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Date:   Fri, 8 Jan 2021 18:19:22 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Edgar Arriaga GarcĂ­a <edgararriaga@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        linux-mm <linux-mm@...ck.org>, selinux@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH 1/1] mm/madvise: replace ptrace attach requirement for process_madvise

On Fri, Jan 8, 2021 at 5:02 PM David Rientjes <rientjes@...gle.com> wrote:
>
> On Fri, 8 Jan 2021, Suren Baghdasaryan wrote:
>
> > > > @@ -1197,12 +1197,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
> > > >               goto release_task;
> > > >       }
> > > >
> > > > -     mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
> > > > +     /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */
> > > > +     mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
> > > >       if (IS_ERR_OR_NULL(mm)) {
> > > >               ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
> > > >               goto release_task;
> > > >       }
> > > >
> > > > +     /*
> > > > +      * Require CAP_SYS_NICE for influencing process performance. Note that
> > > > +      * only non-destructive hints are currently supported.
> > > > +      */
> > > > +     if (!capable(CAP_SYS_NICE)) {
> > > > +             ret = -EPERM;
> > > > +             goto release_task;
> > >
> > > mmput?
> >
> > Ouch! Thanks for pointing it out! Will include in the next respin.
> >
>
> With the fix, feel free to add:
>
>         Acked-by: David Rientjes <rientjes@...gle.com>

Thanks! Will post a new version with the fix on Monday.

>
> Thanks Suren!

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