[C++][Gandiva] Out-of-bounds read in mask functions from wrong utf8proc_iterate length #50707

The Gandiva mask stubs walk a utf8 string with utf8proc_iterate, but pass the total data_len as the remaining-byte count instead of data_len - bytes_read even though the pointer has already advanced:

• gdv_mask_first_n_utf8_int32
• gdv_mask_last_n_utf8_int32
• mask_utf8_utf8_utf8_utf8

utf8proc_iterate(str, strlen, ...) reads up to strlen bytes from str. With str = data + bytes_read and strlen = data_len, a truncated trailing multi-byte glyph (for example a lead byte 0xF0 as the final byte of an exactly-sized value buffer) makes utf8proc read continuation bytes past data + data_len.

This is reachable from mask() / mask_first_n() / mask_last_n() on untrusted string data whose value buffer is exactly sized. Passing the true remaining length lets utf8proc report the truncated glyph instead of over-reading.

Component(s)

C++, Gandiva