From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Jann Horn <jannh@google.com>
Cc: linux-fsdevel@vger.kernel.org,
kernel list <linux-kernel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
akpm@linuxfoundation.org, avagin@virtuozzo.com,
xemul@virtuozzo.com,
Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
avagin@openvz.org, jbaron@akamai.com,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: [patch v4 resend 2/2] kcmp: Add KCMP_EPOLL_TFD mode to compare epoll target files
Date: Sat, 13 May 2017 01:53:40 +0300 [thread overview]
Message-ID: <20170512225340.GD1881@uranus.lan> (raw)
In-Reply-To: <CAG48ez33xco_cHeaHYg2TOCquosbrAStnHikBDZ89No6c7E0Kg@mail.gmail.com>
On Sat, May 13, 2017 at 12:41:30AM +0200, Jann Horn wrote:
> [resending as plaintext]
>
> I realize that the existing kcmp code has the same issue, but:
>
> Why are you not taking a reference to filp or filp_tgt? This can end up
> performing a comparison between a pointer to a freed struct file and a
> pointer to a struct file that was allocated afterwards, right? So it can
> return a false "is equal" result when the two files aren't actually the same
> if one of the target tasks is running? This looks like it unnecessarily
> exposes information about whether an allocation reuses the memory of
> a previously freed allocation.
It work with unlocked data on purpose for speed sake. Moreover even
if we grap a reference it is valid _only_ during comparision operation,
next we drop ref and it can be easily freed by os. Thus it's up to
a caller to keep references to files/task and other resources used.
Cyrill
next prev parent reply other threads:[~2017-05-12 22:53 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-24 15:39 [patch v4 resend 2/2] kcmp: Add KCMP_EPOLL_TFD mode to compare epoll target files Cyrill Gorcunov
[not found] ` <20170424154423.511592110-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2017-05-12 22:00 ` Andrew Morton
[not found] ` <20170512150018.b931c7f5295dd7484845fcec-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
2017-05-12 22:14 ` Cyrill Gorcunov
2017-05-12 22:41 ` Jann Horn
2017-05-12 22:53 ` Cyrill Gorcunov [this message]
[not found] ` <20170512225340.GD1881-ZmlpmtaulQd+urZeOPWqwQ@public.gmane.org>
2017-05-13 1:45 ` Andrei Vagin
[not found] ` <20170513014508.GA21900-1ViLX0X+lBJGNQ1M2rI3KwRV3xvJKrda@public.gmane.org>
2017-05-13 6:55 ` Cyrill Gorcunov
[not found] ` <20170513065514.GE1881-ZmlpmtaulQd+urZeOPWqwQ@public.gmane.org>
2017-05-13 7:15 ` Cyrill Gorcunov
2017-09-17 16:01 ` [v4,resend,2/2] " Eugene Syromiatnikov
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