According to reports, former Prime Minister of Malaysia, Najib Razak is currently doing his PHD in prison. 

However, he has not been allowed access to any gadgets whatsoever. 

Najib signed up for his post-graduate studies while serving his 12-year jail term, and home minister confirmed that he is not allowed to use a laptop or access the internet while in Kajang Prison. 

But he also noted that  it was still possible for him to post social media posts through his social media team doing so on his behalf, as long as they are able to access his accounts.

"So does he have that facility? The answer is no. He doesn't have, take it from me, the most legitimate and authoritative source, he doesnt have any access to any gadget", he said.

As for what Najib is doing now, he fills his time by continuing his studies. He is now continuing his studies at the post-graduate level.

The minister also explained that there are prisoners who obtain a Masters degree or even complete their PhD studies by the time they finish serving their jail term at Kajang Prison.

But how?

According to wikipedia, prison education is actually available. 

Courses can include basic literacy programs, secondary school equivalency programs, vocational education, and tertiary education. 

Other activities such as rehabilitation programs, physical education, and arts and crafts programs may also be considered a form of prison education. 

They are typically provided, managed, and funded by the prison system, though inmates may be required to pay for distance education programs. 

It also varies depending on country.