linux-kernel - Re: [PATCH 2/4] fs/notify: don't put file handle buffer on stack.

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Message-ID: <CAOQ4uxhT_=Ot8tuCr6wAOTOZGhyR52CsqoCgJJ2Za_WUGRauvg@mail.gmail.com>
Date:   Mon, 11 Dec 2017 08:47:40 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     NeilBrown <neilb@...e.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Lennart Poettering <lennart@...ttering.net>,
        Pavel Emelyanov <xemul@...tuozzo.com>
Subject: Re: [PATCH 2/4] fs/notify: don't put file handle buffer on stack.

On Mon, Dec 11, 2017 at 8:04 AM, NeilBrown <neilb@...e.com> wrote:
> A file handle buffer is not tiny, and could need to be larger in future,
> so it isn't safe to allocate one on the stack.  Instead, we need to
> kmalloc().
>
> There is no way to return an error status from a ->show_fdinfo()
> function, so if the kmalloc fails, we silently exclude the filehandle
> from the output.  As it is at the end of line, this shouldn't
> upset parsing too much.

I think that is a bold assumption to make about parsers ;)
Anyway, the second reasoning is stronger, so may as well drop this one.
There is probably a single userspace user for this which is CRIU,
for which this fdinfo file handle was added, so you could possibly say
that this change does not upset this user (?).

> In any case, it can only fail when the
> process is being killed by the OOM killer, so the file will never
> be parsed anyway.
>
> Signed-off-by: NeilBrown <neilb@...e.com>