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>

2 files changed, 9 insertions, 0 deletions

diff --git a/editors/awk.c b/editors/awk.c
index 079d0bde5..728ee8685 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -3128,6 +3128,9 @@ 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)
diff --git a/testsuite/awk.tests b/testsuite/awk.tests
index 93e25d8c1..bbf0fbff1 100755
--- a/testsuite/awk.tests
+++ b/testsuite/awk.tests
@@ -479,4 +479,10 @@ testing 'awk backslash+newline eaten with no trace' \
         "Hello world\n" \
         '' ''
 
+testing 'awk assign while test' \
+        "awk '\$1==\$1=\"foo\" {print \$1}'" \
+        "foo\n" \
+        "" \
+        "foo"
+
 exit $FAILCOUNT