Root Cause Analysis: Looking at the given vulnerable code line and its context, the CWE-787 vulnerability (out-of-bounds write) exists because it is possible for `fl->num_fh` to be negative, which could lead to a heap buffer overflow if it is used to allocate memory for `fl->fh_array`. This can happen if the `be32_to_cpup` function returns an invalid value for `fl->num_fh`. In this case, allocating memory for `fl->fh_array` with `fl->num_fh * sizeof(nfs_fh *)` can lead to a heap buffer overflow vulnerability, which is CWE-787.