ICU-22555 Fix infinity loop in RuleBasedCollator constructor

Fix C++ and Java code.
Add unit tests for both C++ and Java.

icu4c/source/common/caniter.cpp

@@ -264,10 +264,19 @@ void CanonicalIterator::setSource(const UnicodeString &newSource, UErrorCode &st
  * @param source the string to find permutations for
  * @return the results in a set.
  */
-void U_EXPORT2 CanonicalIterator::permute(UnicodeString &source, UBool skipZeros, Hashtable *result, UErrorCode &status) {
+void U_EXPORT2 CanonicalIterator::permute(UnicodeString &source, UBool skipZeros, Hashtable *result, UErrorCode &status, int32_t depth) {
     if(U_FAILURE(status)) {
         return;
     }
+    // To avoid infinity loop caused by permute, we limit the depth of recursive
+    // call to permute and return U_UNSUPPORTED_ERROR.
+    // We know in some unit test we need at least 4. Set to 8 just in case some
+    // unforseen use cases.
+    constexpr int32_t kPermuteDepthLimit = 8;
+    if (depth > kPermuteDepthLimit) {
+        status = U_UNSUPPORTED_ERROR;
+        return;
+    }
     //if (PROGRESS) printf("Permute: %s\n", UToS(Tr(source)));
     int32_t i = 0;
 
@@ -311,7 +320,7 @@ void U_EXPORT2 CanonicalIterator::permute(UnicodeString &source, UBool skipZeros
 
         // see what the permutations of the characters before and after this one are
         //Hashtable *subpermute = permute(source.substring(0,i) + source.substring(i + UTF16.getCharCount(cp)));
-        permute(subPermuteString.remove(i, U16_LENGTH(cp)), skipZeros, &subpermute, status);
+        permute(subPermuteString.remove(i, U16_LENGTH(cp)), skipZeros, &subpermute, status, depth+1);
         /* Test for buffer overflows */
         if(U_FAILURE(status)) {
             return;

icu4c/source/common/unicode/caniter.h

@@ -128,9 +128,10 @@ class U_COMMON_API CanonicalIterator final : public UObject {
      * @param skipZeros  determine if skip zeros
      * @param result     the results in a set.
      * @param status       Fill-in parameter which receives the status of this operation.
+     * @param depth     depth of the call.
      * @internal
      */
-    static void U_EXPORT2 permute(UnicodeString &source, UBool skipZeros, Hashtable *result, UErrorCode &status);
+    static void U_EXPORT2 permute(UnicodeString &source, UBool skipZeros, Hashtable *result, UErrorCode &status, int32_t depth=0);
 #endif  /* U_HIDE_INTERNAL_API */
 
     /**

icu4c/source/test/intltest/regcoll.cpp

@@ -1249,6 +1249,25 @@ void CollationRegressionTest::TestBeforeWithTooStrongAfter() {
     }
 }
 
+void CollationRegressionTest::TestICU22555InfinityLoop() {
+    char16_t data[] = {
+        0x0020, 0x0026, 0x4000, 0x002c, 0x6601, 0x0106, 0xff7f, 0xff99,
+        0x003b, 0x1141, 0x106a, 0x1006, 0x0001, 0x0080, 0x1141, 0x106a,
+        0x0026, 0x00ff, 0xff6f, 0xff99, 0x013b, 0x1141, 0x1067, 0x1026,
+        0x0601, 0x0080, 0x5f03, 0x17e3, 0x0000, 0x3e00, 0x3e3e, 0x0055,
+        0x8080, 0x0000, 0x01e4, 0x0000, 0x0300, 0x003d, 0x4cff, 0x8053,
+        0x7a65, 0x0000, 0x6400, 0x5f00, 0x0150, 0x9090, 0x9090, 0x2f5f,
+        0x0053, 0xffe4, 0x002c, 0x0300, 0x1f3d, 0x55f7, 0x8053, 0x1750,
+        0x3d00, 0xff00, 0x00ff, 0xff6f, 0x0099, 0x03fa, 0x0303, 0x0303,
+        0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303,
+        0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303,
+    };
+    icu::UnicodeString rule(false, data, sizeof(data)/sizeof(char16_t));
+    UErrorCode status = U_ZERO_ERROR;
+    icu::LocalPointer<icu::RuleBasedCollator> col1(
+        new icu::RuleBasedCollator(rule, status));
+}
+
 void CollationRegressionTest::TestICU22517() {
     IcuTestErrorCode errorCode(*this, "TestICU22517");
     char16_t data[] = u"&a=b쫊쫊쫊쫊쫊쫊쫊쫊";
@@ -1421,6 +1440,7 @@ void CollationRegressionTest::runIndexedTest(int32_t index, UBool exec, const ch
     TESTCASE_AUTO(TestBeforeWithTooStrongAfter);
     TESTCASE_AUTO(TestICU22277);
     TESTCASE_AUTO(TestICU22517);
+    TESTCASE_AUTO(TestICU22555InfinityLoop);
     TESTCASE_AUTO_END;
 }
 

icu4c/source/test/intltest/regcoll.h

@@ -242,6 +242,8 @@ class CollationRegressionTest: public IntlTestCollator
 
     void TestICU22517();
 
+    void TestICU22555InfinityLoop();
+
 private:
     //------------------------------------------------------------------------
     // Internal utilities

icu4j/main/collate/src/test/java/com/ibm/icu/dev/test/collator/CollationRegressionTest.java

@@ -1243,6 +1243,27 @@ public void TestICU22517() {
         }
     }
 
+    @Test
+    public void TestICU22555InfinityLoop() {
+        char data[] = {
+            0x0020, 0x0026, 0x4000, 0x002c, 0x6601, 0x0106, 0xff7f, 0xff99,
+            0x003b, 0x1141, 0x106a, 0x1006, 0x0001, 0x0080, 0x1141, 0x106a,
+            0x0026, 0x00ff, 0xff6f, 0xff99, 0x013b, 0x1141, 0x1067, 0x1026,
+            0x0601, 0x0080, 0x5f03, 0x17e3, 0x0000, 0x3e00, 0x3e3e, 0x0055,
+            0x8080, 0x0000, 0x01e4, 0x0000, 0x0300, 0x003d, 0x4cff, 0x8053,
+            0x7a65, 0x0000, 0x6400, 0x5f00, 0x0150, 0x9090, 0x9090, 0x2f5f,
+            0x0053, 0xffe4, 0x002c, 0x0300, 0x1f3d, 0x55f7, 0x8053, 0x1750,
+            0x3d00, 0xff00, 0x00ff, 0xff6f, 0x0099, 0x03fa, 0x0303, 0x0303,
+            0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303,
+            0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303, 0x0303,
+        };
+        String rule = new String(data, 0, data.length);
+        try {
+            RuleBasedCollator coll = new RuleBasedCollator(rule);
+        } catch(Exception expected) {
+        }
+    }
+
     @Test
     public void TestBeforeWithTooStrongAfter() {
         // ICU ticket #9959:

icu4j/main/core/src/main/java/com/ibm/icu/text/CanonicalIterator.java

@@ -154,6 +154,10 @@ public void setSource(String newSource) {
         }
     }
 
+    // To avoid infinity loop caused by permute, we limit the depth of recursive
+    // call to permute and throw exception.
+    // We know in some unit test we need at least 4. Set to 8 just in case some
+    // unforseen use cases.
     /**
      * Simple implementation of permutation.
      * <br><b>Warning: The strings are not guaranteed to be in any particular order.</b>
@@ -165,9 +169,27 @@ public void setSource(String newSource) {
      */
     @Deprecated
     public static void permute(String source, boolean skipZeros, Set<String> output) {
+        permute(source, skipZeros, output, 0);
+    }
+
+    private static int PERMUTE_DEPTH_LIMIT = 8;
+    /**
+     * Simple implementation of permutation.
+     * <br><b>Warning: The strings are not guaranteed to be in any particular order.</b>
+     * @param source the string to find permutations for
+     * @param skipZeros set to true to skip characters with canonical combining class zero
+     * @param output the set to add the results to
+     * @param depth the depth of the recursive call.
+     * @internal
+     * @deprecated This API is ICU internal only.
+     */
+    @Deprecated
+    private static void permute(String source, boolean skipZeros, Set<String> output, int depth) {
         // TODO: optimize
         //if (PROGRESS) System.out.println("Permute: " + source);
-
+        if (depth > PERMUTE_DEPTH_LIMIT) {
+            throw new UnsupportedOperationException("Stack too deep:" + depth);
+        }
         // optimization:
         // if zero or one character, just return a set with it
         // we check for length < 2 to keep from counting code points all the time
@@ -193,7 +215,7 @@ public static void permute(String source, boolean skipZeros, Set<String> output)
             // see what the permutations of the characters before and after this one are
             subpermute.clear();
             permute(source.substring(0,i)
-                + source.substring(i + UTF16.getCharCount(cp)), skipZeros, subpermute);
+                + source.substring(i + UTF16.getCharCount(cp)), skipZeros, subpermute, depth+1);
 
             // prefix this character to all of them
             String chStr = UTF16.valueOf(source, i);