linux-kernel - Re: [PATCH] SELinux: Always allow FIOCLEX and FIONCLEX

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Message-ID: <CAHC9VhSjTqT-4TMxBnQOQHkj+djONihfeoPVyy1egrZY2t10XA@mail.gmail.com>
Date:   Tue, 25 Jan 2022 17:27:02 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Demi Marie Obenour <demiobenour@...il.com>
Cc:     Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] SELinux: Always allow FIOCLEX and FIONCLEX

On Tue, Jan 25, 2022 at 4:34 PM Demi Marie Obenour
<demiobenour@...il.com> wrote:
>
> These ioctls are equivalent to fcntl(fd, F_SETFD, flags), which SELinux
> always allows too.  Furthermore, a failed FIOCLEX could result in a file
> descriptor being leaked to a process that should not have access to it.
>
> Signed-off-by: Demi Marie Obenour <demiobenour@...il.com>
> ---
>  security/selinux/hooks.c | 5 +++++
>  1 file changed, 5 insertions(+)

I'm not convinced that these two ioctls should be exempt from SELinux
policy control, can you explain why allowing these ioctls with the
file:ioctl permission is not sufficient for your use case?  Is it a
matter of granularity?

> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 5b6895e4fc29..8f3b2f15c1f3 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3728,6 +3728,11 @@ static int selinux_file_ioctl(struct file *file, unsigned int cmd,
>                 error = file_has_perm(cred, file, FILE__GETATTR);
>                 break;
>
> +       /* must always succeed */
> +       case FIOCLEX:
> +       case FIONCLEX:
> +               break;
> +
>         case FS_IOC_SETFLAGS:
>         case FS_IOC_SETVERSION:
>                 error = file_has_perm(cred, file, FILE__SETATTR);

--
paul-moore.com