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Date: Thu, 10 Feb 2022 12:58:07 -0600 From: "Eric W. Biederman" <ebiederm@...ssion.com> To: Kees Cook <keescook@...omium.org> Cc: Robert Święcki <robert@...ecki.net>, Andy Lutomirski <luto@...capital.net>, Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH 0/3] signal: HANDLER_EXIT should clear SIGNAL_UNKILLABLE Kees Cook <keescook@...omium.org> writes: > On Thu, Feb 10, 2022 at 12:17:50PM -0600, Eric W. Biederman wrote: >> Kees Cook <keescook@...omium.org> writes: >> >> > Hi, >> > >> > This fixes the signal refactoring to actually kill unkillable processes >> > when receiving a fatal SIGSYS from seccomp. Thanks to Robert for the >> > report and Eric for the fix! I've also tweaked seccomp internal a bit to >> > fail more safely. This was a partial seccomp bypass, in the sense that >> > SECCOMP_RET_KILL_* didn't kill the process, but it didn't bypass other >> > aspects of the filters. (i.e. the syscall was still blocked, etc.) >> >> Any luck on figuring out how to suppress the extra event? > > I haven't found a good single indicator of a process being in an "I am dying" > state, and even if I did, it seems every architecture's exit path would > need to add a new test. The "I am dying" state for a task is fatal_signal_pending, at least before get_signal is reached, for a process there is SIGNAL_GROUP_EXIT. Something I am busily cleaning up and making more reliable at the moment. What is the event that is happening? Is it tracehook_report_syscall_exit or something else? >From the bits I have seen it seems like something else. > The best approach seems to be clearing the TIF_*WORK* bits, but that's > still a bit arch-specific. And I'm not sure which layer would do that. > At what point have we decided the process will not continue? More > than seccomp was calling do_exit() in the middle of a syscall, but those > appear to have all been either SIGKILL or SIGSEGV? This is where I get confused what TIF_WORK bits matter? I expect if anything else mattered we would need to change it to HANDLER_EXIT. I made a mistake conflating to cases and I want to make certain I successfully separate those two cases at the end of the day. Eric
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