Rooting Galaxy S2 Jelly Bean is easily done nowadays, no need of flashing any insecure kernel or any third party software. This is the most easiest method of rooting Jelly Bean android phone without any risk of blocking it.
Requirements for rooting galaxy S2
===> Samsung Galaxy S2 with Jelly Bean 4.1.2 XXLSJ firmware
===>Battery charge more than 50%.
===> Backup all your important data.
How to Root Samsung Galaxy S2 4.1.2 Jelly Bean
2.Copy XXLSJ-ROOT-CWM6(renjusblog.com).zip file to external SD card. Not into internal SD card
3.Switch Off the phone.
4.Press Volume Up + Home button and then still holding these buttons press the Power button. Your phone will now boot into the recovery mode.
5.Select apply update from external storage.At the Android system recovery screen.
Now Select the file you have copied earlier (2) to your external Sd card.
6.Reboot your phone.