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commit ca668e35d16ca296dee1bd000de8eb8d20433a21
Author: Chuck Lever <chuck.lever@oracle.com>
Date:   Tue May 28 10:02:49 2019 -0400

    rpc.mountd: Fix mountd segfault
    
    After commit 8f459a072f93 ("Remove abuse of ai_canonname") the
    ai_canonname field in addrinfo structs returned from
    host_reliable_addrinfo() is always NULL. This results in mountd
    segfaults when there are netgroups or hostname wildcards in
    /etc/exports.
    
    Add an extra DNS query in check_wildcard() and check_netgroup() to
    obtain the client's canonical hostname instead of dereferencing
    the NULL pointer.
    
    Reported-by: Mark Wagner <mark@lanfear.net>
    Fixes: 8f459a072f93 ("Remove abuse of ai_canonname")
    Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
    Signed-off-by: Steve Dickson <steved@redhat.com>

diff --git a/support/export/client.c b/support/export/client.c
index a1fba01..ea4f89d 100644
--- a/support/export/client.c
+++ b/support/export/client.c
@@ -608,24 +608,36 @@ check_subnetwork(const nfs_client *clp, const struct addrinfo *ai)
 static int
 check_wildcard(const nfs_client *clp, const struct addrinfo *ai)
 {
-	char *cname = clp->m_hostname;
-	char *hname = ai->ai_canonname;
+	char *hname, *cname = clp->m_hostname;
 	struct hostent *hp;
 	char **ap;
+	int match;
 
-	if (wildmat(hname, cname))
-		return 1;
+	match = 0;
+
+	hname = host_canonname(ai->ai_addr);
+	if (hname == NULL)
+		goto out;
+
+	if (wildmat(hname, cname)) {
+		match = 1;
+		goto out;
+	}
 
 	/* See if hname aliases listed in /etc/hosts or nis[+]
 	 * match the requested wildcard */
 	hp = gethostbyname(hname);
 	if (hp != NULL) {
 		for (ap = hp->h_aliases; *ap; ap++)
-			if (wildmat(*ap, cname))
-				return 1;
+			if (wildmat(*ap, cname)) {
+				match = 1;
+				goto out;
+			}
 	}
 
-	return 0;
+out:
+	free(hname);
+	return match;
 }
 
 /*
@@ -645,11 +657,9 @@ check_netgroup(const nfs_client *clp, const struct addrinfo *ai)
 
 	match = 0;
 
-	hname = strdup(ai->ai_canonname);
-	if (hname == NULL) {
-		xlog(D_GENERAL, "%s: no memory for strdup", __func__);
+	hname = host_canonname(ai->ai_addr);
+	if (hname == NULL)
 		goto out;
-	}
 
 	/* First, try to match the hostname without
 	 * splitting off the domain */