Add `zfs allow` and `zfs unallow` support

ZFS allows for specific permissions to be delegated to normal users
with the `zfs allow` and `zfs unallow` commands.  In addition, non-
privileged users should be able to run all of the following commands:

  * zpool [list | iostat | status | get]
  * zfs [list | get]

Historically this functionality was not available on Linux.  In order
to add it the secpolicy_* functions needed to be implemented and mapped
to the equivalent Linux capability.  Only then could the permissions on
the `/dev/zfs` be relaxed and the internal ZFS permission checks used.

Even with this change some limitations remain.  Under Linux only the
root user is allowed to modify the namespace (unless it's a private
namespace).  This means the mount, mountpoint, canmount, unmount,
and remount delegations cannot be supported with the existing code.  It
may be possible to add this functionality in the future.

This functionality was validated with the cli_user and delegation test
cases from the ZFS Test Suite.  These tests exhaustively verify each
of the supported permissions which can be delegated and ensures only
an authorized user can perform it.

Two minor bug fixes were required for test-running.py.  First, the
Timer() object cannot be safely created in a `try:` block when there
is an unconditional `finally` block which references it.  Second,
when running as a normal user also check for scripts using the
both the .ksh and .sh suffixes.

Finally, existing users who are simulating delegations by setting
group permissions on the /dev/zfs device should revert that
customization when updating to a version with this change.

Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Tony Hutter <[email protected]>
Closes #362 
Closes #434 
Closes #4100
Closes #4394 
Closes #4410 
Closes #4487 

1 files changed, 303 insertions, 0 deletions

diff --git a/module/zfs/policy.c b/module/zfs/policy.c
new file mode 100644
index 000000000..81629e0dc
--- /dev/null
+++ b/module/zfs/policy.c
@@ -0,0 +1,303 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright 2013, Joyent, Inc. All rights reserved.
+ * Copyright (C) 2016 Lawrence Livermore National Security, LLC.
+ *
+ * For Linux the vast majority of this enforcement is already handled via
+ * the standard Linux VFS permission checks.  However certain administrative
+ * commands which bypass the standard mechanisms may need to make use of
+ * this functionality.
+ */
+
+#include <sys/policy.h>
+#include <linux/security.h>
+#include <linux/vfs_compat.h>
+
+/*
+ * The passed credentials cannot be directly verified because Linux only
+ * provides and interface to check the *current* proces credentials.  In
+ * order to handle this the capable() test is only run when the passed
+ * credentials match the current process credentials or the kcred.  In
+ * all other cases this function must fail and return the passed err.
+ */
+static int
+priv_policy(const cred_t *cr, int capability, boolean_t all, int err)
+{
+	ASSERT3S(all, ==, B_FALSE);
+
+	if (cr != CRED() && (cr != kcred))
+		return (err);
+
+	if (!capable(capability))
+		return (err);
+
+	return (0);
+}
+
+/*
+ * Checks for operations that are either client-only or are used by
+ * both clients and servers.
+ */
+int
+secpolicy_nfs(const cred_t *cr)
+{
+	return (priv_policy(cr, CAP_SYS_ADMIN, B_FALSE, EPERM));
+}
+
+/*
+ * Catch all system configuration.
+ */
+int
+secpolicy_sys_config(const cred_t *cr, boolean_t checkonly)
+{
+	return (priv_policy(cr, CAP_SYS_ADMIN, B_FALSE, EPERM));
+}
+
+/*
+ * Like secpolicy_vnode_access() but we get the actual wanted mode and the
+ * current mode of the file, not the missing bits.
+ *
+ * Enforced in the Linux VFS.
+ */
+int
+secpolicy_vnode_access2(const cred_t *cr, struct inode *ip, uid_t owner,
+	mode_t curmode, mode_t wantmode)
+{
+	return (0);
+}
+
+/*
+ * This is a special routine for ZFS; it is used to determine whether
+ * any of the privileges in effect allow any form of access to the
+ * file.  There's no reason to audit this or any reason to record
+ * this.  More work is needed to do the "KPLD" stuff.
+ */
+int
+secpolicy_vnode_any_access(const cred_t *cr, struct inode *ip, uid_t owner)
+{
+	if (crgetuid(cr) == owner)
+		return (0);
+
+	if (zpl_inode_owner_or_capable(ip))
+		return (0);
+
+	if (priv_policy(cr, CAP_DAC_OVERRIDE, B_FALSE, EPERM) == 0)
+		return (0);
+
+	if (priv_policy(cr, CAP_DAC_READ_SEARCH, B_FALSE, EPERM) == 0)
+		return (0);
+
+	return (EPERM);
+}
+
+/*
+ * Determine if subject can chown owner of a file.
+ */
+int
+secpolicy_vnode_chown(const cred_t *cr, uid_t owner)
+{
+	if (crgetuid(cr) == owner)
+		return (0);
+
+	return (priv_policy(cr, CAP_FOWNER, B_FALSE, EPERM));
+}
+
+/*
+ * Determine if subject can change group ownership of a file.
+ */
+int
+secpolicy_vnode_create_gid(const cred_t *cr)
+{
+	return (priv_policy(cr, CAP_SETGID, B_FALSE, EPERM));
+}
+
+/*
+ * Policy determines whether we can remove an entry from a directory,
+ * regardless of permission bits.
+ */
+int
+secpolicy_vnode_remove(const cred_t *cr)
+{
+	return (priv_policy(cr, CAP_FOWNER, B_FALSE, EPERM));
+}
+
+/*
+ * Determine that subject can modify the mode of a file.  allzone privilege
+ * needed when modifying root owned object.
+ */
+int
+secpolicy_vnode_setdac(const cred_t *cr, uid_t owner)
+{
+	if (crgetuid(cr) == owner)
+		return (0);
+
+	return (priv_policy(cr, CAP_FOWNER, B_FALSE, EPERM));
+}
+
+/*
+ * Are we allowed to retain the set-uid/set-gid bits when
+ * changing ownership or when writing to a file?
+ * "issuid" should be true when set-uid; only in that case
+ * root ownership is checked (setgid is assumed).
+ *
+ * Enforced in the Linux VFS.
+ */
+int
+secpolicy_vnode_setid_retain(const cred_t *cr, boolean_t issuidroot)
+{
+	return (0);
+}
+
+/*
+ * Determine that subject can set the file setgid flag.
+ */
+int
+secpolicy_vnode_setids_setgids(const cred_t *cr, gid_t gid)
+{
+	if (!groupmember(gid, cr))
+		return (priv_policy(cr, CAP_FSETID, B_FALSE, EPERM));
+
+	return (0);
+}
+
+/*
+ * Determine if the subject can inject faults in the ZFS fault injection
+ * framework.  Requires all privileges.
+ */
+int
+secpolicy_zinject(const cred_t *cr)
+{
+	return (priv_policy(cr, CAP_SYS_ADMIN, B_FALSE, EACCES));
+}
+
+/*
+ * Determine if the subject has permission to manipulate ZFS datasets
+ * (not pools).  Equivalent to the SYS_MOUNT privilege.
+ */
+int
+secpolicy_zfs(const cred_t *cr)
+{
+	return (priv_policy(cr, CAP_SYS_ADMIN, B_FALSE, EACCES));
+}
+
+void
+secpolicy_setid_clear(vattr_t *vap, cred_t *cr)
+{
+	if ((vap->va_mode & (S_ISUID | S_ISGID)) != 0 &&
+	    secpolicy_vnode_setid_retain(cr,
+	    (vap->va_mode & S_ISUID) != 0 &&
+	    (vap->va_mask & AT_UID) != 0 && vap->va_uid == 0) != 0) {
+		vap->va_mask |= AT_MODE;
+		vap->va_mode &= ~(S_ISUID|S_ISGID);
+	}
+}
+
+/*
+ * Determine that subject can set the file setid flags.
+ */
+static int
+secpolicy_vnode_setid_modify(const cred_t *cr, uid_t owner)
+{
+	if (crgetuid(cr) == owner)
+		return (0);
+
+	return (priv_policy(cr, CAP_FSETID, B_FALSE, EPERM));
+}
+
+/*
+ * Determine that subject can make a file a "sticky".
+ *
+ * Enforced in the Linux VFS.
+ */
+static int
+secpolicy_vnode_stky_modify(const cred_t *cr)
+{
+	return (0);
+}
+
+int
+secpolicy_setid_setsticky_clear(struct inode *ip, vattr_t *vap,
+    const vattr_t *ovap, cred_t *cr)
+{
+	int error;
+
+	if ((vap->va_mode & S_ISUID) != 0 &&
+	    (error = secpolicy_vnode_setid_modify(cr,
+	    ovap->va_uid)) != 0) {
+		return (error);
+	}
+
+	/*
+	 * Check privilege if attempting to set the
+	 * sticky bit on a non-directory.
+	 */
+	if (!S_ISDIR(ip->i_mode) && (vap->va_mode & S_ISVTX) != 0 &&
+	    secpolicy_vnode_stky_modify(cr) != 0) {
+		vap->va_mode &= ~S_ISVTX;
+	}
+
+	/*
+	 * Check for privilege if attempting to set the
+	 * group-id bit.
+	 */
+	if ((vap->va_mode & S_ISGID) != 0 &&
+	    secpolicy_vnode_setids_setgids(cr, ovap->va_gid) != 0) {
+		vap->va_mode &= ~S_ISGID;
+	}
+
+	return (0);
+}
+
+/*
+ * Check privileges for setting xvattr attributes
+ */
+int
+secpolicy_xvattr(xvattr_t *xvap, uid_t owner, cred_t *cr, vtype_t vtype)
+{
+	return (secpolicy_vnode_chown(cr, owner));
+}
+
+/*
+ * Check privileges for setattr attributes.
+ *
+ * Enforced in the Linux VFS.
+ */
+int
+secpolicy_vnode_setattr(cred_t *cr, struct inode *ip, struct vattr *vap,
+    const struct vattr *ovap, int flags,
+    int unlocked_access(void *, int, cred_t *), void *node)
+{
+	return (0);
+}
+
+/*
+ * Check privileges for links.
+ *
+ * Enforced in the Linux VFS.
+ */
+int
+secpolicy_basic_link(const cred_t *cr)
+{
+	return (0);
+}