linux-kernel - Re: [RFC PATCH] procfs: Add file path and size to /proc/<pid>/fdinfo

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Message-ID: <CAC_TJve0iyPU0uKoKOi_qcwgxPkgNKgirBcMJ=oYBqhRC3a_+Q@mail.gmail.com>
Date:   Thu, 19 May 2022 21:01:39 -0700
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Ioannis Ilkos <ilkos@...gle.com>,
        "T.J. Mercier" <tjmercier@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Jonathan Corbet <corbet@....net>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Anton Mitterer <mail@...istoph.anton.mitterer.name>,
        Mike Rapoport <rppt@...nel.org>,
        Colin Cross <ccross@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        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>
Subject: Re: [RFC PATCH] procfs: Add file path and size to /proc/<pid>/fdinfo

On Thu, May 19, 2022 at 6:50 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, May 19, 2022 at 02:40:15PM -0700, Kalesh Singh wrote:
> > [...]
> > +     seq_file_path(m, file, "\n");
> > +     seq_putc(m, '\n');
> >
> >       /* show_fd_locks() never deferences files so a stale value is safe */
> >       show_fd_locks(m, file, files);
>
> This comment implies "file" might be stale? Does that mean anything for
> the above seq_file_path()?

Hi Kees.

Thanks for taking a look. The comment above says the "files" pointer
can be stale. It doesn't affect our use of "file" here. seq_show()
takes the reference with get_file() so "file" wouldn't be destroyed
from under us.

Thanks,
Kalesh
>
> --
> Kees Cook