Merge tag 'devicetree-fixes-for-5.15-3' of git://git.kernel.org/pub/scm/linux/kernel...
[muen/linux.git] / security / loadpin / loadpin.c
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Module and Firmware Pinning Security Module
4  *
5  * Copyright 2011-2016 Google Inc.
6  *
7  * Author: Kees Cook <keescook@chromium.org>
8  */
9
10 #define pr_fmt(fmt) "LoadPin: " fmt
11
12 #include <linux/module.h>
13 #include <linux/fs.h>
14 #include <linux/kernel_read_file.h>
15 #include <linux/lsm_hooks.h>
16 #include <linux/mount.h>
17 #include <linux/blkdev.h>
18 #include <linux/path.h>
19 #include <linux/sched.h>        /* current */
20 #include <linux/string_helpers.h>
21
22 static void report_load(const char *origin, struct file *file, char *operation)
23 {
24         char *cmdline, *pathname;
25
26         pathname = kstrdup_quotable_file(file, GFP_KERNEL);
27         cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
28
29         pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
30                   origin, operation,
31                   (pathname && pathname[0] != '<') ? "\"" : "",
32                   pathname,
33                   (pathname && pathname[0] != '<') ? "\"" : "",
34                   task_pid_nr(current),
35                   cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
36
37         kfree(cmdline);
38         kfree(pathname);
39 }
40
41 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
42 static char *exclude_read_files[READING_MAX_ID];
43 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
44 static struct super_block *pinned_root;
45 static DEFINE_SPINLOCK(pinned_root_spinlock);
46
47 #ifdef CONFIG_SYSCTL
48
49 static struct ctl_path loadpin_sysctl_path[] = {
50         { .procname = "kernel", },
51         { .procname = "loadpin", },
52         { }
53 };
54
55 static struct ctl_table loadpin_sysctl_table[] = {
56         {
57                 .procname       = "enforce",
58                 .data           = &enforce,
59                 .maxlen         = sizeof(int),
60                 .mode           = 0644,
61                 .proc_handler   = proc_dointvec_minmax,
62                 .extra1         = SYSCTL_ZERO,
63                 .extra2         = SYSCTL_ONE,
64         },
65         { }
66 };
67
68 /*
69  * This must be called after early kernel init, since then the rootdev
70  * is available.
71  */
72 static void check_pinning_enforcement(struct super_block *mnt_sb)
73 {
74         bool ro = false;
75
76         /*
77          * If load pinning is not enforced via a read-only block
78          * device, allow sysctl to change modes for testing.
79          */
80         if (mnt_sb->s_bdev) {
81                 char bdev[BDEVNAME_SIZE];
82
83                 ro = bdev_read_only(mnt_sb->s_bdev);
84                 bdevname(mnt_sb->s_bdev, bdev);
85                 pr_info("%s (%u:%u): %s\n", bdev,
86                         MAJOR(mnt_sb->s_bdev->bd_dev),
87                         MINOR(mnt_sb->s_bdev->bd_dev),
88                         ro ? "read-only" : "writable");
89         } else
90                 pr_info("mnt_sb lacks block device, treating as: writable\n");
91
92         if (!ro) {
93                 if (!register_sysctl_paths(loadpin_sysctl_path,
94                                            loadpin_sysctl_table))
95                         pr_notice("sysctl registration failed!\n");
96                 else
97                         pr_info("enforcement can be disabled.\n");
98         } else
99                 pr_info("load pinning engaged.\n");
100 }
101 #else
102 static void check_pinning_enforcement(struct super_block *mnt_sb)
103 {
104         pr_info("load pinning engaged.\n");
105 }
106 #endif
107
108 static void loadpin_sb_free_security(struct super_block *mnt_sb)
109 {
110         /*
111          * When unmounting the filesystem we were using for load
112          * pinning, we acknowledge the superblock release, but make sure
113          * no other modules or firmware can be loaded.
114          */
115         if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
116                 pinned_root = ERR_PTR(-EIO);
117                 pr_info("umount pinned fs: refusing further loads\n");
118         }
119 }
120
121 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
122                              bool contents)
123 {
124         struct super_block *load_root;
125         const char *origin = kernel_read_file_id_str(id);
126
127         /*
128          * If we will not know that we'll be seeing the full contents
129          * then we cannot trust a load will be complete and unchanged
130          * off disk. Treat all contents=false hooks as if there were
131          * no associated file struct.
132          */
133         if (!contents)
134                 file = NULL;
135
136         /* If the file id is excluded, ignore the pinning. */
137         if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
138             ignore_read_file_id[id]) {
139                 report_load(origin, file, "pinning-excluded");
140                 return 0;
141         }
142
143         /* This handles the older init_module API that has a NULL file. */
144         if (!file) {
145                 if (!enforce) {
146                         report_load(origin, NULL, "old-api-pinning-ignored");
147                         return 0;
148                 }
149
150                 report_load(origin, NULL, "old-api-denied");
151                 return -EPERM;
152         }
153
154         load_root = file->f_path.mnt->mnt_sb;
155
156         /* First loaded module/firmware defines the root for all others. */
157         spin_lock(&pinned_root_spinlock);
158         /*
159          * pinned_root is only NULL at startup. Otherwise, it is either
160          * a valid reference, or an ERR_PTR.
161          */
162         if (!pinned_root) {
163                 pinned_root = load_root;
164                 /*
165                  * Unlock now since it's only pinned_root we care about.
166                  * In the worst case, we will (correctly) report pinning
167                  * failures before we have announced that pinning is
168                  * enforcing. This would be purely cosmetic.
169                  */
170                 spin_unlock(&pinned_root_spinlock);
171                 check_pinning_enforcement(pinned_root);
172                 report_load(origin, file, "pinned");
173         } else {
174                 spin_unlock(&pinned_root_spinlock);
175         }
176
177         if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
178                 if (unlikely(!enforce)) {
179                         report_load(origin, file, "pinning-ignored");
180                         return 0;
181                 }
182
183                 report_load(origin, file, "denied");
184                 return -EPERM;
185         }
186
187         return 0;
188 }
189
190 static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
191 {
192         return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents);
193 }
194
195 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
196         LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
197         LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
198         LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
199 };
200
201 static void __init parse_exclude(void)
202 {
203         int i, j;
204         char *cur;
205
206         /*
207          * Make sure all the arrays stay within expected sizes. This
208          * is slightly weird because kernel_read_file_str[] includes
209          * READING_MAX_ID, which isn't actually meaningful here.
210          */
211         BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
212                      ARRAY_SIZE(ignore_read_file_id));
213         BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
214                      ARRAY_SIZE(ignore_read_file_id));
215
216         for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
217                 cur = exclude_read_files[i];
218                 if (!cur)
219                         break;
220                 if (*cur == '\0')
221                         continue;
222
223                 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
224                         if (strcmp(cur, kernel_read_file_str[j]) == 0) {
225                                 pr_info("excluding: %s\n",
226                                         kernel_read_file_str[j]);
227                                 ignore_read_file_id[j] = 1;
228                                 /*
229                                  * Can not break, because one read_file_str
230                                  * may map to more than on read_file_id.
231                                  */
232                         }
233                 }
234         }
235 }
236
237 static int __init loadpin_init(void)
238 {
239         pr_info("ready to pin (currently %senforcing)\n",
240                 enforce ? "" : "not ");
241         parse_exclude();
242         security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
243         return 0;
244 }
245
246 DEFINE_LSM(loadpin) = {
247         .name = "loadpin",
248         .init = loadpin_init,
249 };
250
251 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
252 module_param(enforce, int, 0);
253 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
254 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
255 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");