From 40432e6eb37d62dabbf4416f3062cdf2a2fa1b40 Mon Sep 17 00:00:00 2001
From: Johannes Berg <johannes.berg@intel.com>
Date: Thu, 11 Oct 2018 15:55:49 +0200
Subject: [PATCH] nl80211: Implement netlink extended ACK support

Implement netlink extended ACK support to print out the error
message (if any).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 src/drivers/driver_nl80211.c | 57 +++++++++++++++++++++++++++++++++++-
 1 file changed, 56 insertions(+), 1 deletion(-)

diff --git a/src/drivers/driver_nl80211.c b/src/drivers/driver_nl80211.c
index 39a02d3ee..b26894f83 100644
--- a/src/drivers/driver_nl80211.c
+++ b/src/drivers/driver_nl80211.c
@@ -40,6 +40,29 @@
 #include "driver_nl80211.h"
 
 
+/* support for extack if compilation headers are too old */
+#ifndef NETLINK_EXT_ACK
+#define NETLINK_EXT_ACK 11
+enum nlmsgerr_attrs {
+	NLMSGERR_ATTR_UNUSED,
+	NLMSGERR_ATTR_MSG,
+	NLMSGERR_ATTR_OFFS,
+	NLMSGERR_ATTR_COOKIE,
+
+	__NLMSGERR_ATTR_MAX,
+	NLMSGERR_ATTR_MAX = __NLMSGERR_ATTR_MAX - 1
+};
+#endif
+#ifndef NLM_F_CAPPED
+#define NLM_F_CAPPED 0x100
+#endif
+#ifndef NLM_F_ACK_TLVS
+#define NLM_F_ACK_TLVS 0x200
+#endif
+#ifndef SOL_NETLINK
+#define SOL_NETLINK 270
+#endif
+
 #ifndef CONFIG_LIBNL20
 /*
  * libnl 1.1 has a bug, it tries to allocate socket numbers densely
@@ -302,8 +325,35 @@ static int finish_handler(struct nl_msg *msg, void *arg)
 static int error_handler(struct sockaddr_nl *nla, struct nlmsgerr *err,
 			 void *arg)
 {
+	struct nlmsghdr *nlh = (struct nlmsghdr *) err - 1;
+	int len = nlh->nlmsg_len;
+	struct nlattr *attrs;
+	struct nlattr *tb[NLMSGERR_ATTR_MAX + 1];
 	int *ret = arg;
+	int ack_len = sizeof(*nlh) + sizeof(int) + sizeof(*nlh);
+
 	*ret = err->error;
+
+	if (!(nlh->nlmsg_flags & NLM_F_ACK_TLVS))
+		return NL_SKIP;
+
+	if (!(nlh->nlmsg_flags & NLM_F_CAPPED))
+		ack_len += err->msg.nlmsg_len - sizeof(*nlh);
+
+	if (len <= ack_len)
+		return NL_STOP;
+
+	attrs = (void *) ((unsigned char *) nlh + ack_len);
+	len -= ack_len;
+
+	nla_parse(tb, NLMSGERR_ATTR_MAX, attrs, len, NULL);
+	if (tb[NLMSGERR_ATTR_MSG]) {
+		len = strnlen((char *) nla_data(tb[NLMSGERR_ATTR_MSG]),
+			      nla_len(tb[NLMSGERR_ATTR_MSG]));
+		wpa_printf(MSG_ERROR, "nl80211: kernel reports: %*s",
+			   len, (char *) nla_data(tb[NLMSGERR_ATTR_MSG]));
+	}
+
 	return NL_SKIP;
 }
 
@@ -342,7 +392,7 @@ static int send_and_recv(struct nl80211_global *global,
 			 void *valid_data)
 {
 	struct nl_cb *cb;
-	int err = -ENOMEM;
+	int err = -ENOMEM, opt;
 
 	if (!msg)
 		return -ENOMEM;
@@ -351,6 +401,11 @@ static int send_and_recv(struct nl80211_global *global,
 	if (!cb)
 		goto out;
 
+	/* try to set NETLINK_EXT_ACK to 1, ignoring errors */
+	opt = 1;
+	setsockopt(nl_socket_get_fd(nl_handle), SOL_NETLINK,
+		   NETLINK_EXT_ACK, &opt, sizeof(opt));
+
 	err = nl_send_auto_complete(nl_handle, msg);
 	if (err < 0)
 		goto out;