linux-kernel - Re: [PATCH v2 06/25] capability: provide helpers for converting between xattrs and vfs

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Message-ID: <ZeIlwkUx5lNBrdS9@do-x1extreme>
Date: Fri, 1 Mar 2024 13:00:18 -0600
From: "Seth Forshee (DigitalOcean)" <sforshee@...nel.org>
To: Roberto Sassu <roberto.sassu@...weicloud.com>
Cc: Christian Brauner <brauner@...nel.org>, Serge Hallyn <serge@...lyn.com>,
	Paul Moore <paul@...l-moore.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 06/25] capability: provide helpers for converting
 between xattrs and vfs_caps

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 = data;
> > +	struct vfs_cap_data *caps = (struct vfs_cap_data *)ns_caps;
> > +	kuid_t rootkuid;
> > +	uid_t rootid;
> > +
> > +	memset(ns_caps, 0, size);
> 
> size -> sizeof(*ns_caps) (or an equivalent change)

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.

Maybe it would be clearer if it was memset(data, 0, size)?

> I was zeroing more (the size of the buffer passed to vfs_getxattr()).
> 
> Roberto