Efficient Substr implementation

I came up with this implementation of substring method. Anyone got ideas to make it more terse and more efficient?

bool substring(const char* str, const char* substr){
  const char *currentString = str, *backTrackString = str, *currSubstr = substr;
  while( strlen(backTrackString) >= strlen(substr) ){
    while( *currSubstr && *currentString++ == *currSubstr++);
    if( !*currSubstr ) return true;
    currentString = backTrackString++;
    currSubstr = substr;
  }
  return false;
}

In particular, can we do without atleast one of the local variables - while still being as efficient or better? A more basic question - so you think this is efficient?

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