tac: don't misbehave with multiple non-seekable inputs

* src/tac.c (copy_to_temp): Do not reuse the template buffer.
Instead, scribble only on a freshly-xstrdup'd copy each time.
Free that buffer both here, upon failure, and ...
(tac_nonseekable): ...free the buffer in caller, upon success.
* tests/misc/tac-2-nonseekable: New file.
* tests/Makefile.am (TESTS): Add it.
* NEWS (Bug fixes): Mention it.
Reported by Ambrose Feinstein in http://debbugs.gnu.org/9762.

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/misc/tac-2-nonseekable b/tests/misc/tac-2-nonseekable
new file mode 100755
index 000000000..7b4877367
--- /dev/null
+++ b/tests/misc/tac-2-nonseekable
@@ -0,0 +1,27 @@
+#!/bin/sh
+# ensure that tac works with two or more non-seekable inputs
+
+# Copyright (C) 2011 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/init.sh"; path_prepend_ ../src
+print_ver_ tac
+
+echo x | tac - - > out 2> err || fail=1
+echo x > exp || fail=1
+compare out exp || fail=1
+compare err /dev/null || fail=1
+
+Exit $fail