From 9fb006e285ccd8cd159d8c1956e28aff94844c3a Mon Sep 17 00:00:00 2001
From: markj <markj@FreeBSD.org>
Date: Wed, 8 May 2019 16:07:43 +0000
Subject: [PATCH] MFC r346960: Retry upon NET_RT_IFLIST sysctl failure.

PR:	195191
---
 usr.sbin/rtadvd/if.c | 53 ++++++++++++++++++++++++++++++--------------
 1 file changed, 36 insertions(+), 17 deletions(-)

diff --git a/usr.sbin/rtadvd/if.c b/usr.sbin/rtadvd/if.c
index 72ea36a8f64..23fa844899b 100644
--- a/usr.sbin/rtadvd/if.c
+++ b/usr.sbin/rtadvd/if.c
@@ -406,6 +406,8 @@ update_ifinfo_nd_flags(struct ifinfo *ifi)
 	return (0);
 }
 
+#define MAX_SYSCTL_TRY 5
+
 struct ifinfo *
 update_ifinfo(struct ifilist_head_t *ifi_head, int ifindex)
 {
@@ -417,26 +419,43 @@ update_ifinfo(struct ifilist_head_t *ifi_head, int ifindex)
 	size_t len;
 	char *lim;
 	int mib[] = { CTL_NET, PF_ROUTE, 0, AF_INET6, NET_RT_IFLIST, 0 };
-	int error;
+	int error, ntry;
 
 	syslog(LOG_DEBUG, "<%s> enter", __func__);
 
-	if (sysctl(mib, sizeof(mib)/sizeof(mib[0]), NULL, &len, NULL, 0) <
-	    0) {
-		syslog(LOG_ERR,
-		    "<%s> sysctl: NET_RT_IFLIST size get failed", __func__);
-		exit(1);
-	}
-	if ((msg = malloc(len)) == NULL) {
-		syslog(LOG_ERR, "<%s> malloc failed", __func__);
-		exit(1);
-	}
-	if (sysctl(mib, sizeof(mib)/sizeof(mib[0]), msg, &len, NULL, 0) <
-	    0) {
-		syslog(LOG_ERR,
-		    "<%s> sysctl: NET_RT_IFLIST get failed", __func__);
-		exit(1);
-	}
+	ntry = 0;
+	do {
+		/*
+		 * We'll try to get addresses several times in case that
+		 * the number of addresses is unexpectedly increased during
+		 * the two sysctl calls.  This should rarely happen.
+		 * Portability note: since FreeBSD does not add margin of
+		 * memory at the first sysctl, the possibility of failure on
+		 * the second sysctl call is a bit higher.
+		 */
+
+		if (sysctl(mib, nitems(mib), NULL, &len, NULL, 0) < 0) {
+			syslog(LOG_ERR,
+			    "<%s> sysctl: NET_RT_IFLIST size get failed",
+			    __func__);
+			exit(1);
+		}
+		if ((msg = malloc(len)) == NULL) {
+			syslog(LOG_ERR, "<%s> malloc failed", __func__);
+			exit(1);
+		}
+		if (sysctl(mib, nitems(mib), msg, &len, NULL, 0) < 0) {
+			if (errno != ENOMEM || ++ntry >= MAX_SYSCTL_TRY) {
+				free(msg);
+				syslog(LOG_ERR,
+				    "<%s> sysctl: NET_RT_IFLIST get failed",
+				    __func__);
+				exit(1);
+			}
+			free(msg);
+			msg = NULL;
+		}
+	} while (msg == NULL);
 
 	lim = msg + len;
 	for (ifm = (struct if_msghdr *)msg;
-- 
2.45.0