wifi: cfg80211: report per-link errors during association

When one of the links (other than the assoc_link) is misconfigured
and cannot work the association will fail. However, userspace was not
able to tell that the operation only failed because of a problem with
one of the links. Fix this, by allowing the driver to set a per-link
error code and reporting the (first) offending link by setting the
bad_attr accordingly.

This only allows us to report the first error, but that is sufficient
for userspace to e.g. remove the offending link and retry.
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230920211508.ebe63c0bd513.I40799998f02bf987acee1501a2522dc98bb6eb5a@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -2980,12 +2980,15 @@ struct cfg80211_auth_request {
  * @elems_len: length of the elements
  * @disabled: If set this link should be included during association etc. but it
  *	should not be used until enabled by the AP MLD.
+ * @error: per-link error code, must be <= 0. If there is an error, then the
+ *	operation as a whole must fail.
  */
 struct cfg80211_assoc_link {
 	struct cfg80211_bss *bss;
 	const u8 *elems;
 	size_t elems_len;
 	bool disabled;
+	int error;
 };
 
 /**

net/wireless/nl80211.c

@@ -10941,8 +10941,9 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
 
 		if (cfg80211_find_ext_elem(WLAN_EID_EXT_NON_INHERITANCE,
 					   req.ie, req.ie_len)) {
-			GENL_SET_ERR_MSG(info,
-					 "non-inheritance makes no sense");
+			NL_SET_ERR_MSG_ATTR(info->extack,
+					    info->attrs[NL80211_ATTR_IE],
+					    "non-inheritance makes no sense");
 			return -EINVAL;
 		}
 	}
@@ -11067,6 +11068,7 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
 
 			if (!attrs[NL80211_ATTR_MLO_LINK_ID]) {
 				err = -EINVAL;
+				NL_SET_BAD_ATTR(info->extack, link);
 				goto free;
 			}
 
@@ -11074,6 +11076,7 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
 			/* cannot use the same link ID again */
 			if (req.links[link_id].bss) {
 				err = -EINVAL;
+				NL_SET_BAD_ATTR(info->extack, link);
 				goto free;
 			}
 			req.links[link_id].bss =
@@ -11081,6 +11084,8 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
 			if (IS_ERR(req.links[link_id].bss)) {
 				err = PTR_ERR(req.links[link_id].bss);
 				req.links[link_id].bss = NULL;
+				NL_SET_ERR_MSG_ATTR(info->extack,
+						    link, "Error fetching BSS for link");
 				goto free;
 			}
 
@@ -11093,8 +11098,9 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
 				if (cfg80211_find_elem(WLAN_EID_FRAGMENT,
 						       req.links[link_id].elems,
 						       req.links[link_id].elems_len)) {
-					GENL_SET_ERR_MSG(info,
-							 "cannot deal with fragmentation");
+					NL_SET_ERR_MSG_ATTR(info->extack,
+							    attrs[NL80211_ATTR_IE],
+							    "cannot deal with fragmentation");
 					err = -EINVAL;
 					goto free;
 				}
@@ -11102,8 +11108,9 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
 				if (cfg80211_find_ext_elem(WLAN_EID_EXT_NON_INHERITANCE,
 							   req.links[link_id].elems,
 							   req.links[link_id].elems_len)) {
-					GENL_SET_ERR_MSG(info,
-							 "cannot deal with non-inheritance");
+					NL_SET_ERR_MSG_ATTR(info->extack,
+							    attrs[NL80211_ATTR_IE],
+							    "cannot deal with non-inheritance");
 					err = -EINVAL;
 					goto free;
 				}
@@ -11146,6 +11153,9 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
 
 	err = nl80211_crypto_settings(rdev, info, &req.crypto, 1);
 	if (!err) {
+		struct nlattr *link;
+		int rem = 0;
+
 		err = cfg80211_mlme_assoc(rdev, dev, &req);
 
 		if (!err && info->attrs[NL80211_ATTR_SOCKET_OWNER]) {
@@ -11154,6 +11164,34 @@ static int nl80211_associate(struct sk_buff *skb, struct genl_info *info)
 			memcpy(dev->ieee80211_ptr->disconnect_bssid,
 			       ap_addr, ETH_ALEN);
 		}
+
+		/* Report error from first problematic link */
+		if (info->attrs[NL80211_ATTR_MLO_LINKS]) {
+			nla_for_each_nested(link,
+					    info->attrs[NL80211_ATTR_MLO_LINKS],
+					    rem) {
+				struct nlattr *link_id_attr =
+					nla_find_nested(link, NL80211_ATTR_MLO_LINK_ID);
+
+				if (!link_id_attr)
+					continue;
+
+				link_id = nla_get_u8(link_id_attr);
+
+				if (link_id == req.link_id)
+					continue;
+
+				if (!req.links[link_id].error ||
+				    WARN_ON(req.links[link_id].error > 0))
+					continue;
+
+				WARN_ON(err >= 0);
+
+				NL_SET_BAD_ATTR(info->extack, link);
+				err = req.links[link_id].error;
+				break;
+			}
+		}
 	}
 
 free: