Re: [DNG] Linux system can be brought down by sending SIGILL to Systemd - PID 1 is killed it seems
> > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done > > > > I found out PID 1 is killed when I tried to reboot: > > # reboot > > Failed to open /dev/initctl: No such device or address > > Failed to talk to init daemon. > > > > So I will have to use SysReq keys > > > > Can somebody, please link me to the Documentation Files on those > SysReq keys? Thanks! > > Kenneth Parker > > > > > https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html
Re: [DNG] Linux system can be brought down by sending SIGILL to Systemd - PID 1 is killed it seems
On Sat, May 25, 2019 at 08:35:45AM -0400, Kenneth Parker wrote: [...] > Can somebody, please link me to the Documentation Files on those SysReq > keys? Thanks! https://en.wikipedia.org/wiki/Magic_SysRq_key Cheers -- t signature.asc Description: Digital signature
Re: [DNG] Linux system can be brought down by sending SIGILL to Systemd - PID 1 is killed it seems
On Sat, May 25, 2019, 5:45 AM arne wrote: > On Sat, 25 May 2019 00:21:07 +0200 > arne wrote: > > > On Fri, 24 May 2019 23:43:49 +0200 > > arne wrote: > > > > > On Fri, 24 May 2019 14:01:35 -0700 > > > Fred wrote: > > > > > > > Hello, > > > > I subscribe to the Devuan Linux mailing list. This posting just > > > > arrived and it appears quite important to Debian. > > > > > > > > Forwarded Message > > > > Subject: [DNG] Linux system can be brought down by sending > > > > SIGILL to Systemd > > > > Date: Fri, 24 May 2019 22:04:34 +0200 > > > > From: Martin Steigerwald > > > > To: DNG > > > > > > > > > > > > > > > > Hi! > > > > > > > > Today in a Linux training a participant attempted to bring down > > > > Debian workstation with Systemd by sending signals to PID 1 as I > > > > invited them to try to bring down PID 1 while thinking for myself > > > > that this would not be possible from my past experiences about > > > > trying to bring down PID 1 – init – myself. > > > > > > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done > > > ...^C > > > > > > no problem here > > > kernel 5.1.4 stretch amd64 with systemd > > > > > > > Perhaps that test was a little too short so I let it run a little > > longer: > > > > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done > > > ..^C > > > > again no problem here. > > > > I had no fear to run the script as I use systemd, so I know how to > > use the SysReq keys very well ;) > > > > > > > > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done > > I found out PID 1 is killed when I tried to reboot: > # reboot > Failed to open /dev/initctl: No such device or address > Failed to talk to init daemon. > > So I will have to use SysReq keys > Can somebody, please link me to the Documentation Files on those SysReq keys? Thanks! Kenneth Parker > >
Re: [DNG] Linux system can be brought down by sending SIGILL to Systemd
On Sat, May 25, 2019 at 10:25:26AM +0300, Reco wrote: [...] > Seems harmless to me as one needs to be root to send signals to PID 1. This is *exactly* the point. If you are root, there are far more creative (and fun) ways to bring down your system, regardless of how your init process is called. I'll pay a virtual beer [1] to the first one here which comes with a shell one-liner overwriting the first gig of init's heap space with /dev/urandom (say the modern and correct moral equivalent of dd if=/dev/urandom of=/proc/1/mem bs=4096 count=256k ... shouldn't be hard). Cheers [1] exchangeable by some physical $beverage of choice should we meet in person. -- t signature.asc Description: Digital signature
Re: [Possibly fake news] [DNG] Linux system can be brought down by sending SIGILL to Systemd
to...@tuxteam.de (12019-05-25): > That means that to send SIGILL to pid 1 you most probably gotta be > root (systemd or not). And then, there are more classy ways to bring > your system down anyway. > > Folks, please double-check that stuff before reposting. I don't want > the Debian mailing list to become Fakebook or Twitter. No need to double check: with a little common sense and technical competence, a single check is enough. Remember folks: The proof that systemd is evil is that "cat /lib/systemd/systemd > /dev/sda" will likely make your system unbootable. Regards, -- Nicolas George signature.asc Description: PGP signature
Re: [DNG] Linux system can be brought down by sending SIGILL to Systemd - PID 1 is killed it seems
On Sat, 25 May 2019 00:21:07 +0200 arne wrote: > On Fri, 24 May 2019 23:43:49 +0200 > arne wrote: > > > On Fri, 24 May 2019 14:01:35 -0700 > > Fred wrote: > > > > > Hello, > > > I subscribe to the Devuan Linux mailing list. This posting just > > > arrived and it appears quite important to Debian. > > > > > > Forwarded Message > > > Subject: [DNG] Linux system can be brought down by sending > > > SIGILL to Systemd > > > Date: Fri, 24 May 2019 22:04:34 +0200 > > > From: Martin Steigerwald > > > To: DNG > > > > > > > > > > > > Hi! > > > > > > Today in a Linux training a participant attempted to bring down > > > Debian workstation with Systemd by sending signals to PID 1 as I > > > invited them to try to bring down PID 1 while thinking for myself > > > that this would not be possible from my past experiences about > > > trying to bring down PID 1 – init – myself. > > > > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done > > ...^C > > > > no problem here > > kernel 5.1.4 stretch amd64 with systemd > > > > Perhaps that test was a little too short so I let it run a little > longer: > > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done > ..^C > > again no problem here. > > I had no fear to run the script as I use systemd, so I know how to > use the SysReq keys very well ;) > > > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done I found out PID 1 is killed when I tried to reboot: # reboot Failed to open /dev/initctl: No such device or address Failed to talk to init daemon. So I will have to use SysReq keys
Re: [DNG] Linux system can be brought down by sending SIGILL to Systemd
On 2019-05-25 08:25, Reco wrote: again no problem here. Stretch's systemd: # kill -ILL 1 Message from syslogd@xxx at May 25 10:19:09 ... systemd[1]: Caught , dumped core as pid 822. ... systemd[1]: Freezing execution. The userspace and the kernel will work after this, but anything that's related to systemd (including poweroff and shutdown) just hangs. Seems harmless to me as one needs to be root to send signals to PID 1. If you are going to kill off processes as root I'd expect things to be unhappy. I once accidentally removed everything from / down and that stopped it working as well. mick -- Key ID4BFEBB31
Re: [Possibly fake news] [DNG] Linux system can be brought down by sending SIGILL to Systemd
On 2019-05-25, wrote: > > Folks, please double-check that stuff before reposting. I don't want > the Debian mailing list to become Fakebook or Twitter. > Or Der Spiegel. https://www.theatlantic.com/international/archive/2019/01/der-spiegal-fabrication-scandal-global/579889/ -- “Decisions are never really made – at best they manage to emerge, from a chaos of peeves, whims, hallucinations and all around assholery.” – Thomas Pynchon
Re: [DNG] Linux system can be brought down by sending SIGILL to Systemd
Hi. On Sat, May 25, 2019 at 12:21:07AM +0200, arne wrote: > On Fri, 24 May 2019 23:43:49 +0200 > arne wrote: > > > On Fri, 24 May 2019 14:01:35 -0700 > > Fred wrote: > > > > > Hello, > > > I subscribe to the Devuan Linux mailing list. This posting just > > > arrived and it appears quite important to Debian. > > > > > > Forwarded Message > > > Subject: [DNG] Linux system can be brought down by sending > > > SIGILL to Systemd > > > Date: Fri, 24 May 2019 22:04:34 +0200 > > > From: Martin Steigerwald > > > To: DNG > > > > > > > > > > > > Hi! > > > > > > Today in a Linux training a participant attempted to bring down > > > Debian workstation with Systemd by sending signals to PID 1 as I > > > invited them to try to bring down PID 1 while thinking for myself > > > that this would not be possible from my past experiences about > > > trying to bring down PID 1 – init – myself. > > > > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done > > ...^C > > > > no problem here > > kernel 5.1.4 stretch amd64 with systemd > > > > Perhaps that test was a little too short so I let it run a little > longer: > > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done > ..^C > > again no problem here. Stretch's systemd: # kill -ILL 1 Message from syslogd@xxx at May 25 10:19:09 ... systemd[1]: Caught , dumped core as pid 822. ... systemd[1]: Freezing execution. The userspace and the kernel will work after this, but anything that's related to systemd (including poweroff and shutdown) just hangs. Seems harmless to me as one needs to be root to send signals to PID 1. > I had no fear to run the script as I use systemd, so I know how to > use the SysReq keys very well ;) There's also that /proc/sysrq-trigger in the case the console isn't accessible. Reco
[Possibly fake news] [DNG] Linux system can be brought down by sending SIGILL to Systemd
On Fri, May 24, 2019 at 02:01:35PM -0700, Fred wrote: > Hello, > I subscribe to the Devuan Linux mailing list. This posting just > arrived and it appears quite important to Debian. [about sending SIGILL to systemd] This is most probably fake news. You have to have appropriate permissions to send *any* signal to a proces. From the kill(2) man page "For a process to have permission to send a signal, it must either be privileged (under Linux: have the CAP_KILL capability in the user namespace of the target process), or the real or effective user ID of the sending process must equal the real or saved set-user-ID of the target process. In the case of SIGCONT, it suffices when the sending and receiving processes belong to the same session. (Historically, the rules were different; see NOTES.)" That means that to send SIGILL to pid 1 you most probably gotta be root (systemd or not). And then, there are more classy ways to bring your system down anyway. Folks, please double-check that stuff before reposting. I don't want the Debian mailing list to become Fakebook or Twitter. Cheers -- tomás signature.asc Description: Digital signature
Re: [DNG] Linux system can be brought down by sending SIGILL to Systemd
On Fri, 24 May 2019 23:43:49 +0200 arne wrote: > On Fri, 24 May 2019 14:01:35 -0700 > Fred wrote: > > > Hello, > > I subscribe to the Devuan Linux mailing list. This posting just > > arrived and it appears quite important to Debian. > > > > Forwarded Message > > Subject:[DNG] Linux system can be brought down by sending > > SIGILL to Systemd > > Date: Fri, 24 May 2019 22:04:34 +0200 > > From: Martin Steigerwald > > To: DNG > > > > > > > > Hi! > > > > Today in a Linux training a participant attempted to bring down > > Debian workstation with Systemd by sending signals to PID 1 as I > > invited them to try to bring down PID 1 while thinking for myself > > that this would not be possible from my past experiences about > > trying to bring down PID 1 – init – myself. > > # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done > ...^C > > no problem here > kernel 5.1.4 stretch amd64 with systemd > Perhaps that test was a little too short so I let it run a little longer: # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done ..^C again no problem here. I had no fear to run the script as I use systemd, so I know how to use the SysReq keys very well ;)
Re: [DNG] Linux system can be brought down by sending SIGILL to Systemd
On Fri, 24 May 2019 14:01:35 -0700 Fred wrote: > Hello, > I subscribe to the Devuan Linux mailing list. This posting just > arrived and it appears quite important to Debian. > > Forwarded Message > Subject: [DNG] Linux system can be brought down by sending > SIGILL to Systemd > Date: Fri, 24 May 2019 22:04:34 +0200 > From: Martin Steigerwald > To: DNG > > > > Hi! > > Today in a Linux training a participant attempted to bring down Debian > workstation with Systemd by sending signals to PID 1 as I invited them > to try to bring down PID 1 while thinking for myself that this would > not be possible from my past experiences about trying to bring down > PID 1 – init – myself. # while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done ...^C no problem here kernel 5.1.4 stretch amd64 with systemd
Fwd: [DNG] Linux system can be brought down by sending SIGILL to Systemd
Hello, I subscribe to the Devuan Linux mailing list. This posting just arrived and it appears quite important to Debian. Forwarded Message Subject: [DNG] Linux system can be brought down by sending SIGILL to Systemd Date: Fri, 24 May 2019 22:04:34 +0200 From: Martin Steigerwald To: DNG Hi! Today in a Linux training a participant attempted to bring down Debian workstation with Systemd by sending signals to PID 1 as I invited them to try to bring down PID 1 while thinking for myself that this would not be possible from my past experiences about trying to bring down PID 1 – init – myself. While sending SIGKILL to Systemd did not have any effect, sending SIGILL – illegal instruction – to it brought the machine to an halt. I reproduced it with while true; do kill -ILL 1 ; echo -n "." ; sleep 0.5 ; done on my training workstation (Debian 9.9 with Systemd 232 and 4.9.0-9 Debian Kernel with MDS mitigation). The mouse pointer froze and the machine did not even respond to ping anymore! According to participants about 4 to 5 times sending the signal would be enough to bring down a workstation with Systemd as PID 1. Despite all the bugs and issues I have seen or read about with Systemd I was very surprised about that result. Curiously I attempted the same with the Debian on my laptop that I switched to SysVInit and elogind. As the elogind stuff mostly works I think I will switch it to Devuan once I come around to it. I am able to run while true; do kill -ILL 1 ; echo -n "." ; done against SysVinit's "init" process without any issue for minutes (Debian Sid with sysvinit 2.93-8 and self-compiled 5.1.2 kernel, also with MDS mitigation). It is even running while I write this mail normally now. Also the participants found in the manpage kill(2): NOTES The only signals that can be sent to process ID 1, the init process, are those for which init has explicitly installed sig‐ nal handlers. This is done to assure the system is not brought down accidentally. So if that is actually true, then it appears that Systemd initiates a signal handler for SIGILL for whatever reason. I pondered about writing a bug report to Systemd developers, but honestly from my past experiences with upstream feedback about bug reports regarding Systemd I then decided not to bother about it. I am not willing to take in and deal with any more "this is by design, go away" or "this works as intended, go away" kind of responses. I am not interested in Systemd to a larger extent than teaching participants of my training what they need to know about it, when they have to deal with it due to distribution choices made at their employer. And yes, I also have a slide that summarizes critique about it, complete with links, so they can make up their own opinion. And no, for me it is not black and white, but my own decision is to go without Systemd. This is another reason for me to start to provide Devuan VMs in the Proxmox VE environment I use to provide VMs of various distributions to the participants of my trainings. So participants can have a look at it and do exercises with it if they like. I already started to incorporate information about Devuan in some of my slides. I share it here not to invite another bashing about Systemd, we really do not need to go there, but instead can focus on strengthening the alternatives. But I share it here to provide another reason to use a Systemd-free distribution like Devuan. I also share it as an example of the robustness of the SysVInit init process! Thanks, -- Martin ___ Dng mailing list d...@lists.dyne.org https://mailinglists.dyne.org/cgi-bin/mailman/listinfo/dng
