Oleg Nesterov <o...@redhat.com> writes:
> On 08/13, Eric W. Biederman wrote:
>>
>> Oleg Nesterov <o...@redhat.com> writes:
>>
>> > On 08/12, Eric W. Biederman wrote:
>> >>
>> >> + if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
>> >> + if (atomic_read(¤t->sighand->count) > 1)
>> >> + return -EINVAL;
>> >> + }
>> >
>> > I am still not sure we want this... please the the previous email.
>>
>> Reading your other email I did not see why you thought this check was
>> unnecessary.
>>
>> > But perhaps I missed something.
>>
>> In short:
>> clone(VM) --> mm_users > 1 && sighand_struct->count == 1
>> followed by:
>> unshare(SIGHAND)
>> the unshare should succeed.
>>
>> Meanwhile:
>> clone(VM|SIGHAND) --> mm_users > 1 && sighand_struct->count > 1
>> followed by:
>> unshare(SIGHAND)
>> the unshare should fail.
>
> Yes, yes, yes.
>
> But once again, I meant we can remove this sighand->count check
> if unshare(SIGHAND) checks current_is_single_threaded(). That is
> why I suggested to do
>
> if (unshare_flags & CLONE_SIGHAND)
> unshare_flags |= CLONE_VM;
>
> in sys_unshare(), or change check_unshare_flags() to check
> "unshare_flags & (CLONE_VM | CLONE_SIGHAND)" before
> current_is_single_threaded().
See the two cases above that change to unshare_flags will make
unshare(SIGHAND) fail when sighand_struct->count == 1.
Which is fundamentally wrong.
> Damn. And this discussion makes me think that another cleanup makes
> sense too. Can't we move all these unshare_flags manipulations into
> check_unshare_flags? So that sys_unshare() will only do
>
> err = check_unshare_flags(&unshare_flags);
>
> and the reader of this code won't need to read 2 functions to understand
> whats going on.
Eric
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