less: fall back to using fd #1 for keyboard reading. Closes 9231

function                                             old     new   delta
less_main                                           2535    2540      +5

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

1 files changed, 12 insertions, 4 deletions

diff --git a/miscutils/less.c b/miscutils/less.c
index d1d4a71be..877ab6ef2 100644
--- a/miscutils/less.c
+++ b/miscutils/less.c
@@ -1797,9 +1797,10 @@ int less_main(int argc, char **argv)
         /* Some versions of less can survive w/o controlling tty,
          * try to do the same. This also allows to specify an alternative
          * tty via "less 1<>TTY".
-         * We don't try to use STDOUT_FILENO directly,
+         *
+         * We prefer not to use STDOUT_FILENO directly,
          * since we want to set this fd to non-blocking mode,
-         * and not bother with restoring it on exit.
+         * and not interfere with other processes which share stdout with us.
          */
         tty_name = xmalloc_ttyname(STDOUT_FILENO);
         if (tty_name) {
@@ -1811,8 +1812,15 @@ int less_main(int argc, char **argv)
                 /* Try controlling tty */
  try_ctty:
                 tty_fd = open(CURRENT_TTY, O_RDONLY);
-                if (tty_fd < 0)
-                        return bb_cat(argv);
+                if (tty_fd < 0) {
+                        /*
+                         * If all else fails, less 481 uses stdout. Mimic that.
+                         * Testcase where usually both ttyname(STDOUT_FILENO)
+                         * and open(CURRENT_TTY) fail:
+                         * su -s /bin/sh -c 'busybox less FILE' - nobody
+                         */
+                        tty_fd = STDOUT_FILENO;
+                }
         }
         ndelay_on(tty_fd);
         kbd_fd = tty_fd; /* save in a global */