ash,hush: ">&10" redirects to script/tty fds should not work

The fact that shell has open fds to tty and/or scripts should be
unobservable, if possible. In particular, if redirect tries to dup
one of them via ">&script_fd", it's better to pretend that script_fd
is closed, and thus redirect fails with EBADF.

Fixes these two testcase failures:
ash-redir/redir_to_bad_fd.tests
hush-redir/redir_to_bad_fd3.tests

function                                             old     new   delta
redirect                                            1018    1129    +111
setup_redirects                                      250     359    +109
readtoken1                                          2651    2655      +4
cmdloop                                              185     187      +2
changepath                                           194     195      +1
save_fd_on_redirect                                  203     194      -9
evaltree                                             501     484     -17
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 5/2 up/down: 227/-26)           Total: 201 bytes
   text    data     bss     dec     hex filename
 914553     485    6848  921886   e111e busybox_old
 914754     485    6848  922087   e11e7 busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 30 insertions, 9 deletions

diff --git a/shell/ash.c b/shell/ash.c
index ac676c2dc..5c2e06599 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -5503,6 +5503,31 @@ save_fd_on_redirect(int fd, int avoid_fd, struct redirtab *sq)
 	return 0; /* "we did not close fd" */
 }
 
+static int
+internally_opened_fd(int fd, struct redirtab *sq)
+{
+	int i;
+#if JOBS
+	if (fd == ttyfd)
+		return 1;
+#endif
+	/* If this one of script's fds? */
+	if (fd != 0) {
+		struct parsefile *pf = g_parsefile;
+		while (pf) {
+			if (fd == pf->pf_fd)
+				return 1;
+			pf = pf->prev;
+		}
+	}
+
+	if (sq)	for (i = 0; i < sq->pair_count && sq->two_fd[i].orig_fd != EMPTY; i++) {
+		if (fd == sq->two_fd[i].moved_to)
+			return 1;
+	}
+	return 0;
+}
+
 /*
  * Process a list of redirection commands.  If the REDIR_PUSH flag is set,
  * old file descriptors are stashed away so that the redirection can be
@@ -5567,15 +5592,11 @@ redirect(union node *redir, int flags)
 				close(fd);
 			}
 		} else {
-///TODO: if _newfd_ is a script fd or saved fd, then simulate EBADF!
-//if (newfd == ttyfd) {
-//	errno = EBADF;
-//	ash_msg_and_raise_perror("A %d", newfd);
-//}
-//if (newfd == g_parsefile->pf_fd) {
-//	errno = EBADF;
-//	ash_msg_and_raise_perror("B %d", newfd);
-//}
+			/* if newfd is a script fd or saved fd, simulate EBADF */
+			if (internally_opened_fd(newfd, sv)) {
+				errno = EBADF;
+				ash_msg_and_raise_perror("%d", newfd);
+			}
 			dup2_or_raise(newfd, fd);
 			if (close_fd >= 0) /* "N>FILE" or ">&FILE" or heredoc? */
 				close(close_fd);