Re: [RFC][PATCH 4/6][v3] Define siginfo_from_ancestor_ns()

[Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>]

Oleg Nesterov [oleg@redhat.com] wrote:
| On 12/22, Oleg Nesterov wrote:
| >
| > On 12/20, Sukadev Bhattiprolu wrote:
| > >
| > > + * TODO:
| > > + * 	  Making SI_ASYNCIO a kernel signal could make this less hacky.
| > > + */
| > > +#ifdef CONFIG_PID_NS
| > > +static inline int siginfo_from_user(siginfo_t *info)
| > > +{
| > > +	if (!is_si_special(info) && SI_FROMUSER(info) &&
| >
| > OK, if we can trust SI_FROMUSER(), then it is better, i agree.
| 
| Aaah, forgot to mention...
| 
| But could you explain how are you going to fix another problem,
| .si_pid mangling? This was another reason for (yes, ugly, agreed)
| SIG_FROM_USER in .si_signo.

Good point.

I was going through the ->si_pid assignments to try and fix them at
source (like the mqueue patch I sent last week).

The two cases that don't fit the model are sys_kill() and sys_tkill().
For that I was hoping we could use siginfo_from_user() again. i.e

	if (siginfo_from_user())
		masquerade_si_pid()

in the default: case of send_signal(). To be safe, masquerade_si_pid()
could do it only iff si_code is either SI_USER or SI_TKILL.

IOW, with some tweaks, I am trying to see if we can use siginfo_from_user()
in place of the SIG_FROM_USER.