linux-kernel - Re: [PATCH v2 12/25] selinux: add hooks for fscaps operations

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Date: Wed, 21 Feb 2024 19:19:07 -0500
From: Paul Moore <paul@...l-moore.com>
To: "Seth Forshee (DigitalOcean)" <sforshee@...nel.org>
Cc: Christian Brauner <brauner@...nel.org>, Serge Hallyn <serge@...lyn.com>, Eric Paris <eparis@...hat.com>, 
	James Morris <jmorris@...ei.org>, Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
	Stephen Smalley <stephen.smalley.work@...il.com>, Ondrej Mosnacek <omosnace@...hat.com>, 
	Casey Schaufler <casey@...aufler-ca.com>, Mimi Zohar <zohar@...ux.ibm.com>, 
	Roberto Sassu <roberto.sassu@...wei.com>, Dmitry Kasatkin <dmitry.kasatkin@...il.com>, 
	Eric Snowberg <eric.snowberg@...cle.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, 
	Jonathan Corbet <corbet@....net>, Miklos Szeredi <miklos@...redi.hu>, Amir Goldstein <amir73il@...il.com>, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-security-module@...r.kernel.org, audit@...r.kernel.org, 
	selinux@...r.kernel.org, linux-integrity@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-unionfs@...r.kernel.org
Subject: Re: [PATCH v2 12/25] selinux: add hooks for fscaps operations

On Wed, Feb 21, 2024 at 7:10 PM Seth Forshee (DigitalOcean)
<sforshee@...nel.org> wrote:
> On Wed, Feb 21, 2024 at 06:38:33PM -0500, Paul Moore wrote:
> > On Wed, Feb 21, 2024 at 4:25 PM Seth Forshee (DigitalOcean)
> > <sforshee@...nel.org> wrote:
> > >
> > > Add hooks for set/get/remove fscaps operations which perform the same
> > > checks as the xattr hooks would have done for XATTR_NAME_CAPS.
> > >
> > > Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@...nel.org>
> > > ---
> > >  security/selinux/hooks.c | 26 ++++++++++++++++++++++++++
> > >  1 file changed, 26 insertions(+)
> > >
> > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > > index a6bf90ace84c..da129a387b34 100644
> > > --- a/security/selinux/hooks.c
> > > +++ b/security/selinux/hooks.c
> > > @@ -3367,6 +3367,29 @@ static int selinux_inode_removexattr(struct mnt_idmap *idmap,
> > >         return -EACCES;
> > >  }
> > >
> > > +static int selinux_inode_set_fscaps(struct mnt_idmap *idmap,
> > > +                                   struct dentry *dentry,
> > > +                                   const struct vfs_caps *caps, int flags)
> > > +{
> > > +       return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
> > > +}
> >
> > The selinux_inode_setxattr() code also has a cap_inode_setxattr()
> > check which is missing here.  Unless you are handling this somewhere
> > else, I would expect the function above to look similar to
> > selinux_inode_remove_fscaps(), but obviously tweaked for setting the
> > fscaps and not removing them.
>
> Right, but cap_inode_setxattr() doesn't do anything for fscaps, so I
> omitted the call. Unless you think the call should be included in case
> cap_inode_setxattr() changes in the future, which is a reasonable
> position.

Fair enough, but I'd be a lot happier if you included the call in case
something changes in the future.  I worry that omitting the call would
make it easier for us to forget about this if/when things change and
suddenly we have a security issue.  If you are morally opposed to
that, at the very least put a comment in selinux_inode_set_fscaps()
about this so we know who to yell at in the future ;)

-- 
paul-moore.com