lib/re1.5: Check stack during compilecode.

Otherwise, a very deeply nested regular expression like

    re.compile("(" * 65536)

can exhaust the host stack during the compile phase. This turns
that into a `RuntimeError: maximum recursion depth exceeded`
instead.

This crash was found via fuzzing.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>

lib/re1.5/compilecode.c

@@ -29,6 +29,8 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
     int term = PC;
     int alt_label = 0;
 
+    re1_5_stack_chk();
+
     for (; *re && *re != ')'; re++) {
         switch (*re) {
         case '\\':

tests/extmod/re_stack_overflow2.py

@@ -0,0 +1,25 @@
+# Test overflow in re.compile output code.
+
+try:
+    import re
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+
+def test_re(r):
+    try:
+        re.compile(r)
+    except:
+        print("Error")
+
+
+try:
+    r = "(" * 65536 + ")" * 65536
+except MemoryError:
+    print("SKIP")
+    raise SystemExit
+
+# This happens to trigger RecursionError on current versions of CPython
+# (tested with 3.13.5) as well, so no .exp file is needed.
+test_re(r)

tests/run-tests.py

@@ -178,6 +178,7 @@ platform_tests_to_skip = {
         "extmod/binascii_a2b_base64.py",
         "extmod/deflate_compress_memory_error.py",  # tries to allocate unlimited memory
         "extmod/re_stack_overflow.py",
+        "extmod/re_stack_overflow2.py",
         "extmod/time_res.py",
         "extmod/vfs_posix.py",
         "extmod/vfs_posix_enoent.py",