[PATCH 3/3] dfa: avoid use of uninitialized constraint

[Paul Eggert]

* lib/dfa.c (merge_nfa_state): Do not initialize the constraint
to zero here.
(dfaoptimize): Do it here instead, via xcalloc.  This prevents the
use of an uninitialized constraint by later code when ! (flags[i]
& OPT_QUEUED) means merge_nfa_state was not called to initialize
the constraint.  Problem found by running 'valgrind src/grep -E
'(^| )*(a|b)*(c|d)*( |$)' < /dev/null' on Ubuntu 18.04.5 x86-64.
---
 ChangeLog | 9 +++++++++
 lib/dfa.c | 4 +---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 5f7a148e3..395ac6baf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2020-09-13  Paul Eggert  <eggert@cs.ucla.edu>
 
+       dfa: avoid use of uninitialized constraint
+       * lib/dfa.c (merge_nfa_state): Do not initialize the constraint
+       to zero here.
+       (dfaoptimize): Do it here instead, via xcalloc.  This prevents the
+       use of an uninitialized constraint by later code when ! (flags[i]
+       & OPT_QUEUED) means merge_nfa_state was not called to initialize
+       the constraint.  Problem found by running 'valgrind src/grep -E
+       '(^| )*(a|b)*(c|d)*( |$)' < /dev/null' on Ubuntu 18.04.5 x86-64.
+
        dfa: assume C99 in reorder_tokens
        * lib/dfa.c (reorder_tokens): Assume C99 and simplify.
 
diff --git a/lib/dfa.c b/lib/dfa.c
index 0fa9958fd..746c7b568 100644
--- a/lib/dfa.c
+++ b/lib/dfa.c
@@ -2428,8 +2428,6 @@ merge_nfa_state (struct dfa *d, idx_t tindex, char *flags,
   position_set *follows = d->follows;
   idx_t nelem = 0;
 
-  d->constraints[tindex] = 0;
-
   for (idx_t i = 0; i < follows[tindex].nelem; i++)
     {
       idx_t sindex = follows[tindex].elems[i].index;
@@ -2581,7 +2579,7 @@ dfaoptimize (struct dfa *d)
   position_set *merged = &merged0;
   alloc_position_set (merged, d->nleaves);
 
-  d->constraints = xnmalloc (d->tindex, sizeof *d->constraints);
+  d->constraints = xcalloc (d->tindex, sizeof *d->constraints);
 
   for (idx_t i = 0; i < d->tindex; i++)
     if (flags[i] & OPT_QUEUED)
-- 
2.17.1