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.

4 files changed, 48 insertions, 4 deletions

diff --git a/NEWS b/NEWS
index 4c8e162c7..3ed44b284 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,11 @@ GNU coreutils NEWS                                    -*- outline -*-
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+** Bug fixes
+
+  tac no longer fails to handle two or more non-seekable inputs
+  [bug introduced in coreutils-5.3.0]
+
 
 * Noteworthy changes in release 8.14 (2011-10-12) [stable]
 
diff --git a/src/tac.c b/src/tac.c
index 16b918303..2898199a2 100644
--- a/src/tac.c
+++ b/src/tac.c
@@ -447,12 +447,13 @@ copy_to_temp (FILE **g_tmp, char **g_tempfile, int input_fd, char const *file)
      FIXME: clean up upon fatal signal.  Don't block them, in case
      $TMPFILE is a remote file system.  */
 
-  char *tempfile = template;
-  int fd = mkstemp (template);
+  char *tempfile = xstrdup (template);
+  int fd = mkstemp (tempfile);
   if (fd < 0)
     {
       error (0, errno, _("cannot create temporary file in %s"),
              quote (tempdir));
+      free (tempfile);
       return false;
     }
 
@@ -462,6 +463,7 @@ copy_to_temp (FILE **g_tmp, char **g_tempfile, int input_fd, char const *file)
       error (0, errno, _("cannot open %s for writing"), quote (tempfile));
       close (fd);
       unlink (tempfile);
+      free (tempfile);
       return false;
     }
 
@@ -497,6 +499,7 @@ copy_to_temp (FILE **g_tmp, char **g_tempfile, int input_fd, char const *file)
 
  Fail:
   fclose (tmp);
+  free (tempfile);
   return false;
 }
 
@@ -508,8 +511,16 @@ tac_nonseekable (int input_fd, const char *file)
 {
   FILE *tmp_stream;
   char *tmp_file;
-  return (copy_to_temp (&tmp_stream, &tmp_file, input_fd, file)
-          && tac_seekable (fileno (tmp_stream), tmp_file));
+  if (copy_to_temp (&tmp_stream, &tmp_file, input_fd, file))
+    {
+      if (tac_seekable (fileno (tmp_stream), tmp_file))
+        {
+          free (tmp_file);
+          return true;
+        }
+    }
+
+  return false;
 }
 
 /* Print FILE in reverse, copying it to a temporary
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 9c9a1b8c1..5021c1844 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -274,6 +274,7 @@ TESTS =						\
   misc/sum-sysv					\
   misc/tac					\
   misc/tac-continue				\
+  misc/tac-2-nonseekable			\
   misc/tail					\
   misc/tee					\
   misc/tee-dash					\
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