netdev - [v2] ioctl: only memset non-NULL link settings

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Message-Id: <20200827095033.3265848-1-hegtvedt@cisco.com>
Date:   Thu, 27 Aug 2020 11:50:33 +0200
From:   Hans-Christian Noren Egtvedt <hegtvedt@...co.com>
To:     netdev@...r.kernel.org
Cc:     Hans-Christian Noren Egtvedt <hegtvedt@...co.com>
Subject: [v2] ioctl: only memset non-NULL link settings

In commit bef780467fa ('ioctl: do not pass transceiver value back to
kernel') a regression slipped in. If we have a kernel that does not
support the ETHTOOL_xLINKSETTINGS API, then the do_ioctl_glinksettings()
function will return a NULL pointer.

Hence before memset'ing the pointer to zero we must first check it is
valid, as NULL return is perfectly fine when running on old kernels.

Fixes: bef780467fa7 ("ioctl: do not pass transceiver value back to kernel")
Signed-off-by: Hans-Christian Noren Egtvedt <hegtvedt@...co.com>
---
 ethtool.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/ethtool.c b/ethtool.c
index e32a93b..606af3e 100644
--- a/ethtool.c
+++ b/ethtool.c
@@ -3048,10 +3048,11 @@ static int do_sset(struct cmd_context *ctx)
 		struct ethtool_link_usettings *link_usettings;
 
 		link_usettings = do_ioctl_glinksettings(ctx);
-		memset(&link_usettings->deprecated, 0,
-		       sizeof(link_usettings->deprecated));
 		if (link_usettings == NULL)
 			link_usettings = do_ioctl_gset(ctx);
+		else
+			memset(&link_usettings->deprecated, 0,
+			       sizeof(link_usettings->deprecated));
 		if (link_usettings == NULL) {
 			perror("Cannot get current device settings");
 			err = -1;
-- 
2.25.1