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Message-ID: <be91c7158b1b9bed35aa9c3205e8f8e467778a5f.camel@huaweicloud.com>
Subject: Re: [PATCH v2 06/25] capability: provide helpers for converting
 between xattrs and vfs_caps
From: Roberto Sassu <roberto.sassu@huaweicloud.com>
To: "Seth Forshee (DigitalOcean)" <sforshee@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>, Serge Hallyn <serge@hallyn.com>,
  Paul Moore <paul@paul-moore.com>, Eric Paris <eparis@redhat.com>, James
 Morris <jmorris@namei.org>,  Alexander Viro <viro@zeniv.linux.org.uk>, Jan
 Kara <jack@suse.cz>, Stephen Smalley <stephen.smalley.work@gmail.com>,
 Ondrej Mosnacek <omosnace@redhat.com>,  Casey Schaufler
 <casey@schaufler-ca.com>, Mimi Zohar <zohar@linux.ibm.com>, Roberto Sassu
 <roberto.sassu@huawei.com>,  Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
 Eric Snowberg <eric.snowberg@oracle.com>, "Matthew Wilcox (Oracle)"
 <willy@infradead.org>, Jonathan Corbet <corbet@lwn.net>, Miklos Szeredi
 <miklos@szeredi.hu>, Amir Goldstein <amir73il@gmail.com>, 
 linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, 
 linux-security-module@vger.kernel.org, audit@vger.kernel.org, 
 selinux@vger.kernel.org, linux-integrity@vger.kernel.org, 
 linux-doc@vger.kernel.org, linux-unionfs@vger.kernel.org
Date: Mon, 04 Mar 2024 09:33:06 +0100
In-Reply-To: <ZeIlwkUx5lNBrdS9@do-x1extreme>
References: <20240221-idmap-fscap-refactor-v2-0-3039364623bd@kernel.org>
	 <20240221-idmap-fscap-refactor-v2-6-3039364623bd@kernel.org>
	 <7633ab5d5359116a602cdc8f85afd2561047960e.camel@huaweicloud.com>
	 <ZeIlwkUx5lNBrdS9@do-x1extreme>
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On Fri, 2024-03-01 at 13:00 -0600, Seth Forshee (DigitalOcean) wrote:
> On Fri, Mar 01, 2024 at 05:30:55PM +0100, Roberto Sassu wrote:
> > > +/*
> > > + * Inner implementation of vfs_caps_to_xattr() which does not return=
 an
> > > + * error if the rootid does not map into @dest_userns.
> > > + */
> > > +static ssize_t __vfs_caps_to_xattr(struct mnt_idmap *idmap,
> > > +				   struct user_namespace *dest_userns,
> > > +				   const struct vfs_caps *vfs_caps,
> > > +				   void *data, size_t size)
> > > +{
> > > +	struct vfs_ns_cap_data *ns_caps =3D data;
> > > +	struct vfs_cap_data *caps =3D (struct vfs_cap_data *)ns_caps;
> > > +	kuid_t rootkuid;
> > > +	uid_t rootid;
> > > +
> > > +	memset(ns_caps, 0, size);
> >=20
> > size -> sizeof(*ns_caps) (or an equivalent change)
>=20
> This is zeroing out the passed buffer, so it should use the size passed
> for the buffer. sizeof(*ns_caps) could potentially be more than the size
> of the buffer.

Uhm, then maybe the problem is that you are passing the wrong argument?

ssize_t
do_getxattr(struct mnt_idmap *idmap, struct dentry *d,
	struct xattr_ctx *ctx)
{
	ssize_t error;
	char *kname =3D ctx->kname->name;

	if (is_fscaps_xattr(kname)) {
		struct vfs_caps caps;
		struct vfs_ns_cap_data data;
		int ret;

		ret =3D vfs_get_fscaps(idmap, d, &caps);
		if (ret)
			return ret;
		/*
		 * rootid is already in the mount idmap, so pass nop_mnt_idmap
		 * so that it won't be mapped.
		 */
		ret =3D vfs_caps_to_user_xattr(&nop_mnt_idmap, current_user_ns(),
					     &caps, &data, ctx->size);


ctx->size in my case is 1024 bytes.

Roberto

> Maybe it would be clearer if it was memset(data, 0, size)?
>=20
> > I was zeroing more (the size of the buffer passed to vfs_getxattr()).
> >=20
> > Roberto