[PATCH ethtool] Fix segfault with cable test and ./configure --disable-netlink

[Andrew Lunn <andrew@lunn.ch>]

When the netlink interface code is disabled, a stub version of
netlink_run_handler() is used. This stub version needs to handle the
case when there is no possibility for a command to fall back to the
IOCTL call. The two cable tests commands have no such fallback, and if
we don't handle this, ethtool tries to jump through a NULL pointer
resulting in a segfault.

Reported-by: Chris Healy <cphealy@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---
 netlink/extapi.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/netlink/extapi.h b/netlink/extapi.h
index c5bfde9..a35d5f2 100644
--- a/netlink/extapi.h
+++ b/netlink/extapi.h
@@ -46,6 +46,12 @@ void nl_monitor_usage(void);
 static inline void netlink_run_handler(struct cmd_context *ctx,
 				       nl_func_t nlfunc, bool no_fallback)
 {
+	if (no_fallback) {
+		fprintf(stderr,
+			"Command requires kernel netlink support which is not "
+			"enabled in this ethtool binary\n");
+		exit(1);
+	}
 }
 
 static inline int nl_monitor(struct cmd_context *ctx)
-- 
2.27.0