extmod/re1.5: Check and report byte overflow errors in _compilecode.

The generated regex code is limited in the range of jumps and counts, and
this commit checks all cases which can overflow given the right kind of
input regex, and returns an error in such a case.

This change assumes that the results that overflow an int8_t do not
overflow a platform int.

Closes: #7078
Signed-off-by: Jeff Epler <jepler@gmail.com>

extmod/re1.5/compilecode.c

@@ -8,11 +8,20 @@
     ((code ? memmove(code + at + num, code + at, pc - at) : 0), pc += num)
 #define REL(at, to) (to - at - 2)
 #define EMIT(at, byte) (code ? (code[at] = byte) : (at))
+#define EMIT_CHECKED(at, byte) (_emit_checked(at, code, byte, &err))
 #define PC (prog->bytelen)
 
+static void _emit_checked(int at, char *code, int val, bool *err) {
+    *err |= val != (int8_t)val;
+    if (code) {
+        code[at] = val;
+    }
+}
+
 static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
 {
     char *code = sizecode ? NULL : prog->insts;
+    bool err = false;
     int start = PC;
     int term = PC;
     int alt_label = 0;
@@ -64,7 +73,7 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
                 }
                 EMIT(PC++, *re);
             }
-            EMIT(term + 1, cnt);
+            EMIT_CHECKED(term + 1, cnt);
             break;
         }
         case '(': {
@@ -75,7 +84,7 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
             if (capture) {
                 sub = ++prog->sub;
                 EMIT(PC++, Save);
-                EMIT(PC++, 2 * sub);
+                EMIT_CHECKED(PC++, 2 * sub);
                 prog->len++;
             } else {
                     re += 2;
@@ -86,7 +95,7 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
 
             if (capture) {
                 EMIT(PC++, Save);
-                EMIT(PC++, 2 * sub + 1);
+                EMIT_CHECKED(PC++, 2 * sub + 1);
                 prog->len++;
             }
 
@@ -101,7 +110,7 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
             } else {
                 EMIT(term, Split);
             }
-            EMIT(term + 1, REL(term, PC));
+            EMIT_CHECKED(term + 1, REL(term, PC));
             prog->len++;
             term = PC;
             break;
@@ -109,7 +118,7 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
             if (PC == term) return NULL; // nothing to repeat
             INSERT_CODE(term, 2, PC);
             EMIT(PC, Jmp);
-            EMIT(PC + 1, REL(PC, term));
+            EMIT_CHECKED(PC + 1, REL(PC, term));
             PC += 2;
             if (re[1] == '?') {
                 EMIT(term, RSplit);
@@ -117,7 +126,7 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
             } else {
                 EMIT(term, Split);
             }
-            EMIT(term + 1, REL(term, PC));
+            EMIT_CHECKED(term + 1, REL(term, PC));
             prog->len += 2;
             term = PC;
             break;
@@ -129,20 +138,20 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
             } else {
                 EMIT(PC, RSplit);
             }
-            EMIT(PC + 1, REL(PC, term));
+            EMIT_CHECKED(PC + 1, REL(PC, term));
             PC += 2;
             prog->len++;
             term = PC;
             break;
         case '|':
             if (alt_label) {
-                EMIT(alt_label, REL(alt_label, PC) + 1);
+                EMIT_CHECKED(alt_label, REL(alt_label, PC) + 1);
             }
             INSERT_CODE(start, 2, PC);
             EMIT(PC++, Jmp);
             alt_label = PC++;
             EMIT(start, Split);
-            EMIT(start + 1, REL(start, PC));
+            EMIT_CHECKED(start + 1, REL(start, PC));
             prog->len += 2;
             term = PC;
             break;
@@ -160,9 +169,9 @@ static const char *_compilecode(const char *re, ByteProg *prog, int sizecode)
     }
 
     if (alt_label) {
-        EMIT(alt_label, REL(alt_label, PC) + 1);
+        EMIT_CHECKED(alt_label, REL(alt_label, PC) + 1);
     }
-    return re;
+    return err ? NULL : re;
 }
 
 int re1_5_sizecode(const char *re)

tests/extmod/ure_limit.py

+# Test overflow in ure.compile output code.
+
+try:
+    import ure as re
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+
+def test_re(r):
+    try:
+        re.compile(r)
+    except:
+        print("Error")
+
+
+# too many chars in []
+test_re("[" + "a" * 256 + "]")
+
+# too many groups
+test_re("(a)" * 256)
+
+# jump too big for ?
+test_re("(" + "a" * 62 + ")?")
+
+# jump too big for *
+test_re("(" + "a" * 60 + ".)*")
+test_re("(" + "a" * 60 + "..)*")
+
+# jump too big for +
+test_re("(" + "a" * 62 + ")+")
+
+# jump too big for |
+test_re("b" * 63 + "|a")

tests/extmod/ure_limit.py.exp

+Error
+Error
+Error
+Error
+Error
+Error
+Error