From: Christian Brauner <christian.brauner@ubuntu.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: linux-kernel@vger.kernel.org,
Christian Brauner <christian@brauner.io>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>,
Sargun Dhillon <sargun@sargun.me>,
Aleksa Sarai <cyphar@cyphar.com>,
linux-kselftest@vger.kernel.org,
Josh Triplett <josh@joshtriplett.org>,
Jens Axboe <axboe@kernel.dk>,
linux-api@vger.kernel.org
Subject: Re: [PATCH v2 1/4] pidfd: support PIDFD_NONBLOCK in pidfd_open()
Date: Thu, 3 Sep 2020 17:25:29 +0200 [thread overview]
Message-ID: <20200903152529.llgvshvvoymwealz@wittgenstein> (raw)
In-Reply-To: <20200903145808.GK4386@redhat.com>
On Thu, Sep 03, 2020 at 04:58:09PM +0200, Oleg Nesterov wrote:
> Christian, off-topic question...
>
> On 09/02, Christian Brauner wrote:
> >
> > -static int pidfd_create(struct pid *pid)
> > +static int pidfd_create(struct pid *pid, unsigned int flags)
> > {
> > int fd;
> >
> > fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid),
> > - O_RDWR | O_CLOEXEC);
> > + flags | O_RDWR | O_CLOEXEC);
>
> I just noticed this comment above pidfd_create:
>
> * Note, that this function can only be called after the fd table has
> * been unshared to avoid leaking the pidfd to the new process.
>
> what does it mean?
>
> Of course, if fd table is shared then pidfd can "leak" to another process,
> but this is true for any file and sys_pidfd_open() doesn't do any check?
It's the same comment we added in kernel/fork.c to make callers aware
that they can leak a pidfd to another process unintentionally. Sure,
this is true of any fd but since pidfds were a new type of handle and on
another process at that we felt that this was important to spell out. The
"can only" should've arguably been "should probably".
>
>
>
> In fact I think this helper buys nothing but adds the unnecessary get/put_pid,
> we can kill it and change pidfd_open() to do
>
> SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
> {
> int fd;
> struct pid *p;
>
> if (flags & ~PIDFD_NONBLOCK)
> return -EINVAL;
>
> if (pid <= 0)
> return -EINVAL;
>
> p = find_get_pid(pid);
> if (!p)
> return -ESRCH;
>
> fd = -EINVAL;
> if (pid_has_task(p, PIDTYPE_TGID)) {
> fd = anon_inode_getfd("[pidfd]", &pidfd_fops, pid,
> flags | O_RDWR | O_CLOEXEC);
> }
> if (fd < 0)
> put_pid(p);
> return fd;
> }
Sure, I'd totally take a patch like that!
>
> but this is cosmetic and off-topic too.
No, much appreciated. Good-looking code is important. :)
Christian
next prev parent reply other threads:[~2020-09-03 15:25 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-02 10:21 [PATCH v2 0/4] Support non-blocking pidfds Christian Brauner
2020-09-02 10:21 ` [PATCH v2 1/4] pidfd: support PIDFD_NONBLOCK in pidfd_open() Christian Brauner
2020-09-03 14:31 ` Oleg Nesterov
2020-09-03 14:58 ` Oleg Nesterov
2020-09-03 15:25 ` Christian Brauner [this message]
2020-09-03 23:50 ` Josh Triplett
2020-09-02 10:21 ` [PATCH v2 2/4] exit: support non-blocking pidfds Christian Brauner
2020-09-03 14:22 ` Oleg Nesterov
2020-09-03 15:38 ` Christian Brauner
2020-09-03 23:54 ` Josh Triplett
2020-09-03 23:56 ` Josh Triplett
2020-09-04 10:29 ` Christian Brauner
2020-09-02 10:21 ` [PATCH v2 3/4] tests: port pidfd_wait to kselftest harness Christian Brauner
2020-09-02 10:21 ` [PATCH v2 4/4] tests: add waitid() tests for non-blocking pidfds Christian Brauner
2020-09-03 23:58 ` [PATCH v2 0/4] Support " Josh Triplett
2020-09-04 10:30 ` Christian Brauner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200903152529.llgvshvvoymwealz@wittgenstein \
--to=christian.brauner@ubuntu.com \
--cc=axboe@kernel.dk \
--cc=christian@brauner.io \
--cc=cyphar@cyphar.com \
--cc=ebiederm@xmission.com \
--cc=josh@joshtriplett.org \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=sargun@sargun.me \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).