GNU Linux-libre 4.19.211-gnu1
[releases.git] / security / loadpin / loadpin.c
1 /*
2  * Module and Firmware Pinning Security Module
3  *
4  * Copyright 2011-2016 Google Inc.
5  *
6  * Author: Kees Cook <keescook@chromium.org>
7  *
8  * This software is licensed under the terms of the GNU General Public
9  * License version 2, as published by the Free Software Foundation, and
10  * may be copied, distributed, and modified under those terms.
11  *
12  * This program is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15  * GNU General Public License for more details.
16  */
17
18 #define pr_fmt(fmt) "LoadPin: " fmt
19
20 #include <linux/module.h>
21 #include <linux/fs.h>
22 #include <linux/lsm_hooks.h>
23 #include <linux/mount.h>
24 #include <linux/path.h>
25 #include <linux/sched.h>        /* current */
26 #include <linux/string_helpers.h>
27
28 static void report_load(const char *origin, struct file *file, char *operation)
29 {
30         char *cmdline, *pathname;
31
32         pathname = kstrdup_quotable_file(file, GFP_KERNEL);
33         cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
34
35         pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
36                   origin, operation,
37                   (pathname && pathname[0] != '<') ? "\"" : "",
38                   pathname,
39                   (pathname && pathname[0] != '<') ? "\"" : "",
40                   task_pid_nr(current),
41                   cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
42
43         kfree(cmdline);
44         kfree(pathname);
45 }
46
47 static int enabled = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENABLED);
48 static struct super_block *pinned_root;
49 static DEFINE_SPINLOCK(pinned_root_spinlock);
50
51 #ifdef CONFIG_SYSCTL
52 static int zero;
53 static int one = 1;
54
55 static struct ctl_path loadpin_sysctl_path[] = {
56         { .procname = "kernel", },
57         { .procname = "loadpin", },
58         { }
59 };
60
61 static struct ctl_table loadpin_sysctl_table[] = {
62         {
63                 .procname       = "enabled",
64                 .data           = &enabled,
65                 .maxlen         = sizeof(int),
66                 .mode           = 0644,
67                 .proc_handler   = proc_dointvec_minmax,
68                 .extra1         = &zero,
69                 .extra2         = &one,
70         },
71         { }
72 };
73
74 /*
75  * This must be called after early kernel init, since then the rootdev
76  * is available.
77  */
78 static void check_pinning_enforcement(struct super_block *mnt_sb)
79 {
80         bool ro = false;
81
82         /*
83          * If load pinning is not enforced via a read-only block
84          * device, allow sysctl to change modes for testing.
85          */
86         if (mnt_sb->s_bdev) {
87                 ro = bdev_read_only(mnt_sb->s_bdev);
88                 pr_info("dev(%u,%u): %s\n",
89                         MAJOR(mnt_sb->s_bdev->bd_dev),
90                         MINOR(mnt_sb->s_bdev->bd_dev),
91                         ro ? "read-only" : "writable");
92         } else
93                 pr_info("mnt_sb lacks block device, treating as: writable\n");
94
95         if (!ro) {
96                 if (!register_sysctl_paths(loadpin_sysctl_path,
97                                            loadpin_sysctl_table))
98                         pr_notice("sysctl registration failed!\n");
99                 else
100                         pr_info("load pinning can be disabled.\n");
101         } else
102                 pr_info("load pinning engaged.\n");
103 }
104 #else
105 static void check_pinning_enforcement(struct super_block *mnt_sb)
106 {
107         pr_info("load pinning engaged.\n");
108 }
109 #endif
110
111 static void loadpin_sb_free_security(struct super_block *mnt_sb)
112 {
113         /*
114          * When unmounting the filesystem we were using for load
115          * pinning, we acknowledge the superblock release, but make sure
116          * no other modules or firmware can be loaded.
117          */
118         if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
119                 pinned_root = ERR_PTR(-EIO);
120                 pr_info("umount pinned fs: refusing further loads\n");
121         }
122 }
123
124 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
125 {
126         struct super_block *load_root;
127         const char *origin = kernel_read_file_id_str(id);
128
129         /* This handles the older init_module API that has a NULL file. */
130         if (!file) {
131                 if (!enabled) {
132                         report_load(origin, NULL, "old-api-pinning-ignored");
133                         return 0;
134                 }
135
136                 report_load(origin, NULL, "old-api-denied");
137                 return -EPERM;
138         }
139
140         load_root = file->f_path.mnt->mnt_sb;
141
142         /* First loaded module/firmware defines the root for all others. */
143         spin_lock(&pinned_root_spinlock);
144         /*
145          * pinned_root is only NULL at startup. Otherwise, it is either
146          * a valid reference, or an ERR_PTR.
147          */
148         if (!pinned_root) {
149                 pinned_root = load_root;
150                 /*
151                  * Unlock now since it's only pinned_root we care about.
152                  * In the worst case, we will (correctly) report pinning
153                  * failures before we have announced that pinning is
154                  * enabled. This would be purely cosmetic.
155                  */
156                 spin_unlock(&pinned_root_spinlock);
157                 check_pinning_enforcement(pinned_root);
158                 report_load(origin, file, "pinned");
159         } else {
160                 spin_unlock(&pinned_root_spinlock);
161         }
162
163         if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
164                 if (unlikely(!enabled)) {
165                         report_load(origin, file, "pinning-ignored");
166                         return 0;
167                 }
168
169                 report_load(origin, file, "denied");
170                 return -EPERM;
171         }
172
173         return 0;
174 }
175
176 static int loadpin_load_data(enum kernel_load_data_id id)
177 {
178         return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
179 }
180
181 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
182         LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
183         LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
184         LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
185 };
186
187 void __init loadpin_add_hooks(void)
188 {
189         pr_info("ready to pin (currently %sabled)", enabled ? "en" : "dis");
190         security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
191 }
192
193 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
194 module_param(enabled, int, 0);
195 MODULE_PARM_DESC(enabled, "Pin module/firmware loading (default: true)");