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SubjectRe: [PATCH] signal: don't silently convert SI_USER signals to non-current pidfd
On Mon, Apr 08, 2019 at 03:13:16PM +0200, Oleg Nesterov wrote:
> On 03/30, Jann Horn wrote:
> >
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -3605,16 +3605,11 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
> > if (unlikely(sig != kinfo.si_signo))
> > goto err;
> >
> > + /* Only allow sending arbitrary signals to yourself. */
> > + ret = -EPERM;
> > if ((task_pid(current) != pid) &&
> > - (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL)) {
> > - /* Only allow sending arbitrary signals to yourself. */
> > - ret = -EPERM;
> > - if (kinfo.si_code != SI_USER)
> > - goto err;
> > -
> > - /* Turn this into a regular kill signal. */
> > - prepare_kill_siginfo(sig, &kinfo);
> > - }
> > + (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
> > + goto err;
>
> ACK.
>

Sorry Oleg. I missed that message somehow.
>
> but perhaps it should always fail, even if task_pid(current) == pid.
>
> sys_rt_sigqueueinfo() allows to send any siginfo to yourself, but this is only needed
> for checkpoint/restart.

Yes, that's why this was added. I would leave it in exactly because of
checkpoint/restart. I have sympathies for "this [...] project by various
mad Russians" [1] and it doesn't really hurt us. :)

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=099469502f62fbe0d7e4f0b83a2f22538367f734

Christian

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