avoid undeflow in regex poscache count

reginfo->poscache_iter is used to count down to zero; at zero, the
superlinear cache is enabled; and for values below zero the cache is
tested. After I32_MAX iterations the count might wrap to a positive value
on 32-bit systems. So don't do that.

1 files changed, 2 insertions, 0 deletions

diff --git a/regexec.c b/regexec.c
index d29f6dd8f4..12548d5d21 100644
--- a/regexec.c
+++ b/regexec.c
@@ -5475,6 +5475,8 @@ NULL
 		if (reginfo->poscache_iter < 0) {
 		    /* have we already failed at this position? */
 		    I32 offset, mask;
+
+                    reginfo->poscache_iter = -1; /* stop eventual underflow */
 		    offset  = (scan->flags & 0xf) - 1
                                 +   (locinput - reginfo->strbeg)
                                   * (scan->flags>>4);