Patch "rtnetlink: return ENODEV when ifname does not exist and group is given" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    rtnetlink: return ENODEV when ifname does not exist and group is given

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     rtnetlink-return-enodev-when-ifname-does-not-exist-a.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d63c94c896b118081b0e92be0fd41f78224b035f
Author: Florent Fourcot <florent.fourcot@xxxxxxxxxx>
Date:   Fri Apr 15 18:53:27 2022 +0200

    rtnetlink: return ENODEV when ifname does not exist and group is given
    
    [ Upstream commit ef2a7c9065cea4e3fbc0390e82d05141abbccd7f ]
    
    When the interface does not exist, and a group is given, the given
    parameters are being set to all interfaces of the given group. The given
    IFNAME/ALT_IF_NAME are being ignored in that case.
    
    That can be dangerous since a typo (or a deleted interface) can produce
    weird side effects for caller:
    
    Case 1:
    
     IFLA_IFNAME=valid_interface
     IFLA_GROUP=1
     MTU=1234
    
    Case 1 will update MTU and group of the given interface "valid_interface".
    
    Case 2:
    
     IFLA_IFNAME=doesnotexist
     IFLA_GROUP=1
     MTU=1234
    
    Case 2 will update MTU of all interfaces in group 1. IFLA_IFNAME is
    ignored in this case
    
    This behaviour is not consistent and dangerous. In order to fix this issue,
    we now return ENODEV when the given IFNAME does not exist.
    
    Signed-off-by: Florent Fourcot <florent.fourcot@xxxxxxxxxx>
    Signed-off-by: Brian Baboch <brian.baboch@xxxxxxxxxx>
    Reviewed-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Stable-dep-of: 30188bd7838c ("rtnetlink: Reject negative ifindexes in RTM_NEWLINK")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index cee86a2b3a036..ffa97613314ff 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -3272,6 +3272,7 @@ static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 	struct ifinfomsg *ifm;
 	char ifname[IFNAMSIZ];
 	struct nlattr **data;
+	bool link_specified;
 	int err;
 
 #ifdef CONFIG_MODULES
@@ -3292,12 +3293,16 @@ static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 		ifname[0] = '\0';
 
 	ifm = nlmsg_data(nlh);
-	if (ifm->ifi_index > 0)
+	if (ifm->ifi_index > 0) {
+		link_specified = true;
 		dev = __dev_get_by_index(net, ifm->ifi_index);
-	else if (tb[IFLA_IFNAME] || tb[IFLA_ALT_IFNAME])
+	} else if (tb[IFLA_IFNAME] || tb[IFLA_ALT_IFNAME]) {
+		link_specified = true;
 		dev = rtnl_dev_get(net, NULL, tb[IFLA_ALT_IFNAME], ifname);
-	else
+	} else {
+		link_specified = false;
 		dev = NULL;
+	}
 
 	master_dev = NULL;
 	m_ops = NULL;
@@ -3400,7 +3405,12 @@ static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 	}
 
 	if (!(nlh->nlmsg_flags & NLM_F_CREATE)) {
-		if (ifm->ifi_index == 0 && tb[IFLA_GROUP])
+		/* No dev found and NLM_F_CREATE not set. Requested dev does not exist,
+		 * or it's for a group
+		*/
+		if (link_specified)
+			return -ENODEV;
+		if (tb[IFLA_GROUP])
 			return rtnl_group_changelink(skb, net,
 						nla_get_u32(tb[IFLA_GROUP]),
 						ifm, extack, tb);