On 09/30/2014 02:41 PM, Nathaniel McCallum wrote:
On Tue, 2014-09-30 at 13:42 +0200, thierry bordaz wrote:
On 09/29/2014 08:38 PM, Nathaniel McCallum wrote:
On Thu, 2014-09-25 at 15:15 +0200, thierry bordaz wrote:
On 09/19/2014 07:53 PM, Nathaniel McCallum wrote:
This prevents synchronization when an authentication collision occurs.
https://fedorahosted.org/freeipa/ticket/4493
NOTE: this patch is related to the above ticket, but does not solve it.
For the solution, please see patch 0064. This behavior fix is from patch
0062 (rescinded) and is worth keeping.
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Hello Nathaniel,
.
My understanding is that during a pre_bind, the plugins
validates token codes (for example "HOTP") checking that step
ranges [-25..+25].
As soon as the token is valid, the new HOTPcounter is written
in the entry.
But in case of negative steps,I believe the otp-decrement
plugin will reject this update.
HOTP never goes backwards. See line 188 in libotp.c. Even if this check
weren't present, we would *want* the decrement plugin to reject the
update.
Ok.
If TOTPwatermark is updated and there is a second token code,
then clockOffset is also updated.
This update is done during a pre_bind, so if there are
parallel binds on the server, there is a possibility that
TOTPwatermark is updated from a bind and 'clockOffset' updated
from an other bind.
An option is to do a single internal modify to update both.
We don't care about atomicity in this case. If two TOTP synchronizations
occur at almost the same time, the value of clockOffset will be written
twice with the same value. Since the values are the same, we don't care
which value gets written first.
I was just wondering if parallel binds with different 'step' values
could occur.
Because different 'step' values can lead to different 'clockOffset'.
It is possible, but this isn't a concern. This code path is reached only
when synchronization is being performed (not regular binds). This means
that the clockOffset value is currently wildly incorrect. We are trying
to move this value to something roughly correct. For various reasons, we
can't get this value exactly. So if parallel authentication has
succeeded, either of the resulting step values is correct.
Thanks Nathaniel for the explanations.
The fix is fine for me and for me it is a ACK.
thanks
thierry
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