preproc.: Fix NULL dereference on broken %strlen argument

Under particular circumstances %strlen may cause SIGSEG. A typical
example is %strlen with nonexistent macro argument.

[ Testcase test/strlen.asm ]

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

2 files changed, 6 insertions, 1 deletions

diff --git a/preproc.c b/preproc.c
index 7fc3e74d..d75b58eb 100644
--- a/preproc.c
+++ b/preproc.c
@@ -3254,7 +3254,7 @@ issue_error:
         while (tok_type_(t, TOK_WHITESPACE))
             t = t->next;
         /* t should now point to the string */
-        if (t->type != TOK_STRING) {
+        if (!tok_type_(t, TOK_STRING)) {
             error(ERR_NONFATAL,
                   "`%%strlen` requires string as second parameter");
             free_tlist(tline);
diff --git a/test/strlen.asm b/test/strlen.asm
new file mode 100644
index 00000000..913014ce
--- /dev/null
+++ b/test/strlen.asm
@@ -0,0 +1,5 @@
+%macro strlen_test 1
+    %strlen len %2 ; not existing argument
+%endmacro
+
+strlen_test 'a'