Re: [PATCH v9 12/25] security: Introduce file_post_open hook

[Roberto Sassu]

On Fri, 2024-02-09 at 12:34 +0100, Christian Brauner wrote:
> 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@xxxxxxxxxx>
> > > > 
> > > > 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@xxxxxxxxxx>
> > > > Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> > > > Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> > > > Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> > > > ---
> > > >  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.

Actually it doesn't. I added code to artifically create the situation
(to see what happens if a new LSM does that).

Roberto