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From:   Kalesh Singh <kaleshsingh@google.com>
Date:   Wed, 3 Feb 2021 15:49:27 -0500
Message-ID: <CAC_TJvdUN27PsjnehS03UQB=LdQUo9KJK=q1bgxJnZh2FJzXjw@mail.gmail.com>
Subject: Re: [PATCH 0/2] Allow reading process DMA buf stats from fdinfo
Cc:     Jann Horn <jannh@google.com>,
        Jeffrey Vander Stoep <jeffv@google.com>,
        Kees Cook <keescook@chromium.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Minchan Kim <minchan@kernel.org>,
        Hridya Valsaraju <hridya@google.com>,
        "Cc: Android Kernel" <kernel-team@android.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexey Gladkov <gladkov.alexey@gmail.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        Michel Lespinasse <walken@google.com>,
        Bernd Edlinger <bernd.edlinger@hotmail.de>,
        Andrei Vagin <avagin@gmail.com>,
        Yafang Shao <laoar.shao@gmail.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        DRI mailing list <dri-devel@lists.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@lists.linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
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On Thu, Jan 28, 2021 at 1:24 PM Kalesh Singh <kaleshsingh@google.com> wrote=
:
>
> Android captures per-process system memory state when certain low memory
> events (e.g a foreground app kill) occur, to identify potential memory
> hoggers. In order to measure how much memory a process actually consumes,
> it is necessary to include the DMA buffer sizes for that process in the
> memory accounting. Since the handle to DMA buffers are raw FDs, it is
> important to be able to identify which processes have FD references to
> a DMA buffer.
>
> Currently, DMA buffer FDs can be accounted using /proc/<pid>/fd/* and
> /proc/<pid>/fdinfo -- both are only readable by the process owner,
> as follows:
>   1. Do a readlink on each FD.
>   2. If the target path begins with "/dmabuf", then the FD is a dmabuf FD=
.
>   3. stat the file to get the dmabuf inode number.
>   4. Read/ proc/<pid>/fdinfo/<fd>, to get the DMA buffer size.
>
> Accessing other processes=E2=80=99 fdinfo requires root privileges. This =
limits
> the use of the interface to debugging environments and is not suitable
> for production builds.  Granting root privileges even to a system process
> increases the attack surface and is highly undesirable.
>
> This series proposes making the requirement to read fdinfo less strict
> with PTRACE_MODE_READ.
>

Hi everyone,

I will send v2 of this patch series. Please let me know if you have
any other comments or feedback, that should be addressed in the new
version.

Thanks,
Kalesh

> Kalesh Singh (2):
>   procfs: Allow reading fdinfo with PTRACE_MODE_READ
>   dmabuf: Add dmabuf inode no to fdinfo
>
>  drivers/dma-buf/dma-buf.c |  1 +
>  fs/proc/base.c            |  4 ++--
>  fs/proc/fd.c              | 15 ++++++++++++++-
>  3 files changed, 17 insertions(+), 3 deletions(-)
>
> --
> 2.30.0.365.g02bc693789-goog
>