Messages in this thread | | | Date | Mon, 11 Feb 2019 16:18:40 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/2] signal: Better detection of synchronous signals |
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Eric, I'll try to finally read the whole thread later, probably I missed something, but...
On 02/07, Eric W. Biederman wrote: > > Recently syzkaller was able to create unkillablle processes by > creating a timer that is delivered as a thread local signal on SIGHUP, > and receiving SIGHUP SA_NODEFERER. Ultimately causing a loop failing > to deliver SIGHUP but always trying. > > When the stack overflows delivery of SIGHUP fails and force_sigsegv is > called. Unfortunately because SIGSEGV is numerically higher than > SIGHUP next_signal tries again to deliver a SIGHUP.
Confused... In this particular case next_signal() should return SIGSEGV because it must be pending too and SYNCHRONOUS_MASK doesn't include SIGHUP.
Not that it really matters, the timer can deliver another SYNCHRONOUS_MASK signal < SIGSEGV, just I am trying to understand what have I missed...
> + /* > + * Check if there is another siginfo for the same signal. > + */ > + list_for_each_entry_continue(q, &pending->list, list) { > + if (q->info.si_signo == sync->info.si_signo) > + goto still_pending; > + }
But this must not be possible? SYNCHRONOUS_MASK doesn't include real-time signals, we can't have 2 siginfo's for the same signal < SIGRTMIN.
Oleg.
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