linux-hardening - Re: [PATCH 6/9] fs: Introduce file_to

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Date:   Tue, 18 Oct 2022 11:25:02 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian Brauner <brauner@...nel.org>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        John Johansen <john.johansen@...onical.com>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        Mickaël Salaün <mic@...ikod.net>,
        KP Singh <kpsingh@...nel.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 6/9] fs: Introduce file_to_perms() helper

On Tue, Oct 18, 2022 at 04:10:37PM +0200, Christian Brauner wrote:
> On Thu, Oct 13, 2022 at 03:36:51PM -0700, Kees Cook wrote:
> > Extract the logic used by LSM file hooks to be able to reconstruct the
> > access mode permissions from an open.
> > 
> > Cc: John Johansen <john.johansen@...onical.com>
> > Cc: Paul Moore <paul@...l-moore.com>
> > Cc: James Morris <jmorris@...ei.org>
> > Cc: "Serge E. Hallyn" <serge@...lyn.com>
> > Cc: linux-security-module@...r.kernel.org
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> >  include/linux/fs.h               | 22 ++++++++++++++++++++++
> >  security/apparmor/include/file.h | 18 ++++--------------
> >  2 files changed, 26 insertions(+), 14 deletions(-)
> > 
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 9eced4cc286e..814f10d4132e 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -993,6 +993,28 @@ static inline struct file *get_file(struct file *f)
> >  #define get_file_rcu(x) atomic_long_inc_not_zero(&(x)->f_count)
> >  #define file_count(x)	atomic_long_read(&(x)->f_count)
> >  
> > +/* Calculate the basic MAY_* flags needed for a given file. */
> > +static inline u8 file_to_perms(struct file *file)
> 
> As long as there aren't multiple users of this and especially none in
> the vfs proper please don't move this into fs.h. It's overloaded enough
> as it is and we have vague plans on splitting it further in the future.

Sure -- this can live in a security .h file somewhere.

-- 
Kees Cook