[PATCH] maint.mk: add syntax-check to avoid char[PATH_MAX]

[Eric Blake]

POSIX allows PATH_MAX to be undefined.  And even if you use the
gnulib pathmax module, where "pathmax.h" guarantees a definition,
the definition might not be constant or might be so large as to
be wasteful or cause stack overflows.  PATH_MAX should only be
used as a limit or hueristic, not an array size.

* top/maint.mk (sc_prohibit_path_max_array): New rule.

Signed-off-by: Eric Blake <address@hidden>
---

Within gnulib itself, there are some exceptions: lib/tmpname.c
and lib/stat.c use char[PATH_MAX] but only on mingw, where we
know the value is constant and small.  But this new rule helped
catch some violations in libvirt.

 ChangeLog    |    3 +++
 top/maint.mk |    9 +++++++++
 2 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index b4b82fa..9648603 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2011-06-22  Eric Blake  <address@hidden>

+       maint.mk: add syntax-check to avoid char[PATH_MAX]
+       * top/maint.mk (sc_prohibit_path_max_array): New rule.
+
        stat: be robust to PATH_MAX definition
        * lib/stat.c (rpl_stat): Require reasonable PATH_MAX.
        * modules/stat (Depends-on): Add verify.
diff --git a/top/maint.mk b/top/maint.mk
index 6f6b8be..4408a4e 100644
--- a/top/maint.mk
+++ b/top/maint.mk
@@ -1106,6 +1106,7 @@ sc_copyright_check:
 # the other init.sh-using tests also get it right.
 _hv_file ?= $(srcdir)/tests/help-version
 _hv_regex_weak ?= ^ *\. .*/init\.sh"
+# Fix syntax-highlighters "
 _hv_regex_strong ?= ^ *\. "\$${srcdir=\.}/init\.sh"
 sc_cross_check_PATH_usage_in_tests:
        @if test -f $(_hv_file); then                                   \
@@ -1133,6 +1134,14 @@ sc_Wundef_boolean:
        halt='Use 0 or 1 for macro values'                              \
          $(_sc_search_regexp)

+# Even if you use pathmax.h to guarantee that PATH_MAX is defined, it might
+# not be constant.  In general, use PATH_MAX as a limit, not an array
+# allocation bound.
+sc_prohibit_path_max_array:
+       @prohibit='\[PATH''_MAX'                                        \
+       halt='Avoid arrays of size PATH_MAX'                            \
+         $(_sc_search_regexp)
+
 sc_vulnerable_makefile_CVE-2009-4029:
        @prohibit='perm -777 -exec chmod a\+rwx|chmod 777 \$$\(distdir\)' \
        in_files=$$(find $(srcdir) -name Makefile.in)                   \
-- 
1.7.4.4