Handle getlogin failure in PTY.spawn

getlogin is only called if USER environment variable is not set,
but if getlogin returns NULL in that case, then do not call
getpwnam, and assume /bin/sh as shell.

Mentioned in comment to bug 20586.

1 files changed, 7 insertions, 3 deletions

diff --git a/ext/pty/pty.c b/ext/pty/pty.c
index 5ca55e41d6..49caa0b79f 100644
--- a/ext/pty/pty.c
+++ b/ext/pty/pty.c
@@ -215,9 +215,13 @@ establishShell(int argc, VALUE *argv, struct pty_info *info,
         else {
 #if defined HAVE_PWD_H
             const char *username = getenv("USER");
-            struct passwd *pwent = getpwnam(username ? username : getlogin());
-            if (pwent && pwent->pw_shell)
-                shellname = pwent->pw_shell;
+            if (username == NULL)
+                username = getlogin();
+            if (username != NULL) {
+                struct passwd *pwent = getpwnam(username);
+                if (pwent && pwent->pw_shell)
+                    shellname = pwent->pw_shell;
+            }
 #endif
         }
         v = rb_str_new2(shellname);