Instead of only returning a text message with GENL_SET_ERR_MSG(),
NL_SET_ERR_MSG_ATTR() can help the userspace developers by also
reporting which attribute is faulty.

When the error is specific to an attribute, NL_SET_ERR_MSG_ATTR() is now
used. The error messages have not been modified in this commit.

mptcp_userspace_pm_remove_id_zero_address() has been modified to set the
missing attribute.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm_netlink.c   | 23 ++++++++++++++---------
 net/mptcp/pm_userspace.c | 27 +++++++++++++++++----------
 2 files changed, 31 insertions(+), 19 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 98ac73938bd8196e196d5ee8c264784ba8d37645..49c34494e156ff6c3277b107c3840ee29dd3afbb 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -1403,18 +1403,21 @@ int mptcp_pm_nl_add_addr_doit(struct sk_buff *skb, struct genl_info *info)
 		return ret;
 
 	if (addr.addr.port && !address_use_port(&addr)) {
-		GENL_SET_ERR_MSG(info, "flags must have signal and not subflow when using port");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr,
+				    "flags must have signal and not subflow when using port");
 		return -EINVAL;
 	}
 
 	if (addr.flags & MPTCP_PM_ADDR_FLAG_SIGNAL &&
 	    addr.flags & MPTCP_PM_ADDR_FLAG_FULLMESH) {
-		GENL_SET_ERR_MSG(info, "flags mustn't have both signal and fullmesh");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr,
+				    "flags mustn't have both signal and fullmesh");
 		return -EINVAL;
 	}
 
 	if (addr.flags & MPTCP_PM_ADDR_FLAG_IMPLICIT) {
-		GENL_SET_ERR_MSG(info, "can't create IMPLICIT endpoint");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr,
+				    "can't create IMPLICIT endpoint");
 		return -EINVAL;
 	}
 
@@ -1608,7 +1611,7 @@ int mptcp_pm_nl_del_addr_doit(struct sk_buff *skb, struct genl_info *info)
 	spin_lock_bh(&pernet->lock);
 	entry = __lookup_addr_by_id(pernet, addr.addr.id);
 	if (!entry) {
-		GENL_SET_ERR_MSG(info, "address not found");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr, "address not found");
 		spin_unlock_bh(&pernet->lock);
 		return -EINVAL;
 	}
@@ -1790,7 +1793,7 @@ int mptcp_pm_nl_get_addr(struct sk_buff *skb, struct genl_info *info)
 	rcu_read_lock();
 	entry = __lookup_addr_by_id(pernet, addr.addr.id);
 	if (!entry) {
-		GENL_SET_ERR_MSG(info, "address not found");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr, "address not found");
 		ret = -EINVAL;
 		goto unlock_fail;
 	}
@@ -1875,7 +1878,8 @@ static int parse_limit(struct genl_info *info, int id, unsigned int *limit)
 
 	*limit = nla_get_u32(attr);
 	if (*limit > MPTCP_PM_ADDR_MAX) {
-		GENL_SET_ERR_MSG(info, "limit greater than maximum");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr,
+				    "limit greater than maximum");
 		return -EINVAL;
 	}
 	return 0;
@@ -2003,7 +2007,8 @@ int mptcp_pm_nl_set_flags(struct sk_buff *skb, struct genl_info *info)
 	if (addr.addr.family == AF_UNSPEC) {
 		lookup_by_id = 1;
 		if (!addr.addr.id) {
-			GENL_SET_ERR_MSG(info, "missing required inputs");
+			NL_SET_ERR_MSG_ATTR(info->extack, attr,
+					    "missing required inputs");
 			return -EOPNOTSUPP;
 		}
 	}
@@ -2016,13 +2021,13 @@ int mptcp_pm_nl_set_flags(struct sk_buff *skb, struct genl_info *info)
 			       __lookup_addr(pernet, &addr.addr);
 	if (!entry) {
 		spin_unlock_bh(&pernet->lock);
-		GENL_SET_ERR_MSG(info, "address not found");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr, "address not found");
 		return -EINVAL;
 	}
 	if ((addr.flags & MPTCP_PM_ADDR_FLAG_FULLMESH) &&
 	    (entry->flags & MPTCP_PM_ADDR_FLAG_SIGNAL)) {
 		spin_unlock_bh(&pernet->lock);
-		GENL_SET_ERR_MSG(info, "invalid addr flags");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr, "invalid addr flags");
 		return -EINVAL;
 	}
 
diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index a3d477059b11c3a5618dbb6256434a8e55845995..72d4861e497eef5a516fc1c3ec1659807ffedd53 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -190,7 +190,8 @@ static struct mptcp_sock *mptcp_userspace_pm_get_sock(const struct genl_info *in
 	}
 
 	if (!mptcp_pm_is_userspace(msk)) {
-		GENL_SET_ERR_MSG(info, "invalid request; userspace PM not selected");
+		NL_SET_ERR_MSG_ATTR(info->extack, token,
+				    "invalid request; userspace PM not selected");
 		sock_put((struct sock *)msk);
 		return NULL;
 	}
@@ -224,14 +225,16 @@ int mptcp_pm_nl_announce_doit(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	if (addr_val.addr.id == 0 || !(addr_val.flags & MPTCP_PM_ADDR_FLAG_SIGNAL)) {
-		GENL_SET_ERR_MSG(info, "invalid addr id or flags");
+		NL_SET_ERR_MSG_ATTR(info->extack, addr,
+				    "invalid addr id or flags");
 		err = -EINVAL;
 		goto announce_err;
 	}
 
 	err = mptcp_userspace_pm_append_new_local_addr(msk, &addr_val, false);
 	if (err < 0) {
-		GENL_SET_ERR_MSG(info, "did not match address and id");
+		NL_SET_ERR_MSG_ATTR(info->extack, addr,
+				    "did not match address and id");
 		goto announce_err;
 	}
 
@@ -254,7 +257,8 @@ int mptcp_pm_nl_announce_doit(struct sk_buff *skb, struct genl_info *info)
 }
 
 static int mptcp_userspace_pm_remove_id_zero_address(struct mptcp_sock *msk,
-						     struct genl_info *info)
+						     struct genl_info *info,
+						     struct nlattr *attr)
 {
 	struct mptcp_rm_list list = { .nr = 0 };
 	struct mptcp_subflow_context *subflow;
@@ -270,7 +274,8 @@ static int mptcp_userspace_pm_remove_id_zero_address(struct mptcp_sock *msk,
 		}
 	}
 	if (!has_id_0) {
-		GENL_SET_ERR_MSG(info, "address with id 0 not found");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr,
+				    "address with id 0 not found");
 		goto remove_err;
 	}
 
@@ -330,7 +335,7 @@ int mptcp_pm_nl_remove_doit(struct sk_buff *skb, struct genl_info *info)
 	sk = (struct sock *)msk;
 
 	if (id_val == 0) {
-		err = mptcp_userspace_pm_remove_id_zero_address(msk, info);
+		err = mptcp_userspace_pm_remove_id_zero_address(msk, info, id);
 		goto out;
 	}
 
@@ -339,7 +344,8 @@ int mptcp_pm_nl_remove_doit(struct sk_buff *skb, struct genl_info *info)
 	spin_lock_bh(&msk->pm.lock);
 	match = mptcp_userspace_pm_lookup_addr_by_id(msk, id_val);
 	if (!match) {
-		GENL_SET_ERR_MSG(info, "address with specified id not found");
+		NL_SET_ERR_MSG_ATTR(info->extack, id,
+				    "address with specified id not found");
 		spin_unlock_bh(&msk->pm.lock);
 		release_sock(sk);
 		goto out;
@@ -389,7 +395,7 @@ int mptcp_pm_nl_subflow_create_doit(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	if (entry.flags & MPTCP_PM_ADDR_FLAG_SIGNAL) {
-		GENL_SET_ERR_MSG(info, "invalid addr flags");
+		NL_SET_ERR_MSG_ATTR(info->extack, laddr, "invalid addr flags");
 		err = -EINVAL;
 		goto create_err;
 	}
@@ -409,7 +415,8 @@ int mptcp_pm_nl_subflow_create_doit(struct sk_buff *skb, struct genl_info *info)
 
 	err = mptcp_userspace_pm_append_new_local_addr(msk, &entry, false);
 	if (err < 0) {
-		GENL_SET_ERR_MSG(info, "did not match address and id");
+		NL_SET_ERR_MSG_ATTR(info->extack, laddr,
+				    "did not match address and id");
 		goto create_err;
 	}
 
@@ -702,7 +709,7 @@ int mptcp_userspace_pm_get_addr(struct sk_buff *skb,
 	spin_lock_bh(&msk->pm.lock);
 	entry = mptcp_userspace_pm_lookup_addr_by_id(msk, addr.addr.id);
 	if (!entry) {
-		GENL_SET_ERR_MSG(info, "address not found");
+		NL_SET_ERR_MSG_ATTR(info->extack, attr, "address not found");
 		ret = -EINVAL;
 		goto unlock_fail;
 	}

-- 
2.47.1