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SubjectRe: arch/tile/kernel/hardwall.c:do_hardwall_trap unsafe/wrong usage of ->sighand
On 4/21/2011 9:03 PM, Oleg Nesterov wrote:
> On 04/18, Oleg Nesterov wrote:
>> On 04/16, Matt Fleming wrote:
>>> 3. I suspect most people find the rules of ->sighand pretty
>>> confusing. Just look at
>>>
>>> arch/tile/kernel/hardwall.c:do_hardwall_trap()
>>>
>>> the use of siglock there looks buggy to me.
>> Indeed, I agree. It shouldn't use __group_send_sig_info() at all.
>> I'll send the patch. Nobody outside of signal code should play with
>> ->sighand, this is almost always wrong.
> Hmm. It turns out, I can't make the patch because I do not understand
> what this code tries to do.
>
> hardwall_activate() adds the thread to hardwall_list, but do_hardwall_trap()
> sends the signal to the whole process. I know nothing about arch/tile and
> probably this is correct, but could you confirm this?

Yes, the intended behavior is to send the signal to the process, as a way
of indicating the OS's displeasure with sending a malformed packet on the
user network. But I think sending it to the specific thread is reasonable
too; I don't have a strong preference in this design.

> Note that SIGILL can be delivered to another thread in the thread-group, is
> it correct?
>
> Also. Is it supposed that SIGILL can have a hanlder or can be blocked, or
> it should always kill the whole thread group?

A handler would be reasonable for the process.

> I think we need the patch below, assuming that SIGILL should be sent to
> the single thread and it is fine to have a handler for SIGILL.

Thanks; I appreciate the additional code review in any case. I'll look at
the ramifications of the change in more detail when I return from vacation
late next week.

> Oleg.
>
> --- sigprocmask/arch/tile/kernel/hardwall.c~1_sighand 2011-04-06 21:33:42.000000000 +0200
> +++ sigprocmask/arch/tile/kernel/hardwall.c 2011-04-21 20:56:36.000000000 +0200
> @@ -268,12 +268,10 @@ void __kprobes do_hardwall_trap(struct p
> found_processes = 0;
> list_for_each_entry(p, &rect->task_head, thread.hardwall_list) {
> BUG_ON(p->thread.hardwall != rect);
> - if (p->sighand) {
> + if (!(p->flags & PF_EXITING)) {
> found_processes = 1;
> pr_notice("hardwall: killing %d\n", p->pid);
> - spin_lock(&p->sighand->siglock);
> - __group_send_sig_info(info.si_signo, &info, p);
> - spin_unlock(&p->sighand->siglock);
> + do_send_sig_info(info.si_signo, &info, p, false);
> }
> }
> if (!found_processes)
>

--
Chris Metcalf, Tilera Corp.
http://www.tilera.com



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