20 Apr
2012
20 Apr
'12
5:03 p.m.
Yes, Peter's commit fixed the issue I saw. It removed the srand() from
RLS so that it no longer affected the Via branch param generator.
Do you think that the Via branch should be protected against this? For
example using the srutils unique ID function instead of rand()?
Hugh
On 20/04/2012 11:39, Daniel-Constantin Mierla wrote:
Hello,
had not time yet to get and look properly at this thread, is the issue
fixed by Peter's commit related to some srand() usage?
Cheers,
Daniel
On 4/16/12 1:15 PM, Hugh Waite wrote:
--
Hugh Waite
Senior Design Engineer
Crocodile RCS Ltd.
I now realise that rls was deliberately using the
same sequence of
random numbers to satisfy RFC4662 §5.5
5.5. Instance Attributes
Each resource element contains zero or more instance elements. These
instance elements are used to represent a single notifier for the
resource. For event packages that allow forking, multiple virtual
subscriptions may exist for a given resource. Multiple virtual
subscriptions are represented as multiple instance elements in the
corresponding resource element. For subscriptions in which forking
does not occur, at most one instance will be present for a given
resource.
The "id" attribute contains an opaque string used to uniquely
identify the instance of the resource. The "id" attribute is unique
only within the context of a resource. Construction of this string
is an implementation decision. Any mechanism for generating this
string is valid, as long as uniqueness within the resource is
assured.
Seeding srand() with the values 0, 1, 2... always gives the same
sequence of ID strings. Maybe someone has an opinion on whether this
should be implemented differently, or whether a value should be
stored for situations where multiple resource instances are
removed/reordered.
Maybe kamailio should use a unique ID (from srutils) in the Via
header for uac requests (in modules/tm/h_table.h) anyway, to prevent
a module from affecting Via branch params by using srand().
Regards,
Hugh
On 13/04/2012 15:26, Hugh Waite wrote:
--
Daniel-Constantin Mierla
Kamailio Advanced Training, April 23-26, 2012, Berlin, Germany
http://www.asipto.com/index.php/kamailio-advanced-training/ Hi,
One of the places that uses rand() is
modules/tm/h_table.c:init_synonym_id . Requests generated by
kamailio (as a uac) use this to generate the Via branch tag. If any
module calls srand(), it affects the Via branch for subsequent
requests.
The actual bug we found is in rls/notify.c:generate_string(). The
add_resource_instance() function will re-seed srand() with 0 (zero),
leading to nearly every NOTIFY sent by rls having the same "random"
number in the Via branch. I am sure this was the cause of lost
replies, timeouts and dropped subscriptions that we were seeing (and
appears to have gone away after removing it).
Although, I could just remove the srand from rls notify.c, I
wondered if it should be using a different random function, and also
whether init_synonym_id should use something more unique for the Via
branch parameter.
A quick check has shown a few places that call srand() within the
code, although they probably have less drastic consequences.
Regards,
Hugh
On 13/04/2012 14:01, Daniel-Constantin Mierla wrote:
--
Hugh Waite
Senior Design Engineer
Crocodile RCS Ltd.
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sr-dev(a)lists.sip-router.org
http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-dev Hello,
I haven't looked at the issue reported by Hugh, so by now just
comments on srutils/sruid.
The idea was to have an unique id generator without linking to an
external library -- my first purpose was to use it for temporary
GRUU ids (RFC5627), I am just about to push to master the gruu
support in registrar/usrloc.
Then I thought it might be useful in other places, such as dialog
unique id.
I added it as part of lib, since its target usage was for modules
so far, but if needed for some core processing, the two files
(rather small by now) can be moved in the core.
Cheers,
Daniel
On 4/13/12 2:50 PM, Henning Westerholt wrote:
> On Friday 13 April 2012, Hugh Waite wrote:
>> I have a question about random number generation within kamailio.
>>
>> A number of modules use rand() to get a random value and in some
>> places
>> is re-seeding with srand(). I believe this is dangerous because
>> rand()
>> is used in the Via branch tag generator.
>> We have detected some real bugs (where srand is reseeding with 0 for
>> every message, causing transaction mis-matching) but I'm not sure
>> of the
>> correct way to fix this (other than remove srand()).
>>
>> Should all modules be using a 'core' random function (e.g. in
>> srutils?)
>> ? And if so, is this library documented?
>>
>> Regards,
>> Hugh
> Hi Hugh,
>
> for the purpose getting a pseudo-random number (i.e. not for
> cryptographic
> functionality) we should consolidate on a single random function.
> There is the
> recent introduced srutils/sruid code, then there exists a (IMHO
> stronger)
> pseudo-random number generator in rand/fastrand and then there is
> of course
> rand().
>
> Maybe Daniel can comment about the purpose of the srutils
> function, IMHO
> consolidating on fastrand or one of the stronger function (d_rand
> etc..) from
> stdlib.h would be fine.
>
> The re-seeding the internal state of rand() with srand during
> runtime sounds
> wrong toe me and should be removed/ fixed.
>
> Viele Grüße/ best regards,
>
> Henning Westerholt
>
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