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Message-ID: <b63caccf-11d1-2c98-71b0-36898e28b0f4@digikod.net>
Date: Fri, 1 May 2020 16:17:54 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: James Morris <jmorris@...ei.org>
Cc: linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>,
Alexei Starovoitov <ast@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
Andy Lutomirski <luto@...nel.org>, Christian Heimes <christian@...hon.org>,
Daniel Borkmann <daniel@...earbox.net>,
Deven Bowers <deven.desai@...ux.microsoft.com>,
Eric Chiang <ericchiang@...gle.com>, Florian Weimer <fweimer@...hat.com>,
Jan Kara <jack@...e.cz>, Jann Horn <jannh@...gle.com>,
Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>,
Matthew Garrett <mjg59@...gle.com>, Matthew Wilcox <willy@...radead.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Mickaël Salaün <mickael.salaun@....gouv.fr>,
Mimi Zohar <zohar@...ux.ibm.com>,
Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
Scott Shell <scottsh@...rosoft.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Shuah Khan <shuah@...nel.org>, Steve Dower <steve.dower@...hon.org>,
Steve Grubb <sgrubb@...hat.com>,
Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
Vincent Strubel <vincent.strubel@....gouv.fr>,
kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
linux-security-module@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] fs: Add a MAY_EXECMOUNT flag to infer the noexec
mount property
On 01/05/2020 06:02, James Morris wrote:
> On Tue, 28 Apr 2020, Mickaël Salaün wrote:
>
>> An LSM doesn't get path information related to an access request to open
>> an inode. This new (internal) MAY_EXECMOUNT flag enables an LSM to
>> check if the underlying mount point of an inode is marked as executable.
>> This is useful to implement a security policy taking advantage of the
>> noexec mount option.
>>
>> This flag is set according to path_noexec(), which checks if a mount
>> point is mounted with MNT_NOEXEC or if the underlying superblock is
>> SB_I_NOEXEC.
>>
>> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
>> Reviewed-by: Philippe Trébuchet <philippe.trebuchet@....gouv.fr>
>> Reviewed-by: Thibaut Sautereau <thibaut.sautereau@....gouv.fr>
>> Cc: Aleksa Sarai <cyphar@...har.com>
>> Cc: Al Viro <viro@...iv.linux.org.uk>
>> Cc: Kees Cook <keescook@...omium.org>
>
> Are there any existing LSMs which plan to use this aspect?
This commit message was initially for the first version of O_MAYEXEC,
which extended Yama. The current enforcement implementation is now
directly in the FS subsystem (as requested by Kees Cook). However, this
MAY_EXECMOUNT flag is still used by the current FS implementation and it
could still be useful for LSMs.
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