exec_pty: Treat a socketpair for stdin/stdout same as a pipe for ksh

Sudo will run a command that is part of a pipeline in the background.
However, ksh appears to use a socketpair instead of a pipe for this
which broke sudo's heuristic.  With this change, a command like
    $ sudo cat /etc/services | head -3
will avoid setting the terminal to raw mode in ksh, which matches
the behavior of other shells.

Author: millert

src/exec_pty.c

@@ -1241,7 +1241,7 @@ exec_pty(struct command_details *details,
 	    /* Not logging stdin, do not interpose. */
 	    sudo_debug_printf(SUDO_DEBUG_INFO,
 		"stdin not user's tty, not logging");
-	    if (S_ISFIFO(sb.st_mode))
+	    if (S_ISFIFO(sb.st_mode) || S_ISSOCK(sb.st_mode))
 		SET(details->flags, CD_EXEC_BG);
 	    io_fds[SFD_STDIN] = dup(STDIN_FILENO);
 	    if (io_fds[SFD_STDIN] == -1)
@@ -1273,7 +1273,7 @@ exec_pty(struct command_details *details,
 	    /* Not logging stdout, do not interpose. */
 	    sudo_debug_printf(SUDO_DEBUG_INFO,
 		"stdout not user's tty, not logging");
-	    if (S_ISFIFO(sb.st_mode)) {
+	    if (S_ISFIFO(sb.st_mode) || S_ISSOCK(sb.st_mode)) {
 		SET(details->flags, CD_EXEC_BG);
 		term_raw_flags = SUDO_TERM_OFLAG;
 	    }