linux-kernel - Re: [PATCH v5 13/23] security: Introduce file_pre_free

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Date:   Thu, 16 Nov 2023 10:46:24 +0100
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     Paul Moore <paul@...l-moore.com>, viro@...iv.linux.org.uk,
        brauner@...nel.org, chuck.lever@...cle.com, jlayton@...nel.org,
        neilb@...e.de, kolga@...app.com, Dai.Ngo@...cle.com,
        tom@...pey.com, jmorris@...ei.org, serge@...lyn.com,
        zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
        dhowells@...hat.com, jarkko@...nel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        casey@...aufler-ca.com, mic@...ikod.net
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        selinux@...r.kernel.org, Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v5 13/23] security: Introduce file_pre_free_security hook

On Wed, 2023-11-15 at 23:33 -0500, Paul Moore wrote:
> On Nov  7, 2023 Roberto Sassu <roberto.sassu@...weicloud.com> wrote:
> > 
> > In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> > the file_pre_free_security hook.
> > 
> > IMA calculates at file close the new digest of the file content and writes
> > it to security.ima, so that appraisal at next file access succeeds.
> > 
> > LSMs could also take some action before the last reference of a file is
> > released.
> > 
> > The new hook cannot return an error and cannot cause the operation to be
> > reverted.
> > 
> > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> > Acked-by: Casey Schaufler <casey@...aufler-ca.com>
> > Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
> > ---
> >  fs/file_table.c               |  1 +
> >  include/linux/lsm_hook_defs.h |  1 +
> >  include/linux/security.h      |  4 ++++
> >  security/security.c           | 11 +++++++++++
> >  4 files changed, 17 insertions(+)
> > 
> > diff --git a/fs/file_table.c b/fs/file_table.c
> > index de4a2915bfd4..64ed74555e64 100644
> > --- a/fs/file_table.c
> > +++ b/fs/file_table.c
> > @@ -385,6 +385,7 @@ static void __fput(struct file *file)
> >  	eventpoll_release(file);
> >  	locks_remove_file(file);
> >  
> > +	security_file_pre_free(file);
> 
> I worry that security_file_pre_free() is a misleading name as "free"
> tends to imply memory management tasks, which isn't the main focus of
> this hook.  What do you think of security_file_release() or
> security_file_put() instead?

security_file_release() would be fine for me.

Thanks

Roberto

> >  	ima_file_free(file);
> >  	if (unlikely(file->f_flags & FASYNC)) {
> >  		if (file->f_op->fasync)
> 
> --
> paul-moore.com