dup can give a negative value

1 files changed, 5 insertions, 1 deletions

diff --git a/ftp.c b/ftp.c
index 0002abd..2ad829c 100644
--- a/ftp.c
+++ b/ftp.c
@@ -123,6 +123,7 @@ static int
 ftp_login(FTP ftp)
 {
     int sock, status;
+    int sock_wf;
 
     sock = openSocket(ftp->host, "ftp", 21);
     if (sock < 0)
@@ -169,7 +170,10 @@ ftp_login(FTP ftp)
 	}
     }
     ftp->rf = newInputStream(sock);
-    ftp->wf = fdopen(dup(sock), "wb");
+    if ((sock_wf = dup(sock)) >= 0 )
+	    ftp->wf = fdopen(sock_wf, "wb");
+    else
+	    goto open_err;
     if (!ftp->rf || !ftp->wf)
 	goto open_err;
     IStype(ftp->rf) |= IST_UNCLOSE;