[PATCH 08/16] fs: add vfs_get_fscaps()

[Seth Forshee (DigitalOcean)]

On Fri, Dec 01, 2023 at 06:09:36PM +0100, Christian Brauner wrote:
> On Wed, Nov 29, 2023 at 03:50:26PM -0600, Seth Forshee (DigitalOcean) wrote:
> > Provide a type-safe interface for retrieving filesystem capabilities and
> > a generic implementation suitable for most filesystems. Also add an
> > internal interface, __vfs_get_fscaps(), which skips security checks for
> > later use from the capability code.
> > 
> > Signed-off-by: Seth Forshee (DigitalOcean) <sforshee at kernel.org>
> > ---
> >  fs/xattr.c         | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/fs.h |  4 ++++
> >  2 files changed, 70 insertions(+)
> > 
> > diff --git a/fs/xattr.c b/fs/xattr.c
> > index 09d927603433..3abaf9bef0a5 100644
> > --- a/fs/xattr.c
> > +++ b/fs/xattr.c
> > @@ -181,6 +181,72 @@ xattr_supports_user_prefix(struct inode *inode)
> >  }
> >  EXPORT_SYMBOL(xattr_supports_user_prefix);
> >  
> > +static int generic_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> > +			      struct vfs_caps *caps)
> > +{
> > +	struct inode *inode = d_inode(dentry);
> > +	struct vfs_ns_cap_data *nscaps = NULL;
> > +	int ret;
> > +
> > +	ret = (int)vfs_getxattr_alloc(idmap, dentry, XATTR_NAME_CAPS,
> 
> I don't think you need that case here.

Yep. I played with a few different implementations of this function, so
I'm guessing I did need it at one point and failed to notice when it was
no longer needed.

> 
> > +				      (char **)&nscaps, 0, GFP_NOFS);
> > +
> > +	if (ret >= 0)
> > +		ret = vfs_caps_from_xattr(idmap, i_user_ns(inode), caps, nscaps, ret);
> > +
> > +	kfree(nscaps);
> > +	return ret;
> > +}
> > +
> > +/**
> > + * __vfs_get_fscaps - get filesystem capabilities without security checks
> > + * @idmap: idmap of the mount the inode was found from
> > + * @dentry: the dentry from which to get filesystem capabilities
> > + * @caps: storage in which to return the filesystem capabilities
> > + *
> > + * This function gets the filesystem capabilities for the dentry and returns
> > + * them in @caps. It does not perform security checks.
> > + *
> > + * Return: 0 on success, a negative errno on error.
> > + */
> > +int __vfs_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> > +		     struct vfs_caps *caps)
> 
> I would rename that to vfs_get_fscaps_nosec(). We do that for
> vfs_getxattr_nosec() as well. It's not pretty but it's better than just
> slapping underscores onto it imo.

Will do.