netdev - [PATCH] rose: check NULL rose_loopback

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Message-Id: <20220816185140.9129-1-bernard.f6bvp@gmail.com>
Date:   Tue, 16 Aug 2022 20:51:40 +0200
From:   bernard.f6bvp@...il.com
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Thomas Osterried <thomas@...erried.de>,
        Francois Romieu <romieu@...zoreil.com>
Cc:     linux-hams@...r.kernel.org, netdev@...r.kernel.org,
        Bernard <bernard.f6bvp@...il.com>, Bernard Pidoux <f6bvp@...e.fr>
Subject: [PATCH] rose: check NULL rose_loopback_neigh->loopback

From: Bernard <bernard.f6bvp@...il.com>

Since kernel 5.4.83 rose network connections were no more possible.
Last good rose module was with kernel 5.4.79.

Francois Romieu <romieu@...zoreil.com> pointed the scope of changes to
the attached commit (3b3fd068c56e3fbea30090859216a368398e39bf
in mainline, 7f0ddd41e2899349461b578bec18e8bd492e1765 in stable).

Above patch added NULL check for `rose_loopback_neigh->dev`
in rose_loopback_timer() but omitted to check rose_loopback_neigh->loopback.

It thus introduced a bug preventing ALL rose connect.
The reason is that a special rose_neigh loopback has a NULL device.

This is shown in /proc/net/rose_neigh via rose_neigh_show() function :
...
	seq_printf(seq, "%05d %-9s %-4s   %3d %3d  %3s     %3s %3lu %3lu",
	   rose_neigh->number,
	   (rose_neigh->loopback) ? "RSLOOP-0" : ax2asc(buf, &rose_neigh->callsign),
	   rose_neigh->dev ? rose_neigh->dev->name : "???",
	   rose_neigh->count,
...
/proc/net/rose_neigh displays special rose_loopback_neigh->loopback callsign RSLOOP-0:

addr  callsign  dev  count use mode restart  t0  tf digipeaters
00001 RSLOOP-0  ???      1   2  DCE     yes   0   0

By checking rose_loopback_neigh->loopback, rose_rx_call_request() is called even in case 
rose_loopback_neigh->dev is NULL. This repairs rose connections.

Verification with rose client application FPAC:

FPAC-Node v 4.1.3 (built Aug  5 2022) for LINUX (help = h)
F6BVP-4 (Commands = ?) : u
Users - AX.25 Level 2 sessions :
Port   Callsign     Callsign  AX.25 state  ROSE state  NetRom status
axudp  F6BVP-5   -> F6BVP-9   Connected    Connected   ---------

IMHO this patch should be propagated back to LTS 5.4 kernel.

Signed-off-by: Bernard Pidoux <f6bvp@...e.fr>
---
 net/rose/rose_loopback.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/rose/rose_loopback.c b/net/rose/rose_loopback.c
index 11c45c8c6c16..1c673db52636 100644
--- a/net/rose/rose_loopback.c
+++ b/net/rose/rose_loopback.c
@@ -97,8 +97,10 @@ static void rose_loopback_timer(struct timer_list *unused)

		if (frametype == ROSE_CALL_REQUEST) {
			if (!rose_loopback_neigh->dev) {
-				kfree_skb(skb);
-				continue;
+				if (!rose_loopback_neigh->loopback) {
+					kfree_skb(skb);
+					continue;
+				}
			}

			dev = rose_dev_get(dest);
--
2.34.1