linux-kernel - Re: [PATCH 0/2] Allow reading process DMA buf stats from fdinfo

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Message-ID: <CAC_TJvdUN27PsjnehS03UQB=LdQUo9KJK=q1bgxJnZh2FJzXjw@mail.gmail.com>
Date:   Wed, 3 Feb 2021 15:49:27 -0500
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Jann Horn <jannh@...gle.com>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Michel Lespinasse <walken@...gle.com>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        Andrei Vagin <avagin@...il.com>,
        Yafang Shao <laoar.shao@...il.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Allow reading process DMA buf stats from fdinfo

On Thu, Jan 28, 2021 at 1:24 PM Kalesh Singh <kaleshsingh@...gle.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’ 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
>