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SubjectRe: perf_event_open+clone = unkillable process
On Fri, Feb 01, 2019 at 06:06:03PM +0100, Dmitry Vyukov wrote:
> On Fri, Feb 1, 2019 at 5:48 PM Dmitry Vyukov <dvyukov@google.com> wrote:
> >
> > Hello,
> >
> > The following program creates an unkillable process that eats CPU.
> > /proc/pid/stack is empty, I am not sure what other info I can provide.
> >
> > Tested is on upstream commit 4aa9fc2a435abe95a1e8d7f8c7b3d6356514b37a.
> > Config is attached.
>
> Looking through other reproducers that create unkillable processes, I
> think I found a much simpler reproducer (below). It's single threaded
> and just setups SIGBUS handler and does timer_create+timer_settime to
> send repeated SIGBUS. The resulting process can't be killed with
> SIGKILL.
> +Thomas for timers.

nice, I managed to kill it by strace ;-)

[jolsa@krava perf]$ strace -p 10725
strace: Process 10725 attached
--- stopped by SIGBUS ---
--- stopped by SIGBUS ---
--- stopped by SIGBUS ---
--- stopped by SIGBUS ---
+++ killed by SIGINT +++

+Oleg

jirka

>
>
> // autogenerated by syzkaller (https://github.com/google/syzkaller)
>
> #define _GNU_SOURCE
>
> #include <endian.h>
> #include <setjmp.h>
> #include <signal.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/syscall.h>
> #include <sys/types.h>
> #include <unistd.h>
>
> static __thread int skip_segv;
> static __thread jmp_buf segv_env;
>
> static void segv_handler(int sig, siginfo_t* info, void* ctx)
> {
> uintptr_t addr = (uintptr_t)info->si_addr;
> const uintptr_t prog_start = 1 << 20;
> const uintptr_t prog_end = 100 << 20;
> if (__atomic_load_n(&skip_segv, __ATOMIC_RELAXED) &&
> (addr < prog_start || addr > prog_end)) {
> _longjmp(segv_env, 1);
> }
> exit(sig);
> }
>
> static void install_segv_handler(void)
> {
> struct sigaction sa;
> memset(&sa, 0, sizeof(sa));
> sa.sa_handler = SIG_IGN;
> syscall(SYS_rt_sigaction, 0x20, &sa, NULL, 8);
> syscall(SYS_rt_sigaction, 0x21, &sa, NULL, 8);
> memset(&sa, 0, sizeof(sa));
> sa.sa_sigaction = segv_handler;
> sa.sa_flags = SA_NODEFER | SA_SIGINFO;
> sigaction(SIGSEGV, &sa, NULL);
> sigaction(SIGBUS, &sa, NULL);
> }
>
> int main(void)
> {
> syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
> install_segv_handler();
> int tid = syscall(__NR_gettid);
> *(uint64_t*)0x20000000 = 0;
> *(uint32_t*)0x20000008 = 7;
> *(uint32_t*)0x2000000c = 4;
> *(uint32_t*)0x20000010 = tid;
> syscall(__NR_timer_create, 0, 0x20000000, 0x20000080);
> *(uint64_t*)0x2004a000 = 0;
> *(uint64_t*)0x2004a008 = 1;
> *(uint64_t*)0x2004a010 = 7;
> *(uint64_t*)0x2004a018 = 0xe4c;
> syscall(__NR_timer_settime, 0, 3, 0x2004a000, 0);
> return 0;
> }

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