From b9bfc81531a897e0160f3914152eca6be4307c3e Mon Sep 17 00:00:00 2001
From: Simon Tatham <anakin@pobox.com>
Date: Mon, 15 Oct 2018 22:26:20 +0100
Subject: [PATCH] cmdgen: fix segfault on failing to open the output file.

D'oh - simply forgot to check the return value of fopen for NULL.
---
 cmdgen.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/cmdgen.c b/cmdgen.c
index a08e7de9..5216e753 100644
--- a/cmdgen.c
+++ b/cmdgen.c
@@ -959,10 +959,15 @@ int main(int argc, char **argv)
         {
             FILE *fp;
 
-            if (outfile)
+            if (outfile) {
                 fp = f_open(outfilename, "w", FALSE);
-            else
+                if (!fp) {
+                    fprintf(stderr, "unable to open output file\n");
+                    exit(1);
+                }
+            } else {
                 fp = stdout;
+            }
 
             if (sshver == 1) {
                 ssh1_write_pubkey(fp, ssh1key);
@@ -1003,10 +1008,15 @@ int main(int argc, char **argv)
 		}
 	    }
 
-	    if (outfile)
+	    if (outfile) {
 		fp = f_open(outfilename, "w", FALSE);
-	    else
+                if (!fp) {
+                    fprintf(stderr, "unable to open output file\n");
+                    exit(1);
+                }
+            } else {
 		fp = stdout;
+            }
 	    fprintf(fp, "%s\n", fingerprint);
 	    if (outfile)
 		fclose(fp);