AES128 memcry() crash

Question

- (NSData *)kd_AES128EncryptWithKey:(NSString *)key {
    if (key.length == 0) {
        return nil;
    }
    char keyPtr[kCCKeySizeAES128 + 1];

    memset(keyPtr, 0, sizeof(keyPtr));
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

    NSUInteger dataLength = [self length];
    int diff = kCCKeySizeAES128 - (dataLength % kCCKeySizeAES128);
    NSUInteger newSize = 0;

    if (diff > 0) {
        newSize = dataLength + diff;
    }

    char dataPtr[newSize];
    memcpy(dataPtr, [self bytes], [self length]); // crash  EXC_BAD_ACCESS

    ...
    free(buffer);
    return nil;
}

in this crash: newSize = 800016 dataSize = 800001

When i make AES128 encrypt for NSData(800001 bytes), crash in memcry(), but if the data is smaller , it work normal

Could someone help me?

Answer 1

your dataPtr is allocated in the stack which always has a certain limit. If you are dealing with big chunks of memory, then use heap instead:

char *dataPtr = (char *)malloc(newSize);

and don't forget to free it later

Answer 2

If diff <= 0 newSize is 0 so no memory will be aqllocated to dataPtr : char dataPtr[newSize]; so the memcpy will crash.