[git commit] ash: do not abort interactive mode on >&9999 redirect

[Denys Vlasenko]

commit: https://git.busybox.net/busybox/commit/?id=0829fce079dae45737330114c27886cb8af85043
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master

With very large fd#, the error code path is different
from one for closed but small fd#.

Make it not abort if we are interactive:

$ echo text >&99    # this wasn't buggy
ash: dup2(9,1): Bad file descriptor
$ echo text >&9999  # this was
ash: fcntl(1,F_DUPFD,10000): Invalid argument

function                                             old     new   delta
.rodata                                           105637  105661     +24
dup2_or_raise                                         35      38      +3
redirect                                            1084    1044     -40
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 27/-40)            Total: -13 bytes

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 shell/ash.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/shell/ash.c b/shell/ash.c
index 094a87390..39455c7c5 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -5621,10 +5621,13 @@ dup2_or_raise(int from, int to)
 	newfd = (from != to) ? dup2(from, to) : to;
 	if (newfd < 0) {
 		/* Happens when source fd is not open: try "echo >&99" */
-		ash_msg_and_raise_perror("%d", from);
+		ash_msg_and_raise_perror("dup2(%d,%d)", from, to);
 	}
 	return newfd;
 }
+/* The only possible error return is EBADF (fd wasn't open).
+ * Transient errors retry, other errors raise exception.
+ */
 static int
 dup_CLOEXEC(int fd, int avoid_fd)
 {
@@ -5639,6 +5642,16 @@ dup_CLOEXEC(int fd, int avoid_fd)
 			goto repeat;
 		if (errno == EINTR)
 			goto repeat;
+		if (errno != EBADF) {
+			/* "echo >&9999" gets EINVAL trying to save fd 1 to above 9999.
+			 * We could try saving it _below_ 9999 instead (how?), but
+			 * this probably means that dup2(9999,1) to effectuate >&9999
+			 * would also not work: fd 9999 can't exist. Gracefully bail out.
+			 * (This differs from "echo >&99" where saving works, but
+			 * subsequent dup2(99,1) fails if fd 99 is not open).
+			 */
+			ash_msg_and_raise_perror("fcntl(%d,F_DUPFD,%d)", fd, avoid_fd + 1);
+		}
 	}
 	return newfd;
 }
@@ -5754,7 +5767,7 @@ save_fd_on_redirect(int fd, int avoid_fd, struct redirtab *sq)
 			new_fd = dup_CLOEXEC(fd, avoid_fd);
 			sq->two_fd[i].moved_to = new_fd;
 			TRACE(("redirect_fd %d: already busy, moving to %d\n", fd, new_fd));
-			if (new_fd < 0) /* what? */
+			if (new_fd < 0) /* EBADF? what? */
 				xfunc_die();
 			return 0; /* "we did not close fd" */
 		}
@@ -5769,8 +5782,7 @@ save_fd_on_redirect(int fd, int avoid_fd, struct redirtab *sq)
 	new_fd = dup_CLOEXEC(fd, avoid_fd);
 	TRACE(("redirect_fd %d: previous fd is moved to %d (-1 if it was closed)\n", fd, new_fd));
 	if (new_fd < 0) {
-		if (errno != EBADF)
-			xfunc_die();
+		/* EBADF (fd is not open) */
 		/* new_fd = CLOSED; - already is -1 */
 	}
 	sq->two_fd[i].moved_to = new_fd;