linux-kernel - Re: [PATCH] copy_process(): Move fd_install() out of sighand->siglock critical section

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Message-ID: <YgLr2GEXgz/TxdUA@zeniv-ca.linux.org.uk>
Date:   Tue, 8 Feb 2022 22:16:56 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Waiman Long <longman@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexey Gladkov <legion@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jann Horn <jannh@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] copy_process(): Move fd_install() out of
 sighand->siglock critical section

On Tue, Feb 08, 2022 at 03:59:06PM -0600, Eric W. Biederman wrote:

> The fd is being installed in the fdtable of the parent process,
> and the siglock and tasklist_lock are held to protect the child.
> 
> 
> Further fd_install is exposing the fd to userspace where it can be used
> by the process_madvise and the process_mrelease system calls, from
> anything that shares the fdtable of the parent thread.  Which means it
> needs to be guaranteed that kernel_clone will call wake_up_process
> before it is safe to call fd_install.

You mean "no calling fd_install() until after we are past the last possible
failure exit, by which point we know that wake_up_process() will eventually
be called", hopefully?  If so (as I assumed all along), anything downstream
of
        if (fatal_signal_pending(current)) {
		retval = -EINTR;
		goto bad_fork_cancel_cgroup;
	}

should be fine...