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From 087bd1bdff17025af6e5189898209035ec8d75da Mon Sep 17 00:00:00 2001
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From: Greg Hudson <ghudson@mit.edu>
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Date: Thu, 4 May 2017 17:03:35 -0400
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Subject: [PATCH] Add y2038 documentation
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ticket: 8352
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(cherry picked from commit 85d64c43dbf7a7faa56a1999494cdfa49e8bd2c9)
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---
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doc/appdev/index.rst | 1 +
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doc/appdev/y2038.rst | 28 ++++++++++++++++++++++++++++
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2 files changed, 29 insertions(+)
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create mode 100644 doc/appdev/y2038.rst
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diff --git a/doc/appdev/index.rst b/doc/appdev/index.rst
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index 3d62045ca..961bb1e9e 100644
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--- a/doc/appdev/index.rst
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+++ b/doc/appdev/index.rst
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@@ -5,6 +5,7 @@ For application developers
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:maxdepth: 1
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gssapi.rst
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+ y2038.rst
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h5l_mit_apidiff.rst
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init_creds.rst
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princ_handle.rst
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diff --git a/doc/appdev/y2038.rst b/doc/appdev/y2038.rst
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new file mode 100644
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index 000000000..bc4122dad
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--- /dev/null
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+++ b/doc/appdev/y2038.rst
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@@ -0,0 +1,28 @@
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+Year 2038 considerations for uses of krb5_timestamp
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+===================================================
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+
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+POSIX time values, which measure the number of seconds since January 1
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+1970, will exceed the maximum value representable in a signed 32-bit
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+integer in January 2038. This documentation describes considerations
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+for consumers of the MIT krb5 libraries.
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+
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+Applications or libraries which use libkrb5 and consume the timestamps
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+included in credentials or other structures make use of the
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+:c:type:`krb5_timestamp` type. For historical reasons, krb5_timestamp
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+is a signed 32-bit integer, even on platforms where a larger type is
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+natively used to represent time values. To behave properly for time
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+values after January 2038, calling code should cast krb5_timestamp
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+values to uint32_t, and then to time_t::
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+
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+ (time_t)(uint32_t)timestamp
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+
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+Used in this way, krb5_timestamp values can represent time values up
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+until February 2106, provided that the platform uses a 64-bit or
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+larger time_t type. This usage will also remain safe if a later
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+version of MIT krb5 changes krb5_timestamp to an unsigned 32-bit
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+integer.
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+
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+The GSSAPI only uses representations of time intervals, not absolute
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+times. Callers of the GSSAPI should require no changes to behave
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+correctly after January 2038, provided that they use MIT krb5 release
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+1.16 or later.
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