From: Christoph Hellwig <hch@lst.de>
To: Ondrej Mosnacek <omosnace@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, Ian Kent <raven@themaw.net>,
autofs@vger.kernel.org,
Linux Security Module list
<linux-security-module@vger.kernel.org>,
SElinux list <selinux@vger.kernel.org>,
Zdenek Pytela <zpytela@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: Commit 13c164b1a186 - regression for LSMs/SELinux?
Date: Mon, 21 Sep 2020 18:09:22 +0200 [thread overview]
Message-ID: <20200921160922.GA23870@lst.de> (raw)
In-Reply-To: <CAFqZXNsoXr1eA4C8==Nvujs5ONpRnuSqaOQQ0n78R=Dbm-EFGA@mail.gmail.com>
[adding Linus and Al]
On Mon, Sep 21, 2020 at 04:51:35PM +0200, Ondrej Mosnacek wrote:
> Hi folks,
>
> It seems that after commit 13c164b1a186 ("autofs: switch to
> kernel_write") there is now an extra LSM permission required (for the
> current task to write to the automount pipe) for processes accessing
> some yet-to-to-be mounted directory on which an autofs mount is set
> up. The call chain is:
> [...]
> autofs_wait() ->
> autofs_notify_daemon() ->
> autofs_write() ->
> kernel_write() ->
> rw_verify_area() ->
> security_file_permission()
>
> The bug report that led me to this commit is at [1].
>
> Technically, this is a regression for LSM users, since this is a
> kernel-internal operation and an LSM permission for the current task
> shouldn't be required. Can this patch be reverted? Perhaps
> __kernel_{read|write}() could instead be renamed to kernel_*_nocheck()
> so that the name is more descriptive?
So we obviously should not break existing user space and need to fix
this ASAP. The trivial "fix" would be to export __kernel_write again
and switch autofs to use it. The other option would be a FMODE flag
to bypass security checks, only to be set if the callers ensures
they've been valided (i.e. in autofs_prepare_pipe).
Any opinions?
next prev parent reply other threads:[~2020-09-21 16:09 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-21 14:51 Commit 13c164b1a186 - regression for LSMs/SELinux? Ondrej Mosnacek
2020-09-21 16:09 ` Christoph Hellwig [this message]
2020-09-21 16:27 ` Linus Torvalds
2020-09-21 16:30 ` Al Viro
2020-09-22 0:30 ` Ian Kent
2020-09-22 1:35 ` Ian Kent
2020-09-22 7:33 ` Ondrej Mosnacek
2020-09-22 12:29 ` Stephen Smalley
2020-09-23 1:55 ` Ian Kent
2020-09-24 8:36 ` Ondrej Mosnacek
2020-09-24 9:47 ` Ian Kent
2020-09-24 14:16 ` Stephen Smalley
2020-09-25 3:37 ` Ian Kent
2020-09-25 3:44 ` Ian Kent
2020-09-25 13:37 ` Ondrej Mosnacek
2020-09-25 17:38 ` Linus Torvalds
2020-09-27 3:07 ` Ian Kent
2020-09-29 12:16 ` Ondrej Mosnacek
2020-09-29 17:23 ` Linus Torvalds
2020-09-29 18:00 ` Christoph Hellwig
2020-09-30 5:50 ` Ian Kent
2020-09-30 10:39 ` Ian Kent
2020-09-30 5:42 ` Ian Kent
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