On Sun, May 20, 2018 at 04:26:03PM +0800, Xin Long wrote: > On Sat, May 19, 2018 at 11:57 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote: > > SCTP experts, please take a look. > > > > On 05/19/2018 08:55 AM, syzbot wrote: > >> Hello, > >> > >> syzbot found the following crash on: > >> > >> HEAD commit: 73fcb1a370c7 Merge branch 'akpm' (patches from Andrew) > >> git tree: upstream > >> console output: https://syzkaller.appspot.com/x/log.txt?x=1462ec0f800000 > >> kernel config: https://syzkaller.appspot.com/x/.config?x=f3b4e30da84ec1ed > >> dashboard link: https://syzkaller.appspot.com/bug?extid=3dcd59a1f907245f891f > >> compiler: gcc (GCC) 8.0.1 20180413 (experimental) > >> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1079cf8f800000 > Thank you. > The Reproducer is more than helpful. > > setsockopt$inet_sctp6_SCTP_RTOINFO(r0, 0x84, 0x0, > &(0x7f0000000140)={0x0, 0x6, 0x7, 0x4}, 0x10) > > It set rto_min=6 and rto_max=7, these are too small values. > t3_rtx timer works fine with it. But hb_timer will get stuck there, as > in its timer handler it starts this timer again with this value, then > it goes to the timer handler again... Nice, thanks Xin. > > HB has to repeat this and the hb timer's expire may also have to use > 'trans->rto >> 1 ...' stuff. But we can limit the RTO's min value, like > HZ/20, which is 'Try again later.' number used when sock lock is > owned by others in all timer handlers. I think a good fix for this is to not allow the application to go below net.sctp.rto_min, and neither above net.sctp.rto_max. Then they can even be close to each other, won't be an issue, as long as rto_min is something sensible. Which then brings it to the second step of a fix: to restrict rto_min to be >= HZ/5 (copying from TCP here). -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
