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charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 29, 2020 at 9:13 PM Vinicius Costa Gomes wrote: > > Hi, > > "Zhang, Qiang" writes: > > > ________________________________________ > > =E5=8F=91=E4=BB=B6=E4=BA=BA: linux-kernel-owner@vger.kernel.org =E4=BB=A3=E8=A1=A8 syzbot > > =E5=8F=91=E9=80=81=E6=97=B6=E9=97=B4: 2020=E5=B9=B47=E6=9C=8829=E6=97= =A5 13:53 > > =E6=94=B6=E4=BB=B6=E4=BA=BA: davem@davemloft.net; fweisbec@gmail.com; j= hs@mojatatu.com; jiri@resnulli.us; linux-kernel@vger.kernel.org; mingo@kern= el.org; netdev@vger.kernel.org; syzkaller-bugs@googlegroups.com; tglx@linut= ronix.de; vinicius.gomes@intel.com; xiyou.wangcong@gmail.com > > =E4=B8=BB=E9=A2=98: INFO: rcu detected stall in tc_modify_qdisc > > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 181964e6 fix a braino in cmsghdr_from_user_compat_to_ke= rn() > > git tree: net > > console output: https://syzkaller.appspot.com/x/log.txt?x=3D12925e38900= 000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=3Df87a5e4232f= db267 > > dashboard link: https://syzkaller.appspot.com/bug?extid=3D9f78d5c664a8c= 33f4cce > > compiler: gcc (GCC) 10.1.0-syz 20200507 > > syz repro: > > https://syzkaller.appspot.com/x/repro.syz?x=3D16587f8c900000 > > It seems that syzkaller is generating an schedule with too small > intervals (3ns in this case) which causes a hrtimer busy-loop which > starves other kernel threads. > > We could put some limits on the interval when running in software mode, > but I don't like this too much, because we are talking about users with > CAP_NET_ADMIN and they have easier ways to do bad things to the system. Hi Vinicius, Could you explain why you don't like the argument if it's for CAP_NET_ADMIN= ? Good code should check arguments regardless I think and it's useful to protect root from, say, programming bugs rather than kill the machine on any bug and misconfiguration. What am I missing? Also are we talking about CAP_NET_ADMIN in a user ns as well (effectively nobody)?