diff Misc/python.man @ 75100:6b7704fe1be1 2.6

- Issue #13703: oCERT-2011-003: add -R command-line option and PYTHONHASHSEED environment variable, to provide an opt-in way to protect against denial of service attacks due to hash collisions within the dict and set types. Patch by David Malcolm, based on work by Victor Stinner.
author Barry Warsaw <barry@python.org>
date Mon, 20 Feb 2012 20:42:21 -0500
parents 6e6b59413a13
children 65d1fe86618f a0f43f4481e0
line wrap: on
line diff
--- a/Misc/python.man	Mon Feb 20 14:43:22 2012 -0500
+++ b/Misc/python.man	Mon Feb 20 20:42:21 2012 -0500
@@ -34,6 +34,9 @@
 .B \-O0
 ]
 [
+.B \-R
+]
+[
 .B -Q
 .I argument
 ]
@@ -151,6 +154,18 @@
 .B \-O0
 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
@@ -411,6 +426,20 @@
 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