Cyrus Sieve futures

Anatoli me at
Tue Feb 7 21:05:03 EST 2017

Bron, do you mean Sieve is separated from the rest of the Cyrus code or 
that inside Sieve code there's separation for pure data processing 
(without syscalls) and I/O & other resources handling, processes/threads 
management, etc.? I my previous mail I was meaning the later.

If it's already done, that's great and everything is ready to define the 
format for the "results" file and proceed with the seccomp 
implementation, if all agree that this is a needed change.

*From:* Bron Gondwana Via Cyrus-devel
*Sent:* Tuesday, February 07, 2017 07:01
*To:* Cyrus-devel
*Subject:* Re: Cyrus Sieve futures

Actually, that's pretty much already done, the separation.  Sieve, more 
than any other part of the Cyrus code, is very decoupled.  It used to be 
a separate CVS repository once upon a time.


On Tue, 7 Feb 2017, at 18:36, Anatoli via Cyrus-devel wrote:
> Hi Ken,
> I don't have any special uses for Sieve apart from the most basic 
> ones, but I would like to ask you if you see it feasible, as part of 
> this work, to separate the "numbers crunching" (e.g. rules matching, 
> transformations, etc.) code from the I/O code (that is responsible for 
> manipulating files, communicating with other processes, etc.)?
> My idea is to isolate and safeguard Sieve's "numbers crunching" code 
> with <> seccomp 
> <>, which basically 
> only allows to execute userland code (i.e. no syscalls, etc.) and 
> read/write to already-open file descriptors. This should reduce 
> currently broad attack surface to some really exotic bugs in the Linux 
> kernel (up to now just one significant bug for strict seccomp bypass 
> was discovered (CVE-2009-0835 in 2.6 kernel 8 years ago), soon after 
> this functionality was implemented).
> One of possible architectures could be described this way (similar to 
> Postfix architecture <>):
>  1. Sieve daemon receives an incoming data for processing and stores
>     it in a memory buffer (without touching it)
>  2. It creates a new "results" file and opens it for writing
>  3. It forks a process
>  4. The newly created child process switches to seccomp
>  5. It processes the data and writes the results (in a special format)
>     to the "results" file, then exits
>  6. Sieve daemon detects the exit of the child process and reads the
>     "results" file to perform the requested actions, then deletes the file
>  7. If the child is killed (as the result of seccomp restrictions
>     violation) or something is wrong with the format of the "results"
>     file, Sieve daemon quarantines the data and writes an error to the
>     logs
> The format for the "results" file should be simple and well defined, 
> and the code to interpret it should be carefully written. This could 
> be started as a mere adaptation for the new architecture of the 
> current actions processing logic and be progressively improved later. 
> This would be much easier than making the entire Sieve code base and 
> the libraries it uses (e.g. PCRE) reasonably safe (PCRE alone is a 
> huge bag ofvulnerabilities 
> <>, 
> including lots of RCEs).
> Another question (just wondering if it's in your (or other devs) plans 
> and its feasibility): is it practically possible to implement for 
> Sieve something like "run the rules on X folder (+ subfolders)" same 
> way as local rules in most MUAs could be applied to already stored 
> mails? I find lack of this feature as the only (but notable) downside 
> to Sieve vs local rules.
> Regards,
> Anatoli
> *From:* Ken Murchison Via Cyrus-devel
> *Sent:* Monday, February 06, 2017 19:34
> *To:* Cyrus-devel
> *Subject:* Cyrus Sieve futures
>> All,
>> I'm in the process of rewriting the Sieve parser and adding new 
>> extensions for what will become part of Cyrus v3.1.  We currently 
>> support deprecated and non-standardized extensions "imapflags" 
>> (standardized as "imap4flags) and "notify" (standardized as 
>> "enotify").  I'd like to rip out the parser and bytecode generator 
>> for these extensions, and leave just the bytecode executing code for 
>> the deprecated actions "mark", "unmark", and "denotify".
>> Any existing scripts using these actions (or the older "notify" 
>> syntax) would continue to run.  New/updated scripts would have to 
>> switch to using the updated "notify" syntax and replace "mark" and 
>> "unmark" with "setflag"/"addflag" and "removeflag".  Does anyone have 
>> an issue with these changes?
>> Does anyone have any requests for standard extensions that we don't 
>> currently support?  Note that "variables", "mailbox" and "*metadata" 
>> will be in Cyrus 3.0 and "ereject", "editheader", and "extlists" are 
>> already in what will be the 3.1 branch.
>> Extensions that I'm looking at implementing (pretty much because they 
>> are low-hanging fruit) are "duplicate", "environment", and "ihave".  
>> I may also look at "replace" and "extracttext" which would be useful 
>> if we add handling of calendar events to Sieve.

   Bron Gondwana
   brong at

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the Cyrus-devel mailing list