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Fix: heap-use-after-free in merge_patch when patch is subtree of target #1065

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Fix: heap-use-after-free in merge_patch when patch is subtree of target #1065

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8 changes: 6 additions & 2 deletions cJSON_Utils.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1324,9 +1324,13 @@ static cJSON *merge_patch(cJSON *target, const cJSON * const patch, const cJSON_

if (!cJSON_IsObject(patch))
{
/* scalar value, array or NULL, just duplicate */
/* scalar value, array or NULL, just duplicate.
* Duplicate the patch first in case it is a subtree of target,
* otherwise cJSON_Delete(target) would free the patch memory
* and the subsequent cJSON_Duplicate would read freed memory. */
cJSON *duplicate = cJSON_Duplicate(patch, 1);
cJSON_Delete(target);
return cJSON_Duplicate(patch, 1);
return duplicate;
}

if (!cJSON_IsObject(target))
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34 changes: 34 additions & 0 deletions tests/old_utils_tests.c
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Original file line number Diff line number Diff line change
Expand Up @@ -189,6 +189,39 @@ static void merge_tests(void)
}
}

static void merge_patch_should_not_read_freed_memory_when_patch_is_subtree(void)
{
/* When patch is a subtree of target, merge_patch must duplicate the patch
* before deleting target. Otherwise cJSON_Delete(target) frees the patch
* memory and the subsequent cJSON_Duplicate reads freed memory (UAF).
* See CVE candidate: heap-use-after-free in merge_patch (cJSON_Utils.c). */
cJSON *target = cJSON_Parse("{\"a\":[1,2,3]}");
cJSON *patch = cJSON_GetObjectItem(target, "a");
cJSON *result = NULL;
cJSON *first = NULL;
cJSON *second = NULL;
cJSON *third = NULL;

TEST_ASSERT_NOT_NULL(target);
TEST_ASSERT_NOT_NULL(patch);

/* patch (array [1,2,3]) is a subtree of target. This used to trigger
* heap-use-after-free under AddressSanitizer before the fix. */
result = cJSONUtils_MergePatch(target, patch);
TEST_ASSERT_NOT_NULL(result);
TEST_ASSERT_TRUE(cJSON_IsArray(result));
TEST_ASSERT_EQUAL_INT(3, cJSON_GetArraySize(result));

first = cJSON_GetArrayItem(result, 0);
second = cJSON_GetArrayItem(result, 1);
third = cJSON_GetArrayItem(result, 2);
TEST_ASSERT_EQUAL_INT(1, first->valueint);
TEST_ASSERT_EQUAL_INT(2, second->valueint);
TEST_ASSERT_EQUAL_INT(3, third->valueint);

cJSON_Delete(result);
}

static void generate_merge_tests(void)
{
size_t i = 0;
Expand Down Expand Up @@ -219,6 +252,7 @@ int main(void)
RUN_TEST(misc_tests);
RUN_TEST(sort_tests);
RUN_TEST(merge_tests);
RUN_TEST(merge_patch_should_not_read_freed_memory_when_patch_is_subtree);
RUN_TEST(generate_merge_tests);

return UNITY_END();
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