Coverity has found a potential buffer overflow in the unicodedata module. The function call _getcode() which calls _cmpname(). _cmpname() copies data into fixed size buffer of length NAME_MAXLEN. Neither lookup() nor _getcode() limit name_length to NAME_MAXLEN. Therefore the buffer could theoretical overflow.

In practice the buffer overflow can't be abused because Tools/unicode/makeunicodedata.py already limits max name length. I still like to fix the bug because it is a low hanging fruit. In most versions of Python the code already checks that name_length fits in INT_MAX.

CID 1295028 (#1 of 1): Out-of-bounds access (OVERRUN)
overrun-call: Overrunning callee's array of size 256 by passing argument (int)name_length (which evaluates to 2147483647) in call to _getcode

For now the error message virtually always contains the name (unless the length of its UTF-8 representation > INT_MAX). With unicode_name_maxlen.patch it doesn't contains the name of length few hundreds or tens characters.

Proposed patch makes the error message always contain the name, but truncated to NAME_MAXLEN bytes.

>>> name = ''.join(map(chr, range(0x2c80, 0x2ce4)))
>>> unicodedata.lookup(name)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: "undefined character name 'ⲀⲁⲂⲃⲄⲅⲆⲇⲈⲉⲊⲋⲌⲍⲎⲏⲐⲑⲒⲓⲔⲕⲖⲗⲘⲙⲚⲛⲜⲝⲞⲟⲠⲡⲢⲣⲤⲥⲦⲧⲨⲩⲪⲫⲬⲭⲮⲯⲰⲱⲲⲳⲴⲵⲶⲷⲸⲹⲺⲻⲼⲽⲾⲿⳀⳁⳂⳃⳄⳅⳆⳇⳈⳉⳊⳋⳌⳍⳎⳏⳐⳑⳒⳓⳔ�...'"