Re: [PATCH net] sctp: not allow transport timeout value less than HZ/5 for hb_timer

[David Miller <davem@davemloft.net>]

From: Xin Long <lucien.xin@gmail.com>
Date: Tue,  5 Jun 2018 12:16:58 +0800

> syzbot reported a rcu_sched self-detected stall on CPU which is caused
> by too small value set on rto_min with SCTP_RTOINFO sockopt. With this
> value, hb_timer will get stuck there, as in its timer handler it starts
> this timer again with this value, then goes to the timer handler again.
> 
> This problem is there since very beginning, and thanks to Eric for the
> reproducer shared from a syzbot mail.
> 
> This patch fixes it by not allowing sctp_transport_timeout to return a
> smaller value than HZ/5 for hb_timer, which is based on TCP's min rto.
> 
> Note that it doesn't fix this issue by limiting rto_min, as some users
> are still using small rto and no proper value was found for it yet.
> 
> Reported-by: syzbot+3dcd59a1f907245f891f@syzkaller.appspotmail.com
> Suggested-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied and queued up for -stable, thanks Xin.