From: Luka Gejak <luka.gejak@linux.dev>

In hsr_newlink(), a provided but invalid IFLA_HSR_INTERLINK attribute
was silently ignored if __dev_get_by_index() returned NULL. This leads
to incorrect RedBox topology creation without notifying the user.

Fix this by returning -EINVAL and an extack message when the
interlink attribute is present but cannot be resolved.

Reviewed-by: Felix Maurer <fmaurer@redhat.com>
Signed-off-by: Luka Gejak <luka.gejak@linux.dev>
---
 net/hsr/hsr_netlink.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/hsr/hsr_netlink.c b/net/hsr/hsr_netlink.c
index db0b0af7a692..f0ca23da3ab9 100644
--- a/net/hsr/hsr_netlink.c
+++ b/net/hsr/hsr_netlink.c
@@ -76,9 +76,14 @@ static int hsr_newlink(struct net_device *dev,
 		return -EINVAL;
 	}
 
-	if (data[IFLA_HSR_INTERLINK])
+	if (data[IFLA_HSR_INTERLINK]) {
 		interlink = __dev_get_by_index(link_net,
 					       nla_get_u32(data[IFLA_HSR_INTERLINK]));
+		if (!interlink) {
+			NL_SET_ERR_MSG_MOD(extack, "Interlink does not exist");
+			return -EINVAL;
+		}
+	}
 
 	if (interlink && interlink == link[0]) {
 		NL_SET_ERR_MSG_MOD(extack, "Interlink and Slave1 are the same");
-- 
2.53.0