linux-kernel - Re: [PATCH v2 1/2] fs: make all new mount api fds cloexec by default

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Message-ID: <9333.1557564029@warthog.procyon.org.uk>
Date:   Sat, 11 May 2019 09:40:29 +0100
From:   David Howells <dhowells@...hat.com>
To:     Christian Brauner <christian@...uner.io>
Cc:     dhowells@...hat.com, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] fs: make all new mount api fds cloexec by default

Christian Brauner <christian@...uner.io> wrote:

> This makes all file descriptors returned from new syscalls of the new mount
> api cloexec by default.
> 
> From a userspace perspective it is rarely the case that fds are supposed to
> be inherited across exec. Having them not cloexec by default forces
> userspace to remember to pass the <SPECIFIC>_CLOEXEC flag along or to
> invoke fcntl() on the fd to prevent leaking it. And leaking the fd is a
> much bigger issue than forgetting to remove the cloexec flag and failing to
> inherit the fd.
> For old fd types we can't break userspace. But for new ones we should
> whenever reasonable make them cloexec by default (Examples of this policy
> are the new seccomp notify fds and also pidfds.). If userspace wants to
> inherit fds across exec they can remove the O_CLOEXEC flag and so opt in to
> inheritance explicitly.
> 
> This patch also has the advantage that we can get rid of all the special
> flags per file descriptor type for the new mount api. In total this lets us
> remove 4 flags:
> - FSMOUNT_CLOEXEC
> - FSOPEN_CLOEXEC
> - FSPICK_CLOEXEC
> - OPEN_TREE_CLOEXEC
> 
> Signed-off-by: Christian Brauner <christian@...uner.io>

Fine by me.

Reviewed-by: David Howells <dhowells@...hat.com>