Mercurial > cpython-lru_cache-weakref
diff Misc/python.man @ 75066:f4b7ecf8a5f8 3.1
Issue #13703: add a way to randomize the hash values of basic types (str, bytes, datetime)
in order to make algorithmic complexity attacks on (e.g.) web apps much more complicated.
The environment variable PYTHONHASHSEED and the new command line flag -R control this
behavior.
| author | Georg Brandl <georg@python.org> |
|---|---|
| date | Mon, 20 Feb 2012 19:54:16 +0100 |
| parents | c57fdce01eb8 |
| children | 358aee0a9ad5 4a31f6b11e7a |
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--- a/Misc/python.man Sat Feb 18 14:42:57 2012 +0100 +++ b/Misc/python.man Mon Feb 20 19:54:16 2012 +0100 @@ -34,6 +34,9 @@ .B \-OO ] [ +.B \-R +] +[ .B -Q .I argument ] @@ -145,6 +148,18 @@ .B \-OO Discard docstrings in addition to the \fB-O\fP optimizations. .TP +.B \-R +Turn on "hash randomization", so that the hash() values of str, bytes and +datetime objects are "salted" with an unpredictable pseudo-random value. +Although they remain constant within an individual Python process, they are +not predictable between repeated invocations of Python. +.IP +This is intended to provide protection against a denial of service +caused by carefully-chosen inputs that exploit the worst case performance +of a dict insertion, O(n^2) complexity. See +http://www.ocert.org/advisories/ocert-2011-003.html +for details. +.TP .BI "\-Q " argument Division control; see PEP 238. The argument must be one of "old" (the default, int/int and long/long return an int or long), "new" (new @@ -403,6 +418,20 @@ If this is set to a non-empty string it is equivalent to specifying the \fB\-v\fP option. If set to an integer, it is equivalent to specifying \fB\-v\fP multiple times. +.IP PYTHONHASHSEED +If this variable is set to "random", the effect is the same as specifying +the \fB-R\fP option: a random value is used to seed the hashes of str, +bytes and datetime objects. + +If PYTHONHASHSEED is set to an integer value, it is used as a fixed seed for +generating the hash() of the types covered by the hash randomization. Its +purpose is to allow repeatable hashing, such as for selftests for the +interpreter itself, or to allow a cluster of python processes to share hash +values. + +The integer must be a decimal number in the range [0,4294967295]. Specifying +the value 0 will lead to the same hash values as when hash randomization is +disabled. .SH AUTHOR The Python Software Foundation: http://www.python.org/psf .SH INTERNET RESOURCES
