Root/security/apparmor/path.c

1/*
2 * AppArmor security module
3 *
4 * This file contains AppArmor function for pathnames
5 *
6 * Copyright (C) 1998-2008 Novell/SUSE
7 * Copyright 2009-2010 Canonical Ltd.
8 *
9 * This program is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU General Public License as
11 * published by the Free Software Foundation, version 2 of the
12 * License.
13 */
14
15#include <linux/magic.h>
16#include <linux/mnt_namespace.h>
17#include <linux/mount.h>
18#include <linux/namei.h>
19#include <linux/nsproxy.h>
20#include <linux/path.h>
21#include <linux/sched.h>
22#include <linux/slab.h>
23#include <linux/fs_struct.h>
24
25#include "include/apparmor.h"
26#include "include/path.h"
27#include "include/policy.h"
28
29
30/* modified from dcache.c */
31static int prepend(char **buffer, int buflen, const char *str, int namelen)
32{
33    buflen -= namelen;
34    if (buflen < 0)
35        return -ENAMETOOLONG;
36    *buffer -= namelen;
37    memcpy(*buffer, str, namelen);
38    return 0;
39}
40
41#define CHROOT_NSCONNECT (PATH_CHROOT_REL | PATH_CHROOT_NSCONNECT)
42
43/**
44 * d_namespace_path - lookup a name associated with a given path
45 * @path: path to lookup (NOT NULL)
46 * @buf: buffer to store path to (NOT NULL)
47 * @buflen: length of @buf
48 * @name: Returns - pointer for start of path name with in @buf (NOT NULL)
49 * @flags: flags controlling path lookup
50 *
51 * Handle path name lookup.
52 *
53 * Returns: %0 else error code if path lookup fails
54 * When no error the path name is returned in @name which points to
55 * to a position in @buf
56 */
57static int d_namespace_path(struct path *path, char *buf, int buflen,
58                char **name, int flags)
59{
60    struct path root, tmp;
61    char *res;
62    int connected, error = 0;
63
64    /* Get the root we want to resolve too, released below */
65    if (flags & PATH_CHROOT_REL) {
66        /* resolve paths relative to chroot */
67        get_fs_root(current->fs, &root);
68    } else {
69        /* resolve paths relative to namespace */
70        root.mnt = current->nsproxy->mnt_ns->root;
71        root.dentry = root.mnt->mnt_root;
72        path_get(&root);
73    }
74
75    spin_lock(&dcache_lock);
76    tmp = root;
77    res = __d_path(path, &tmp, buf, buflen);
78    spin_unlock(&dcache_lock);
79
80    *name = res;
81    /* handle error conditions - and still allow a partial path to
82     * be returned.
83     */
84    if (IS_ERR(res)) {
85        error = PTR_ERR(res);
86        *name = buf;
87        goto out;
88    }
89
90    /* Handle two cases:
91     * 1. A deleted dentry && profile is not allowing mediation of deleted
92     * 2. On some filesystems, newly allocated dentries appear to the
93     * security_path hooks as a deleted dentry except without an inode
94     * allocated.
95     */
96    if (d_unlinked(path->dentry) && path->dentry->d_inode &&
97        !(flags & PATH_MEDIATE_DELETED)) {
98            error = -ENOENT;
99            goto out;
100    }
101
102    /* Determine if the path is connected to the expected root */
103    connected = tmp.dentry == root.dentry && tmp.mnt == root.mnt;
104
105    /* If the path is not connected,
106     * check if it is a sysctl and handle specially else remove any
107     * leading / that __d_path may have returned.
108     * Unless
109     * specifically directed to connect the path,
110     * OR
111     * if in a chroot and doing chroot relative paths and the path
112     * resolves to the namespace root (would be connected outside
113     * of chroot) and specifically directed to connect paths to
114     * namespace root.
115     */
116    if (!connected) {
117        /* is the disconnect path a sysctl? */
118        if (tmp.dentry->d_sb->s_magic == PROC_SUPER_MAGIC &&
119            strncmp(*name, "/sys/", 5) == 0) {
120            /* TODO: convert over to using a per namespace
121             * control instead of hard coded /proc
122             */
123            error = prepend(name, *name - buf, "/proc", 5);
124        } else if (!(flags & PATH_CONNECT_PATH) &&
125               !(((flags & CHROOT_NSCONNECT) == CHROOT_NSCONNECT) &&
126                 (tmp.mnt == current->nsproxy->mnt_ns->root &&
127                  tmp.dentry == tmp.mnt->mnt_root))) {
128            /* disconnected path, don't return pathname starting
129             * with '/'
130             */
131            error = -ESTALE;
132            if (*res == '/')
133                *name = res + 1;
134        }
135    }
136
137out:
138    path_put(&root);
139
140    return error;
141}
142
143/**
144 * get_name_to_buffer - get the pathname to a buffer ensure dir / is appended
145 * @path: path to get name for (NOT NULL)
146 * @flags: flags controlling path lookup
147 * @buffer: buffer to put name in (NOT NULL)
148 * @size: size of buffer
149 * @name: Returns - contains position of path name in @buffer (NOT NULL)
150 *
151 * Returns: %0 else error on failure
152 */
153static int get_name_to_buffer(struct path *path, int flags, char *buffer,
154                  int size, char **name)
155{
156    int adjust = (flags & PATH_IS_DIR) ? 1 : 0;
157    int error = d_namespace_path(path, buffer, size - adjust, name, flags);
158
159    if (!error && (flags & PATH_IS_DIR) && (*name)[1] != '\0')
160        /*
161         * Append "/" to the pathname. The root directory is a special
162         * case; it already ends in slash.
163         */
164        strcpy(&buffer[size - 2], "/");
165
166    return error;
167}
168
169/**
170 * aa_get_name - compute the pathname of a file
171 * @path: path the file (NOT NULL)
172 * @flags: flags controlling path name generation
173 * @buffer: buffer that aa_get_name() allocated (NOT NULL)
174 * @name: Returns - the generated path name if !error (NOT NULL)
175 *
176 * @name is a pointer to the beginning of the pathname (which usually differs
177 * from the beginning of the buffer), or NULL. If there is an error @name
178 * may contain a partial or invalid name that can be used for audit purposes,
179 * but it can not be used for mediation.
180 *
181 * We need PATH_IS_DIR to indicate whether the file is a directory or not
182 * because the file may not yet exist, and so we cannot check the inode's
183 * file type.
184 *
185 * Returns: %0 else error code if could retrieve name
186 */
187int aa_get_name(struct path *path, int flags, char **buffer, const char **name)
188{
189    char *buf, *str = NULL;
190    int size = 256;
191    int error;
192
193    *name = NULL;
194    *buffer = NULL;
195    for (;;) {
196        /* freed by caller */
197        buf = kmalloc(size, GFP_KERNEL);
198        if (!buf)
199            return -ENOMEM;
200
201        error = get_name_to_buffer(path, flags, buf, size, &str);
202        if (error != -ENAMETOOLONG)
203            break;
204
205        kfree(buf);
206        size <<= 1;
207        if (size > aa_g_path_max)
208            return -ENAMETOOLONG;
209    }
210    *buffer = buf;
211    *name = str;
212
213    return error;
214}
215

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