At the some point of FreeBSD development it became apparent that in order to help developers to perform timely features merge from the developent branch (aka FreeBSD-CURRENT) into stable branch (aka FreeBSD-STABLE) some form of automatic system, which will track outstanding merges and notify appropriate developer when the time for a merge has come, is necessary. Otherwise, developers are often stick with two extreme cases: some of them forget to merge changes, even those that are clearly safe to merge, while some performing merge shorly after committing the change into a development branch fearing that if the merge is delayed they will forget to do it at all. Both those cases introduce problems to the Project, because in the former case stable branch experiences feature stagnation, while the latter leads to stability degradation, as the features are often being merged without proper testing in the development branch.
To address the problem the MFCns service was created. It works as follows: when committing a change to a development branch a developer specifies a time period during which the appropriate change has to be tested before being merged into a stable branch. The system notes this request and after this time period is over, it notifies the developer about that fact. It is important to emphasise that the final decision as to whether to merge change in question or not is up to the developer, because at that time he might have received an information that makes a merge undesirable (e.g. bug report from user who experieces problem with the change, security advisory from a security officer, negative feedback from other developers and so on).
When designing the MFCns the following goals were attacked:
The service is implemented in two parts. First part written in C is a
simple mail filter, which reads mail message (one a time) from the standard
input, looks for a set of patterns and if all conditions are satisfied
writes copy of message into a specially designated spool folder. To avoid
using locks the filter initially writes message into a temporary folder and
then moves it into a spool folder using rename(2) system call, which is
guranteed to be atomic operation. Obviously this means that both temporary
and spool folders have to reside on the same filesystem, so please keep
this in mind if you are going to use the service elsewhere. The name of the
file in the spool directory is generated using value in the "Message-ID"
field of the message, allowing to avoid duplicated notification if for
some reason more than one copy of the same commit message will be received
by the filter. Since e-mail messages is considered as an "unsafe" medium,
the filter puts significant restrictions on the part of the "Message-ID"
field to be used as the filename, so that it is impossible to use forged
message to overwrite a file outside of the spool directory.
The second part of the service does most of the job, which includes spool and queue processing and sending reminders. Since this part is not speed-critical (it only invoked once a day), it was implemented in Python. Its operation consists of the following phases:
spool folder, identifies the date at which each notification is to be
delivered and moves messages into the queue directory. In the queue
folder messages are placed into subfolders named by the date when each
notification is due (YYYYMMDD), so that all notifications which should be
delivered at the same date end up in the same subfolder. Such design
simplifies future queue processing as well as gurantees that each message
is parsed only twice - first time when it is moved from the spool to
queue to calculate the date when notification have to be sent and
second time when the service actually sends a notification to identify to
whom send it;queue
directory and identifies which notifications are ready to be sent. It
parses each request from the ready subset, identifies recepient,
generates outgoing message and sends it out. Once notification is sent
the notification request is deleted from the queue.Since e-mail is widely known as a not very safe medium, the service was designed with security in mind, however no formal security audit was performed yet. The part of the service written in C doesn't use any statically allocated string buffers, so it should not be vulnerable to various smash-the-stack attacks, while part written in Python was specially tailored to not pass any of the shell metacharacters to a subshell invoked for sending notification. All this makes a potential attack pretty meaningless, because all that an attacker could do is to make service sending fake MFC notifications, but he can do this even without any help from the service.
https://github.com/sobomax/mfc_notifications
If you have any questions/suggestions/requests please don't hesitate to contact Maxim Sobolev sobomax@FreeBSD.org. Also, if possible, drop me a line if you will find this code useful somewhere outside of the FreeBSD Project.
MFC Notification Service Statistics
-----------------------------------
Period: Wed May 9 00:22:02 2001 - Thu May 9 00:23:03 2019
Total number of notifications sent: 41356
Committer MFCs % total
--------- ---- -------
kib 2998 7.25
jhb 1544 3.73
hselasky 1462 3.54
ngie 1426 3.45
rwatson 1217 2.94
mav 1007 2.43
trasz 953 2.30
markj 938 2.27
pjd 922 2.23
avg 902 2.18
delphij 861 2.08
dim 724 1.75
sephe 703 1.70
tuexen 665 1.61
bz 652 1.58
brueffer 581 1.40
bdrewery 564 1.36
pfg 540 1.31
ae 539 1.30
des 509 1.23
marius 474 1.15
rmacklem 469 1.13
emaste 439 1.06
np 430 1.04
asomers 429 1.04
arybchik 409 0.99
gjb 400 0.97
eadler 390 0.94
sam 385 0.93
ume 357 0.86
alc 345 0.83
maxim 332 0.80
mm 311 0.75
mjacob 271 0.66
nwhitehorn 260 0.63
sobomax 257 0.62
jilles 229 0.55
brooks 211 0.51
bapt 210 0.51
yar 204 0.49
ru 201 0.49
dteske 196 0.47
sbruno 192 0.46
smh 189 0.46
jhibbits 186 0.45
rpaulo 183 0.44
luigi 182 0.44
emax 180 0.44
gad 180 0.44
cy 174 0.42
dchagin 171 0.41
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xride 1 0.00-- Maxim Sobolev sobomax@FreeBSD.org