[PATCH 5.4 15/77] rose: check NULL rose_loopback_neigh->loopback

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Bernard Pidoux <f6bvp@free.fr>

[ Upstream commit 3c53cd65dece47dd1f9d3a809f32e59d1d87b2b8 ]

Commit 3b3fd068c56e3fbea30090859216a368398e39bf added NULL check for
`rose_loopback_neigh->dev` in rose_loopback_timer() but omitted to
check rose_loopback_neigh->loopback.

It thus prevents *all* rose connect.

The reason is that a special rose_neigh loopback has a NULL device.

/proc/net/rose_neigh illustrates it 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 as
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   ---------

Fixes: 3b3fd068c56e ("rose: Fix Null pointer dereference in rose_send_frame()")
Signed-off-by: Bernard Pidoux <f6bvp@free.fr>
Suggested-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Thomas DL9SAU Osterried <thomas@osterried.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/rose/rose_loopback.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/rose/rose_loopback.c b/net/rose/rose_loopback.c
index 11c45c8c6c164..036d92c0ad794 100644
--- a/net/rose/rose_loopback.c
+++ b/net/rose/rose_loopback.c
@@ -96,7 +96,8 @@ static void rose_loopback_timer(struct timer_list *unused)
 		}
 
 		if (frametype == ROSE_CALL_REQUEST) {
-			if (!rose_loopback_neigh->dev) {
+			if (!rose_loopback_neigh->dev &&
+			    !rose_loopback_neigh->loopback) {
 				kfree_skb(skb);
 				continue;
 			}
-- 
2.35.1