dfa: avoid invalid match or infinite loop in unused matching mode

Neither grep nor gawk uses this DFA code in its matching mode,
since each always calls dfacomp with a nonzero final argument.
However, when used in that mode, it had bug:
After failing to match in matching mode, it should return NULL,
but instead would either report a false match or enter an
infinite loop.

* src/dfa.c (dfaexec_main): After failing to match in matching mode
return NULL, rather than transitioning to the next state.
* tests/dfa-match: Add a new test.
* tests/dfa-match-aux.c: Add a new program to exercise this
otherwise-unused part of dfa.c.
* tests/Makefile.am: Add a rule to build new test.
(check_PROGRAMS): Add dfa-match-aux.
(AM_CPPFLAGS): Add -I$(top_srcdir)/src.
(TESTS): Add dfa-match.
* cfg.mk (exclude_file_name_regexp--sc_bindtextdomain):
(exclude_file_name_regexp--sc_prohibit_atoi_atof):
Exempt the new test file from some syntax-check rules.

1 files changed, 5 insertions, 1 deletions

diff --git a/cfg.mk b/cfg.mk
index 554335ad..3093ba3c 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -118,7 +118,11 @@ update-copyright-env = \
   UPDATE_COPYRIGHT_USE_INTERVALS=1 \
   UPDATE_COPYRIGHT_MAX_LINE_LENGTH=79
 
-exclude_file_name_regexp--sc_bindtextdomain = ^tests/get-mb-cur-max\.c$$
+exclude_file_name_regexp--sc_bindtextdomain = \
+  ^tests/(get-mb-cur-max|dfa-match-aux)\.c$$
+exclude_file_name_regexp--sc_prohibit_atoi_atof = \
+  ^tests/dfa-match-aux\.c$$
+
 exclude_file_name_regexp--sc_prohibit_strcmp = /colorize-.*\.c$$
 exclude_file_name_regexp--sc_prohibit_xalloc_without_use = ^src/kwset\.c$$
 exclude_file_name_regexp--sc_prohibit_tab_based_indentation = \