From 9ddda243d7d4fba4beb1868f6285f51369f6ceda Mon Sep 17 00:00:00 2001
From: Jeff Genovy <29107334+jefgen@users.noreply.github.com>
Date: Mon, 9 Aug 2021 18:37:22 -0700
Subject: [PATCH] ICU-21705 ICU-21706 Fix crash if ICU's default locale has
 BCP47 Unicode Extensions, and fix ures_openDirect crash with NULL locale ID.

Add test case for ures_openDirect with NULL locale ID.
---
 icu4c/source/common/uresbund.cpp     | 26 +++++++++++++++++++-------
 icu4c/source/test/cintltst/crestst.c |  8 +++++++-
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/icu4c/source/common/uresbund.cpp b/icu4c/source/common/uresbund.cpp
index 18f474ea5fa..4ca3a348910 100644
--- a/icu4c/source/common/uresbund.cpp
+++ b/icu4c/source/common/uresbund.cpp
@@ -461,11 +461,10 @@ getPoolEntry(const char *path, UErrorCode *status) {
 /* INTERNAL: */
 /*   CAUTION:  resbMutex must be locked when calling this function! */
 static UResourceDataEntry *
-findFirstExisting(const char* path, char* name,
+findFirstExisting(const char* path, char* name, const char* defaultLocale,
                   UBool *isRoot, UBool *hasChopped, UBool *isDefault, UErrorCode* status) {
     UResourceDataEntry *r = NULL;
     UBool hasRealData = FALSE;
-    const char *defaultLoc = uloc_getDefault();
     *hasChopped = TRUE; /* we're starting with a fresh name */
 
     while(*hasChopped && !hasRealData) {
@@ -474,7 +473,7 @@ findFirstExisting(const char* path, char* name,
         if (U_FAILURE(*status)) {
             return NULL;
         }
-        *isDefault = (UBool)(uprv_strncmp(name, defaultLoc, uprv_strlen(name)) == 0);
+        *isDefault = (UBool)(uprv_strncmp(name, defaultLocale, uprv_strlen(name)) == 0);
         hasRealData = (UBool)(r->fBogus == U_ZERO_ERROR);
         if(!hasRealData) {
             /* this entry is not real. We will discard it. */
@@ -669,10 +668,13 @@ static UResourceDataEntry *entryOpen(const char* path, const char* localeID,
         }
     }
  
+    // Note: We need to query the default locale *before* locking resbMutex.
+    const char *defaultLocale = uloc_getDefault();
+
     Mutex lock(&resbMutex);    // Lock resbMutex until the end of this function.
 
     /* We're going to skip all the locales that do not have any data */
-    r = findFirstExisting(path, name, &isRoot, &hasChopped, &isDefault, &intStatus);
+    r = findFirstExisting(path, name, defaultLocale, &isRoot, &hasChopped, &isDefault, &intStatus);
 
     // If we failed due to out-of-memory, report the failure and exit early.
     if (intStatus == U_MEMORY_ALLOCATION_ERROR) {
@@ -712,8 +714,8 @@ static UResourceDataEntry *entryOpen(const char* path, const char* localeID,
     /* if that is the case, we need to chain in the default locale   */
     if(r==NULL && openType == URES_OPEN_LOCALE_DEFAULT_ROOT && !isDefault && !isRoot) {
         /* insert default locale */
-        uprv_strcpy(name, uloc_getDefault());
-        r = findFirstExisting(path, name, &isRoot, &hasChopped, &isDefault, &intStatus);
+        uprv_strcpy(name, defaultLocale);
+        r = findFirstExisting(path, name, defaultLocale, &isRoot, &hasChopped, &isDefault, &intStatus);
         // If we failed due to out-of-memory, report the failure and exit early.
         if (intStatus == U_MEMORY_ALLOCATION_ERROR) {
             *status = intStatus;
@@ -737,7 +739,7 @@ static UResourceDataEntry *entryOpen(const char* path, const char* localeID,
     /* present */
     if(r == NULL) {
         uprv_strcpy(name, kRootLocaleName);
-        r = findFirstExisting(path, name, &isRoot, &hasChopped, &isDefault, &intStatus);
+        r = findFirstExisting(path, name, defaultLocale, &isRoot, &hasChopped, &isDefault, &intStatus);
         // If we failed due to out-of-memory, report the failure and exit early.
         if (intStatus == U_MEMORY_ALLOCATION_ERROR) {
             *status = intStatus;
@@ -791,7 +793,17 @@ entryOpenDirect(const char* path, const char* localeID, UErrorCode* status) {
         return NULL;
     }
 
+    // Note: We need to query the default locale *before* locking resbMutex.
+    // If the localeID is NULL, then we want to use the default locale.
+    if (localeID == NULL) {
+        localeID = uloc_getDefault();
+    } else if (*localeID == 0) {
+        // If the localeID is "", then we want to use the root locale.
+        localeID = kRootLocaleName;
+    }
+
     Mutex lock(&resbMutex);
+
     // findFirstExisting() without fallbacks.
     UResourceDataEntry *r = init_entry(localeID, path, status);
     if(U_SUCCESS(*status)) {
diff --git a/icu4c/source/test/cintltst/crestst.c b/icu4c/source/test/cintltst/crestst.c
index 080301090d1..d79ff8f1e50 100644
--- a/icu4c/source/test/cintltst/crestst.c
+++ b/icu4c/source/test/cintltst/crestst.c
@@ -496,7 +496,7 @@ static void TestFallback()
 
 static void
 TestOpenDirect(void) {
-    UResourceBundle *idna_rules, *casing, *te_IN, *ne, *item;
+    UResourceBundle *idna_rules, *casing, *te_IN, *ne, *item, *defaultLocale;
     UErrorCode errorCode;
 
     /*
@@ -641,6 +641,12 @@ TestOpenDirect(void) {
         ures_close(item);
     }
     ures_close(te_IN);
+
+    // ICU-21705
+    // Verify that calling ures_openDirect() with a NULL localeID doesn't crash or assert.
+    errorCode = U_ZERO_ERROR;
+    defaultLocale = ures_openDirect(NULL, NULL, &errorCode);
+    ures_close(defaultLocale);
 }
 
 static void