busybox: awk: fix use after free (CVE-2022-30065)

This backports a commit which fixes a use after free bug in awk.

CVE-2022-30065 description:
A use-after-free in Busybox 1.35-x's awk applet leads to denial of
service and possibly code execution when processing a crafted awk
pattern in the copyvar function.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

package/utils/busybox/patches/001-CVE-2022-30065-awk-fix-use-after-free.patch

@@ -0,0 +1,42 @@
+From e63d7cdfdac78c6fd27e9e63150335767592b85e Mon Sep 17 00:00:00 2001
+From: Natanael Copa <ncopa@alpinelinux.org>
+Date: Fri, 17 Jun 2022 17:45:34 +0200
+Subject: awk: fix use after free (CVE-2022-30065)
+
+fixes https://bugs.busybox.net/show_bug.cgi?id=14781
+
+function                                             old     new   delta
+evaluate                                            3343    3357     +14
+
+Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
+Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
+---
+ editors/awk.c       | 3 +++
+ testsuite/awk.tests | 6 ++++++
+ 2 files changed, 9 insertions(+)
+
+--- a/editors/awk.c
++++ b/editors/awk.c
+@@ -3114,6 +3114,9 @@ static var *evaluate(node *op, var *res)
+ 
+ 		case XC( OC_MOVE ):
+ 			debug_printf_eval("MOVE\n");
++			/* make sure that we never return a temp var */
++			if (L.v == TMPVAR0)
++				L.v = res;
+ 			/* if source is a temporary string, jusk relink it to dest */
+ 			if (R.v == TMPVAR1
+ 			 && !(R.v->type & VF_NUMBER)
+--- a/testsuite/awk.tests
++++ b/testsuite/awk.tests
+@@ -469,4 +469,10 @@ testing 'awk printf %% prints one %' \
+ 	"%\n" \
+ 	'' ''
+ 
++testing 'awk assign while test' \
++	"awk '\$1==\$1=\"foo\" {print \$1}'" \
++	"foo\n" \
++	"" \
++	"foo"
++
+ exit $FAILCOUNT