Re: [syzbot] general protection fault in phy_start_cable_test_tdr

[syzbot <syzbot+5cf270e2069645b6bd2c@syzkaller.appspotmail.com>]

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Subject: general protection fault in phy_start_cable_test_tdr
Author: djahchankoike@gmail.com

#syz test

In ethnl_act_cable_test_tdr, phydev is tested for the condition of being
null or an error by checking IS_ERR_OR_NULL, however the result is being
negated and lets a null phydev go through. Simply removing the logical
NOT on the conditional suffices.
---
 net/ethtool/cabletest.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ethtool/cabletest.c b/net/ethtool/cabletest.c
index d365ad5f5434..f25da884b3dd 100644
--- a/net/ethtool/cabletest.c
+++ b/net/ethtool/cabletest.c
@@ -346,7 +346,7 @@ int ethnl_act_cable_test_tdr(struct sk_buff *skb, struct genl_info *info)
 	phydev = ethnl_req_get_phydev(&req_info,
 				      tb[ETHTOOL_A_CABLE_TEST_TDR_HEADER],
 				      info->extack);
-	if (!IS_ERR_OR_NULL(phydev)) {
+	if (IS_ERR_OR_NULL(phydev)) {
 		ret = -EOPNOTSUPP;
 		goto out_dev_put;
 	}
-- 
2.43.0