linux-kernel - Re: [PATCH v9 12/25] security: Introduce file_post

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Date: Fri, 9 Feb 2024 12:34:37 +0100
From: Christian Brauner <brauner@...nel.org>
To: Roberto Sassu <roberto.sassu@...weicloud.com>
Cc: viro@...iv.linux.org.uk, chuck.lever@...cle.com, jlayton@...nel.org, 
	neilb@...e.de, kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com, 
	paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com, zohar@...ux.ibm.com, 
	dmitry.kasatkin@...il.com, eric.snowberg@...cle.com, dhowells@...hat.com, jarkko@...nel.org, 
	stephen.smalley.work@...il.com, eparis@...isplace.org, casey@...aufler-ca.com, shuah@...nel.org, 
	mic@...ikod.net, linux-kernel@...r.kernel.org, linux-fsdevel@...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, 
	linux-kselftest@...r.kernel.org, Roberto Sassu <roberto.sassu@...wei.com>, 
	Stefan Berger <stefanb@...ux.ibm.com>
Subject: Re: [PATCH v9 12/25] security: Introduce file_post_open hook

On Fri, Feb 09, 2024 at 11:46:16AM +0100, Roberto Sassu wrote:
> On Fri, 2024-02-09 at 11:12 +0100, Christian Brauner wrote:
> > On Mon, Jan 15, 2024 at 07:17:56PM +0100, Roberto Sassu wrote:
> > > From: Roberto Sassu <roberto.sassu@...wei.com>
> > > 
> > > In preparation to move IMA and EVM to the LSM infrastructure, introduce the
> > > file_post_open hook. Also, export security_file_post_open() for NFS.
> > > 
> > > Based on policy, IMA calculates the digest of the file content and
> > > extends the TPM with the digest, verifies the file's integrity based on
> > > the digest, and/or includes the file digest in the audit log.
> > > 
> > > LSMs could similarly take action depending on the file content and the
> > > access mask requested with open().
> > > 
> > > The new hook returns a value and can cause the open to be aborted.
> > > 
> > > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> > > Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
> > > Acked-by: Casey Schaufler <casey@...aufler-ca.com>
> > > Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
> > > ---
> > >  fs/namei.c                    |  2 ++
> > >  fs/nfsd/vfs.c                 |  6 ++++++
> > >  include/linux/lsm_hook_defs.h |  1 +
> > >  include/linux/security.h      |  6 ++++++
> > >  security/security.c           | 17 +++++++++++++++++
> > >  5 files changed, 32 insertions(+)
> > > 
> > > diff --git a/fs/namei.c b/fs/namei.c
> > > index 71c13b2990b4..fb93d3e13df6 100644
> > > --- a/fs/namei.c
> > > +++ b/fs/namei.c
> > > @@ -3620,6 +3620,8 @@ static int do_open(struct nameidata *nd,
> > >  	error = may_open(idmap, &nd->path, acc_mode, open_flag);
> > >  	if (!error && !(file->f_mode & FMODE_OPENED))
> > >  		error = vfs_open(&nd->path, file);
> > > +	if (!error)
> > > +		error = security_file_post_open(file, op->acc_mode);
> > 
> > What does it do for O_CREAT? IOW, we managed to create that thing and we
> > managed to open that thing. Can security_file_post_open() and
> > ima_file_check() fail afterwards even for newly created files?
> 
> $ strace touch test-file
> ...
> openat(AT_FDCWD, "test-file", O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 0666) = -1 EPERM (Operation not permitted)

Ah, meh. I was hoping IMA just wouldn't care about this case.