Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210108205857.1471269-1-surenb@google.com> <X/jZibYD1B42D+r7@google.com>
 <CAJuCfpHa3XHVEjNBDHJNo3RBWGdLnXsgZH9wyiGLqj655GwE2w@mail.gmail.com> <db29d560-45d9-1eb3-60d0-8d6153ac7193@google.com>
In-Reply-To: <db29d560-45d9-1eb3-60d0-8d6153ac7193@google.com>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Fri, 8 Jan 2021 18:19:22 -0800
Message-ID: <CAJuCfpE3QR-8Lm_0cnCFQsDiU2Ui87E6ARQ+ScQuDZ1TNfm-tg@mail.gmail.com>
Subject: Re: [PATCH 1/1] mm/madvise: replace ptrace attach requirement for process_madvise
To:     David Rientjes <rientjes@google.com>
Cc:     Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Jeffrey Vander Stoep <jeffv@google.com>,
        Michal Hocko <mhocko@suse.com>,
        Shakeel Butt <shakeelb@google.com>,
        =?UTF-8?Q?Edgar_Arriaga_Garc=C3=ADa?= <edgararriaga@google.com>,
        Tim Murray <timmurray@google.com>,
        linux-mm <linux-mm@kvack.org>, selinux@vger.kernel.org,
        Linux API <linux-api@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kernel-team <kernel-team@android.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Jan 8, 2021 at 5:02 PM David Rientjes <rientjes@google.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@google.com>

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

>
> Thanks Suren!