From: Jann Horn <jannh@google.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Linux API <linux-api@vger.kernel.org>,
Oleksandr Natalenko <oleksandr@redhat.com>,
Suren Baghdasaryan <surenb@google.com>,
Tim Murray <timmurray@google.com>,
Daniel Colascione <dancol@google.com>,
Sandeep Patil <sspatil@google.com>,
Sonny Rao <sonnyrao@google.com>,
Brian Geffon <bgeffon@google.com>, Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Shakeel Butt <shakeelb@google.com>,
John Dias <joaodias@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>
Subject: Re: [PATCH v4 2/8] mm: introduce external memory hinting API
Date: Thu, 13 Feb 2020 15:08:59 +0100 [thread overview]
Message-ID: <CAG48ez27=pwm5m_N_988xT1huO7g7h6arTQL44zev6TD-h-7Tg@mail.gmail.com> (raw)
In-Reply-To: <20200212233946.246210-3-minchan@kernel.org>
On Thu, Feb 13, 2020 at 12:40 AM Minchan Kim <minchan@kernel.org> wrote:
> To solve the issue, this patch introduces a new syscall process_madvise(2).
> It uses pidfd of an external process to give the hint.
[...]
> + mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
> + if (IS_ERR_OR_NULL(mm)) {
> + ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
> + goto release_task;
> + }
> +
> + ret = do_madvise(task, start, len_in, behavior);
When you're accessing another task, you should ensure that the other
task doesn't gain new privileges by executing a setuid binary in the
middle of being accessed. mm_access() does that for you; it holds the
->cred_guard_mutex while it is looking up the task's ->mm and doing
the security check. mm_access() then returns you an mm pointer that
you're allowed to access without worrying about such things; an
mm_struct never gains privileges, since a setuid execution creates a
fresh mm_struct. However, the task may still execute setuid binaries
and such things.
This means that after you've looked up the mm with mm_access(), you
have to actually *use* that pointer. You're not allowed to simply read
task->mm yourself.
Therefore, I think you should:
- change patch 1/8 ("mm: pass task to do_madvise") to also pass an
mm_struct* to do_madvise (but keep the task_struct* for patch 4/8)
- in this patch, pass the mm_struct* from mm_access() into do_madvise()
- drop patch 3/8 ("mm: validate mm in do_madvise"); it just papers
over a symptom without addressing the underlying problem
next prev parent reply other threads:[~2020-02-13 14:09 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-12 23:39 [PATCH v4 0/8] introduce memory hinting API for external process Minchan Kim
2020-02-12 23:39 ` [PATCH v4 1/8] mm: pass task to do_madvise Minchan Kim
2020-02-13 0:21 ` Alexander Duyck
2020-02-13 17:02 ` Minchan Kim
2020-02-13 17:35 ` Jann Horn
2020-02-12 23:39 ` [PATCH v4 2/8] mm: introduce external memory hinting API Minchan Kim
2020-02-13 14:08 ` Jann Horn [this message]
2020-02-13 16:10 ` Minchan Kim
2020-02-12 23:39 ` [PATCH v4 3/8] mm: validate mm in do_madvise Minchan Kim
2020-02-12 23:39 ` [PATCH v4 4/8] mm: check fatal signal pending of target process Minchan Kim
2020-02-12 23:39 ` [PATCH v4 5/8] mm/madvise: employ mmget_still_valid for write lock Minchan Kim
2020-02-12 23:39 ` [PATCH v4 6/8] mm/madvise: allow KSM hints for remote API Minchan Kim
2020-02-12 23:39 ` [PATCH v4 7/8] pid: export pidfd_get_pid Minchan Kim
2020-02-13 0:25 ` Alexander Duyck
2020-02-13 17:08 ` Minchan Kim
2020-02-12 23:39 ` [PATCH v4 8/8] mm: support both pid and pidfd for process_madvise Minchan Kim
2020-02-13 0:28 ` Alexander Duyck
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