1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22/*
23 * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
24 * Use is subject to license terms.
25 */
26
27/*	Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T	*/
28/*	  All Rights Reserved  	*/
29
30/*
31 * Portions of this source code were derived from Berkeley 4.3 BSD
32 * under license from the Regents of the University of California.
33 */
34
35#include <sys/types.h>
36#include <sys/t_lock.h>
37#include <sys/param.h>
38#include <sys/errno.h>
39#include <sys/fstyp.h>
40#include <sys/kmem.h>
41#include <sys/systm.h>
42#include <sys/mount.h>
43#include <sys/vfs.h>
44#include <sys/cred.h>
45#include <sys/vnode.h>
46#include <sys/cmn_err.h>
47#include <sys/debug.h>
48#include <sys/pathname.h>
49#include <sys/policy.h>
50#include <sys/zone.h>
51
52#define	UMOUNT2_SET_ERRNO(e, is_syscall) ((is_syscall) ? set_errno((e)) : (e))
53
54/*
55 * The heart of the umount2 call - it is pulled out to allow kernel
56 * level particpation when the only reference is the vfs pointer.
57 *
58 * Note that some of the callers may not be in the context of a
59 * syscall (created by zthread_create() for example) and as such
60 * may not have an associated curthread->t_lwp. This is handled
61 * by is_syscall.
62 */
63int
64umount2_engine(vfs_t *vfsp, int flag, cred_t *cr, int is_syscall)
65{
66	int	error;
67
68	/*
69	 * Protect the call to vn_vfswlock() with the vfs reflock.  This
70	 * ensures vfs_vnodecovered will either be NULL (because someone
71	 * beat us to the umount) or valid (because vfs_lock() prevents
72	 * another umount from getting through here until we've called
73	 * vn_vfswlock() on the covered vnode).
74	 *
75	 * At one point, we did the non-blocking version (vfs_lock()),
76	 * and if it failed, bailed out with EBUSY.  However, dounmount()
77	 * calls vfs_lock_wait() and we drop the vfs lock before calling
78	 * dounmount(), so there's no difference between waiting here
79	 * for the lock or waiting there because grabbed it as soon as
80	 * we drop it below.  No returning with EBUSY at this point
81	 * reduces the number of spurious unmount failures that happen
82	 * as a side-effect of fsflush() and other mount and unmount
83	 * operations that might be going on simultaneously.
84	 */
85	vfs_lock_wait(vfsp);
86
87	/*
88	 * Call vn_vfswlock() on the covered vnode so that dounmount()
89	 * can do its thing.  It will call the corresponding vn_vfsunlock().
90	 * Note that vfsp->vfs_vnodecovered can be NULL here, either because
91	 * someone did umount on "/" or because someone beat us to the umount
92	 * before we did the vfs_lock() above.  In these cases, vn_vfswlock()
93	 * returns EBUSY and we just pass that up.  Also note that we're
94	 * looking at a vnode without doing a VN_HOLD() on it.  This is
95	 * safe because it can't go away while something is mounted on it
96	 * and we're locking out other umounts at this point.
97	 */
98	if (vn_vfswlock(vfsp->vfs_vnodecovered)) {
99		vfs_unlock(vfsp);
100		VFS_RELE(vfsp);
101		return (UMOUNT2_SET_ERRNO(EBUSY, is_syscall));
102	}
103
104	/*
105	 * Now that the VVFSLOCK in the covered vnode is protecting this
106	 * path, we don't need the vfs reflock or the hold on the vfs anymore.
107	 */
108	vfs_unlock(vfsp);
109	VFS_RELE(vfsp);
110
111	/*
112	 * Perform the unmount.
113	 */
114	if ((error = dounmount(vfsp, flag, cr)) != 0)
115		return (UMOUNT2_SET_ERRNO(error, is_syscall));
116	return (0);
117}
118
119/*
120 * New umount() system call (for force unmount flag and perhaps others later).
121 */
122int
123umount2(char *pathp, int flag)
124{
125	struct pathname pn;
126	struct vfs *vfsp;
127	int error;
128
129	/*
130	 * Some flags are disallowed through the system call interface.
131	 */
132	flag &= MS_UMOUNT_MASK;
133
134	/*
135	 * Lookup user-supplied name by trying to match it against the
136	 * mount points recorded at mount time.  If no match is found
137	 * (which can happen if the path to the mount point is specified
138	 * differently between mount & umount, or if a block device were
139	 * passed to umount) then we fall back to calling lookupname()
140	 * to find the vfs.  Doing it this way prevents calling lookupname()
141	 * in most cases and that allows forcible umount to work even if
142	 * lookupname() would hang (i.e. because an NFS server is dead).
143	 */
144
145	if (error = pn_get(pathp, UIO_USERSPACE, &pn))
146		return (set_errno(error));
147
148	/*
149	 * Only a privileged user is allowed to bypass the security
150	 * checks done by lookupname() and use the results from
151	 * vfs_mntpoint2vfsp() instead.  It could be argued that the
152	 * proper check is FILE_DAC_SEARCH but we put it all
153	 * under the mount privilege.  Also, make sure the caller
154	 * isn't in an environment with an alternate root (to the zone's root)
155	 * directory, i.e. chroot(2).
156	 */
157	if (secpolicy_fs_unmount(CRED(), NULL) != 0 ||
158	    (PTOU(curproc)->u_rdir != NULL &&
159	    PTOU(curproc)->u_rdir != curproc->p_zone->zone_rootvp) ||
160	    (vfsp = vfs_mntpoint2vfsp(pn.pn_path)) == NULL) {
161		vnode_t *fsrootvp;
162
163		/* fall back to lookupname() on path given to us */
164		if (error = lookupname(pn.pn_path, UIO_SYSSPACE, FOLLOW,
165		    NULLVPP, &fsrootvp)) {
166			pn_free(&pn);
167			return (set_errno(error));
168		}
169		/*
170		 * Find the vfs to be unmounted.  The caller may have specified
171		 * either the directory mount point (preferred) or else (for a
172		 * disk-based file system) the block device which was mounted.
173		 * Check to see which it is; if it's the device, search the VFS
174		 * list to find the associated vfs entry.
175		 */
176		if (fsrootvp->v_flag & VROOT) {
177			vfsp = fsrootvp->v_vfsp;
178			VFS_HOLD(vfsp);
179		} else if (fsrootvp->v_type == VBLK)
180			vfsp = vfs_dev2vfsp(fsrootvp->v_rdev);
181		else
182			vfsp = NULL;
183
184		VN_RELE(fsrootvp);
185
186		if (vfsp == NULL) {
187			pn_free(&pn);
188			return (set_errno(EINVAL));
189		}
190	}
191	pn_free(&pn);
192
193	return (umount2_engine(vfsp, flag, CRED(), 1));
194}
195