linux-kernel - Re: [PATCH v7 2/9] pidfd: Add missing sock updates for pidfd

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Message-ID: <202007091534.382887A@keescook>
Date:   Thu, 9 Jul 2020 15:35:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Sargun Dhillon <sargun@...gun.me>,
        Christian Brauner <christian@...uner.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Laight <David.Laight@...lab.com>,
        Christoph Hellwig <hch@....de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Aleksa Sarai <cyphar@...har.com>,
        Matt Denton <mpdenton@...gle.com>,
        Chris Palmer <palmer@...gle.com>,
        Robert Sesek <rsesek@...gle.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, Shuah Khan <shuah@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v7 2/9] pidfd: Add missing sock updates for pidfd_getfd()

On Thu, Jul 09, 2020 at 10:00:42PM +0200, Jann Horn wrote:
> On Thu, Jul 9, 2020 at 8:26 PM Kees Cook <keescook@...omium.org> wrote:
> > The sock counting (sock_update_netprioidx() and sock_update_classid())
> > was missing from pidfd's implementation of received fd installation. Add
> > a call to the new __receive_sock() helper.
> [...]
> > diff --git a/kernel/pid.c b/kernel/pid.c
> [...]
> > @@ -642,10 +643,12 @@ static int pidfd_getfd(struct pid *pid, int fd)
> >         }
> >
> >         ret = get_unused_fd_flags(O_CLOEXEC);
> > -       if (ret < 0)
> > +       if (ret < 0) {
> >                 fput(file);
> > -       else
> > +       } else {
> >                 fd_install(ret, file);
> > +               __receive_sock(file);
> > +       }
> 
> __receive_sock() has to be before fd_install(), otherwise `file` can
> be a dangling pointer.

I've swapped the order now and double-checked the other uses. Everything
else seems fine.

-- 
Kees Cook