linux-kernel - Re: [PATCH v2] xattr: Enable security.capability in user namespaces

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Date:   Tue, 11 Jul 2017 19:47:15 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        Stefan Berger <StefanBergerstefanb@...ux.vnet.ibm.com>,
        ebiederm@...ssion.com, containers@...ts.linux-foundation.org,
        lkp@...org, linux-kernel@...r.kernel.org, zohar@...ux.vnet.ibm.com,
        tycho@...ker.com, James.Bottomley@...senPartnership.com,
        vgoyal@...hat.com, christian.brauner@...lbox.org,
        amir73il@...il.com, linux-security-module@...r.kernel.org,
        casey@...aufler-ca.com
Subject: Re: [PATCH v2] xattr: Enable security.capability in user namespaces

Quoting Stefan Berger (stefanb@...ux.vnet.ibm.com):
> On 07/11/2017 01:12 PM, Serge E. Hallyn wrote:
> >>diff --git a/fs/xattr.c b/fs/xattr.c
> >>index 464c94b..eacad9e 100644
> >>--- a/fs/xattr.c
> >>+++ b/fs/xattr.c
> >>@@ -133,20 +133,440 @@ xattr_permission(struct inode *inode, const char *name, int mask)
> >>  	return inode_permission(inode, mask);
> >>  }
> >>+/*
> >>+ * A list of extended attributes that are supported in user namespaces
> >>+ */
> >>+static const char *const userns_xattrs[] = {
> >>+	XATTR_NAME_CAPS,
> >>+	NULL
> >>+};
> >>+
> >>+/*
> >>+ * xattrs_is_userns_supported - Check whether an xattr is supported in userns
> >>+ *
> >>+ * @name:   full name of the extended attribute
> >>+ * @prefix: do a prefix match (true) or a full match (false)
> >>+ *
> >>+ * This function returns < 0 if not supported, an index into userns_xattrs[]
> >>+ * otherwise.
> >>+ */
> >>+static int
> >>+xattr_is_userns_supported(const char *name, int prefix)
> >>+{
> >>+	int i;
> >>+
> >>+	if (!name)
> >>+		return -1;
> >>+
> >>+	for (i = 0; userns_xattrs[i]; i++) {
> >>+		if (prefix) {
> >>+			if (!strncmp(userns_xattrs[i], name,
> >>+				     strlen(userns_xattrs[i])))
> >>+				return i;
> >I think you here need to also check that the next char is either
> >'\0' or '.' (or maybe '@')
> 
> I have the checks for '@' and '\0' done by the caller. With the
> current support of only security.capability I don't think we need to
> check for '.'.

Ah - ok, thanks.