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Message-ID: <CAHk-=wiGNSQCA8TYa1Akp0_GRpe=ELKDPkDX5nzM5R=oDy1U+Q@mail.gmail.com>
Date: Sat, 25 Jan 2020 10:45:25 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Alexey Gladkov <gladkov.alexey@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linux API <linux-api@...r.kernel.org>,
Linux FS Devel <linux-fsdevel@...r.kernel.org>,
Linux Security Module <linux-security-module@...r.kernel.org>,
Akinobu Mita <akinobu.mita@...il.com>, Alexander Viro <viro@...iv.linux.org.uk>,
Alexey Dobriyan <adobriyan@...il.com>, Andrew Morton <akpm@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>, Daniel Micay <danielmicay@...il.com>,
Djalal Harouni <tixxdz@...il.com>, "Dmitry V . Levin" <ldv@...linux.org>,
"Eric W . Biederman" <ebiederm@...ssion.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Ingo Molnar <mingo@...nel.org>, "J . Bruce Fields" <bfields@...ldses.org>,
Jeff Layton <jlayton@...chiereds.net>, Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>, Oleg Nesterov <oleg@...hat.com>,
Solar Designer <solar@...nwall.com>, Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v7 07/11] proc: flush task dcache entries from all procfs instances
On Sat, Jan 25, 2020 at 5:06 AM Alexey Gladkov <gladkov.alexey@...il.com> wrote:
>
> This allows to flush dcache entries of a task on multiple procfs mounts
> per pid namespace.
>From a quick read-through, this is the only one I really react negatively to.
The locking looks odd. It only seems to protect the new proc_mounts
list, but then it's a whole big rwsem, and it's taken over all of
proc_flush_task_mnt(), and the locking is exported to all over as a
result of that - including the dummy functions for "there is no proc"
case.
And proc_flush_task_mnt() itself should need no locking over any of
it, so it's all just for the silly looping over the list.
So
(a) this looks fishy and feels wrong - I get a very strong feeling
that the locking is wrong to begin with, and could/should have been
done differently
(b) all the locking should have been internal to /proc, and those
wrappers shouldn't exist in a common header file (and certainly not
for the non-proc case).
Yes, (a) is just a feeling, and I don't have any great suggestions.
Maybe make it an RCU list and use a spinlock for updating it?
But (b) is pretty much a non-starter in this form. Those wrappers
shouldn't be in a globally exported core header file. No way.
Linus
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