[systemd-devel] BUG: several bugs in core/main.c (v218)

[Andrei Borzenkov]

В Sun, 25 Jan 2015 03:37:09 +0100
"Tomasz Pawlak" <tomazzi at wp.pl> пишет:

> core/main.c:1519
>       /* Make sure we leave a core dump without panicing the
>        * kernel. */
>       if (getpid() == 1) {
>               install_crash_handler();
> 
>               r = mount_cgroup_controllers(arg_join_controllers);
>               if (r < 0)
>                       goto finish;
>       }
> 
> core/main.c:226
> static void install_crash_handler(void) {
>       struct sigaction sa = {
>               .sa_handler = crash,
>               .sa_flags = SA_NODEFER,
>       };
> 
>       sigaction_many(&sa, SIGNALS_CRASH_HANDLER, -1);
> }
> 
> /shared/util.c:2207
> int sigaction_many(const struct sigaction *sa, ...) {
>       va_list ap;
>       int r = 0, sig;
> 
>       va_start(ap, sa);
>       while ((sig = va_arg(ap, int)) > 0)
>               if (sigaction(sig, sa, NULL) < 0)
>                       r = -errno;
>       va_end(ap);
> 
>       return r;
> }
> 
> shared/def.h:40
> #define SIGNALS_CRASH_HANDLER SIGSEGV,SIGILL,SIGFPE,SIGBUS,SIGQUIT,SIGABRT
> 
> 
> BUGS:
> 1. Ignoring return value from sigaction_many(): all sig handlers can silently fail to install, thus leaving the whole process unprotected

What do you suggest to do in this case? We are running as PID1, we
cannot just error exit. 

> 
> 2. SIGSEGV should be catched by a handler running on a separate stack (SA_ONSTACK) - otherwise it can cause segfault itself, when the first SIGSEGV which triggered the handler is caused by stack overflow.
> 
> 3. SA_NODEFER makes no sense, since the handler is expected to catch only first critical signal. With SA_NODEFER nesting of signals is possible, what can cause unpredictable results, including uncatched stack overflow caused by the handler itself.
> 
> Regards.
> 
> 
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