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Date: Tue, 8 Sep 2020 08:52:01 -0400
From: Stephen Smalley <stephen.smalley.work@...il.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: Mimi Zohar <zohar@...ux.ibm.com>, linux-kernel <linux-kernel@...r.kernel.org>,
Aleksa Sarai <cyphar@...har.com>, Alexei Starovoitov <ast@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
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LSM List <linux-security-module@...r.kernel.org>,
Linux FS Devel <linux-fsdevel@...r.kernel.org>,
Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
Mickaël Salaün <mic@...ux.microsoft.com>,
John Johansen <john.johansen@...onical.com>
Subject: Re: [RFC PATCH v8 1/3] fs: Introduce AT_INTERPRETED flag for faccessat2(2)
On Tue, Sep 8, 2020 at 8:50 AM Stephen Smalley
<stephen.smalley.work@...il.com> wrote:
>
> On Tue, Sep 8, 2020 at 8:43 AM Mickaël Salaün <mic@...ikod.net> wrote:
> >
> >
> > On 08/09/2020 14:28, Mimi Zohar wrote:
> > > Hi Mickael,
> > >
> > > On Tue, 2020-09-08 at 09:59 +0200, Mickaël Salaün wrote:
> > >> + mode |= MAY_INTERPRETED_EXEC;
> > >> + /*
> > >> + * For compatibility reasons, if the system-wide policy
> > >> + * doesn't enforce file permission checks, then
> > >> + * replaces the execute permission request with a read
> > >> + * permission request.
> > >> + */
> > >> + mode &= ~MAY_EXEC;
> > >> + /* To be executed *by* user space, files must be readable. */
> > >> + mode |= MAY_READ;
> > >
> > > After this change, I'm wondering if it makes sense to add a call to
> > > security_file_permission(). IMA doesn't currently define it, but
> > > could.
> >
> > Yes, that's the idea. We could replace the following inode_permission()
> > with file_permission(). I'm not sure how this will impact other LSMs though.
>
> They are not equivalent at least as far as SELinux is concerned.
> security_file_permission() was only to be used to revalidate
> read/write permissions previously checked at file open to support
> policy changes and file or process label changes. We'd have to modify
> the SELinux hook if we wanted to have it check execute access even if
> nothing has changed since open time.
Also Smack doesn't appear to implement file_permission at all, so it
would skip Smack checking.
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