATCH ipsec] xfrm: lwtunnel: squelch kernel warning in case XFRM encap type is not available

Ido reported that a kernel warning [1] can be triggered from
user space when the kernel is compiled with CONFIG_MODULES=y and
CONFIG_XFRM=n when adding an xfrm encap type route, e.g:

$ ip route add 198.51.100.0/24 dev dummy1 encap xfrm if_id 1
Error: lwt encapsulation type not supported.

The reason for the warning is that the LWT infrastructure has an
autoloading feature which is meant only for encap types that don't
use a net device,  which is not the case in xfrm encap.

Mute this warning for xfrm encap as there's no encap module to autoload
in this case.

[1]
 WARNING: CPU: 3 PID: 2746262 at net/core/lwtunnel.c:57 lwtunnel_valid_encap_type+0x4f/0x120
[...]
 Call Trace:
  <TASK>
  rtm_to_fib_config+0x211/0x350
  inet_rtm_newroute+0x3a/0xa0
  rtnetlink_rcv_msg+0x154/0x3c0
  netlink_rcv_skb+0x49/0xf0
  netlink_unicast+0x22f/0x350
  netlink_sendmsg+0x208/0x440
  ____sys_sendmsg+0x21f/0x250
  ___sys_sendmsg+0x83/0xd0
  __sys_sendmsg+0x54/0xa0
  do_syscall_64+0x35/0x80
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reported-by: Ido Schimmel <idosch@...sch.org>
Fixes: 2c2493b9da91 ("xfrm: lwtunnel: add lwtunnel support for xfrm interfaces in collect_md mode")
Signed-off-by: Eyal Birger <eyal.birger@...il.com>
---
 net/core/lwtunnel.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/core/lwtunnel.c b/net/core/lwtunnel.c
index 6fac2f0ef074..711cd3b4347a 100644
--- a/net/core/lwtunnel.c
+++ b/net/core/lwtunnel.c
@@ -48,9 +48,11 @@ static const char *lwtunnel_encap_str(enum lwtunnel_encap_types encap_type)
 		return "RPL";
 	case LWTUNNEL_ENCAP_IOAM6:
 		return "IOAM6";
+	case LWTUNNEL_ENCAP_XFRM:
+		/* module autoload not supported for encap type */
+		return NULL;
 	case LWTUNNEL_ENCAP_IP6:
 	case LWTUNNEL_ENCAP_IP:
-	case LWTUNNEL_ENCAP_XFRM:
 	case LWTUNNEL_ENCAP_NONE:
 	case __LWTUNNEL_ENCAP_MAX:
 		/* should not have got here */
-- 
2.34.1