gnulib/regexec: Fix possible null-dereference

It appears to be possible that the mctx->state_log field may be NULL,
and the name of this function, clean_state_log_if_needed(), suggests
that it should be checking that it is valid to be cleaned before
assuming that it does.

Fixes: CID 86720

Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

bootstrap.conf

@@ -79,7 +79,8 @@ cp -a INSTALL INSTALL.grub
 
 bootstrap_post_import_hook () {
   set -e
-  for patchname in fix-base64 fix-null-deref fix-null-state-deref fix-uninit-structure fix-unused-value fix-width no-abort; do
+  for patchname in fix-base64 fix-null-deref fix-null-state-deref fix-regexec-null-deref \
+      fix-uninit-structure fix-unused-value fix-width no-abort; do
     patch -d grub-core/lib/gnulib -p2 \
       < "grub-core/lib/gnulib-patches/$patchname.patch"
   done

conf/Makefile.extra-dist

@@ -31,6 +31,7 @@ EXTRA_DIST += grub-core/genemuinitheader.sh
 EXTRA_DIST += grub-core/lib/gnulib-patches/fix-base64.patch
 EXTRA_DIST += grub-core/lib/gnulib-patches/fix-null-deref.patch
 EXTRA_DIST += grub-core/lib/gnulib-patches/fix-null-state-deref.patch
+EXTRA_DIST += grub-core/lib/gnulib-patches/fix-regexec-null-deref.patch
 EXTRA_DIST += grub-core/lib/gnulib-patches/fix-uninit-structure.patch
 EXTRA_DIST += grub-core/lib/gnulib-patches/fix-unused-value.patch
 EXTRA_DIST += grub-core/lib/gnulib-patches/fix-width.patch

grub-core/lib/gnulib-patches/fix-regexec-null-deref.patch

@@ -0,0 +1,12 @@
+--- a/lib/regexec.c	2020-10-21 14:25:35.310195912 +0000
++++ b/lib/regexec.c	2020-11-05 10:55:09.621542984 +0000
+@@ -1692,6 +1692,9 @@
+ {
+   Idx top = mctx->state_log_top;
+
++  if (mctx->state_log == NULL)
++    return REG_NOERROR;
++
+   if ((next_state_log_idx >= mctx->input.bufs_len
+        && mctx->input.bufs_len < mctx->input.len)
+       || (next_state_log_idx >= mctx->input.valid_len