ash: do not abort interactive mode on >&9999 redirect

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@googlemail.com>

1 files 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;