[PATCH v4 1/3] lsm: introduce new hooks for setting/getting inode fsxattr

[Mickaël Salaün]

On Fri, Mar 21, 2025 at 05:32:25PM -0400, Paul Moore wrote:
> On Mar 21, 2025 Andrey Albershteyn <aalbersh at redhat.com> wrote:
> > 
> > Introduce new hooks for setting and getting filesystem extended
> > attributes on inode (FS_IOC_FSGETXATTR).
> > 
> > Cc: selinux at vger.kernel.org
> > Cc: Paul Moore <paul at paul-moore.com>
> > 
> > Signed-off-by: Andrey Albershteyn <aalbersh at kernel.org>
> > ---
> >  fs/ioctl.c                    |  7 ++++++-
> >  include/linux/lsm_hook_defs.h |  4 ++++
> >  include/linux/security.h      | 16 ++++++++++++++++
> >  security/security.c           | 32 ++++++++++++++++++++++++++++++++
> >  4 files changed, 58 insertions(+), 1 deletion(-)
> 
> Thanks Andrey, one small change below, but otherwise this looks pretty
> good.  If you feel like trying to work up the SELinux implementation but
> need some assitance please let me know, I'll be happy to help :)
> 
> > diff --git a/fs/ioctl.c b/fs/ioctl.c
> > index 638a36be31c14afc66a7fd6eb237d9545e8ad997..4434c97bc5dff5a3e8635e28745cd99404ff353e 100644
> > --- a/fs/ioctl.c
> > +++ b/fs/ioctl.c
> > @@ -525,10 +525,15 @@ EXPORT_SYMBOL(fileattr_fill_flags);
> >  int vfs_fileattr_get(struct dentry *dentry, struct fileattr *fa)
> >  {
> >  	struct inode *inode = d_inode(dentry);
> > +	int error;
> >  
> >  	if (!inode->i_op->fileattr_get)
> >  		return -ENOIOCTLCMD;
> >  
> > +	error = security_inode_getfsxattr(inode, fa);
> > +	if (error)
> > +		return error;
> > +
> >  	return inode->i_op->fileattr_get(dentry, fa);
> >  }
> >  EXPORT_SYMBOL(vfs_fileattr_get);
> > @@ -692,7 +697,7 @@ int vfs_fileattr_set(struct mnt_idmap *idmap, struct dentry *dentry,
> >  			fa->flags |= old_ma.flags & ~FS_COMMON_FL;
> >  		}
> >  		err = fileattr_set_prepare(inode, &old_ma, fa);
> > -		if (!err)
> > +		if (!err && !security_inode_setfsxattr(inode, fa))
> >  			err = inode->i_op->fileattr_set(idmap, dentry, fa);
> >  	}
> >  	inode_unlock(inode);
> 
> I don't believe we want to hide or otherwise drop the LSM return code as
> that could lead to odd behavior, e.g. returning 0/success despite not
> having executed the fileattr_set operation.

Yes, this should look something like this:

 		err = fileattr_set_prepare(inode, &old_ma, fa);
 		if (err)
 			goto out;
 		err = security_inode_setfsxattr(dentry, fa);
 		if (err)
 			goto out;
 		err = inode->i_op->fileattr_set(idmap, dentry, fa);
 		if (err)
 			goto out;

> 
> --
> paul-moore.com
>