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Date:      Tue, 30 Apr 2019 14:44:40 +0000 (UTC)
From:      Mark Johnston <markj@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r346960 - head/usr.sbin/rtadvd
Message-ID:  <201904301444.x3UEieAU088107@repo.freebsd.org>
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Author: markj
Date: Tue Apr 30 14:44:39 2019
New Revision: 346960
URL: https://svnweb.freebsd.org/changeset/base/346960

Log:
  Retry upon NET_RT_IFLIST sysctl failure.
  
  Port the logic used by getifaddrs(3) to handle the case where
  NET_RT_IFLIST returns ENOMEM, which can occur if the list size changes
  between the buffer allocation and sysctl read.
  
  PR:		195191
  Submitted by:	Guy Yur <guyyur@gmail.com> (original version)
  MFC after:	1 week

Modified:
  head/usr.sbin/rtadvd/if.c

Modified: head/usr.sbin/rtadvd/if.c
==============================================================================
--- head/usr.sbin/rtadvd/if.c	Tue Apr 30 14:29:09 2019	(r346959)
+++ head/usr.sbin/rtadvd/if.c	Tue Apr 30 14:44:39 2019	(r346960)
@@ -408,6 +408,8 @@ 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)
 {
@@ -419,26 +421,43 @@ update_ifinfo(struct ifilist_head_t *ifi_head, int ifi
 	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;

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