summaryrefslogtreecommitdiff
path: root/kernel/module/dups.c
blob: f3d7ea1e96d82b944839c3885de6d6027bad3334 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * kmod dups - the kernel module autoloader duplicate suppressor
 *
 * Copyright (C) 2023 Luis Chamberlain <mcgrof@kernel.org>
 */

#define pr_fmt(fmt)     "module: " fmt

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/binfmts.h>
#include <linux/syscalls.h>
#include <linux/unistd.h>
#include <linux/kmod.h>
#include <linux/slab.h>
#include <linux/completion.h>
#include <linux/cred.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/workqueue.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/resource.h>
#include <linux/notifier.h>
#include <linux/suspend.h>
#include <linux/rwsem.h>
#include <linux/ptrace.h>
#include <linux/async.h>
#include <linux/uaccess.h>

#include "internal.h"

#undef MODULE_PARAM_PREFIX
#define MODULE_PARAM_PREFIX "module."
static bool enable_dups_trace = IS_ENABLED(CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS_TRACE);
module_param(enable_dups_trace, bool_enable_only, 0644);

/*
 * Protects dup_kmod_reqs list, adds / removals with RCU.
 */
static DEFINE_MUTEX(kmod_dup_mutex);
static LIST_HEAD(dup_kmod_reqs);

struct kmod_dup_req {
	struct list_head list;
	char name[MODULE_NAME_LEN];
	struct completion first_req_done;
	struct work_struct complete_work;
	struct delayed_work delete_work;
	int dup_ret;
};

static struct kmod_dup_req *kmod_dup_request_lookup(char *module_name)
{
	struct kmod_dup_req *kmod_req;

	list_for_each_entry_rcu(kmod_req, &dup_kmod_reqs, list,
				lockdep_is_held(&kmod_dup_mutex)) {
		if (strlen(kmod_req->name) == strlen(module_name) &&
		    !memcmp(kmod_req->name, module_name, strlen(module_name))) {
			return kmod_req;
                }
        }

	return NULL;
}

static void kmod_dup_request_delete(struct work_struct *work)
{
	struct kmod_dup_req *kmod_req;
	kmod_req = container_of(to_delayed_work(work), struct kmod_dup_req, delete_work);

	/*
	 * The typical situation is a module successully loaded. In that
	 * situation the module will be present already in userspace. If
	 * new requests come in after that, userspace will already know the
	 * module is loaded so will just return 0 right away. There is still
	 * a small chance right after we delete this entry new request_module()
	 * calls may happen after that, they can happen. These heuristics
	 * are to protect finit_module() abuse for auto-loading, if modules
	 * are still tryign to auto-load even if a module is already loaded,
	 * that's on them, and those inneficiencies should not be fixed by
	 * kmod. The inneficies there are a call to modprobe and modprobe
	 * just returning 0.
	 */
	mutex_lock(&kmod_dup_mutex);
	list_del_rcu(&kmod_req->list);
	synchronize_rcu();
	mutex_unlock(&kmod_dup_mutex);
	kfree(kmod_req);
}

static void kmod_dup_request_complete(struct work_struct *work)
{
	struct kmod_dup_req *kmod_req;

	kmod_req = container_of(work, struct kmod_dup_req, complete_work);

	/*
	 * This will ensure that the kernel will let all the waiters get
	 * informed its time to check the return value. It's time to
	 * go home.
	 */
	complete_all(&kmod_req->first_req_done);

	/*
	 * Now that we have allowed prior request_module() calls to go on
	 * with life, let's schedule deleting this entry. We don't have
	 * to do it right away, but we *eventually* want to do it so to not
	 * let this linger forever as this is just a boot optimization for
	 * possible abuses of vmalloc() incurred by finit_module() thrashing.
	 */
	queue_delayed_work(system_wq, &kmod_req->delete_work, 60 * HZ);
}

bool kmod_dup_request_exists_wait(char *module_name, bool wait, int *dup_ret)
{
	struct kmod_dup_req *kmod_req, *new_kmod_req;
	int ret;

	/*
	 * Pre-allocate the entry in case we have to use it later
	 * to avoid contention with the mutex.
	 */
	new_kmod_req = kzalloc(sizeof(*new_kmod_req), GFP_KERNEL);
	if (!new_kmod_req)
		return false;

	memcpy(new_kmod_req->name, module_name, strlen(module_name));
	INIT_WORK(&new_kmod_req->complete_work, kmod_dup_request_complete);
	INIT_DELAYED_WORK(&new_kmod_req->delete_work, kmod_dup_request_delete);
	init_completion(&new_kmod_req->first_req_done);

	mutex_lock(&kmod_dup_mutex);

	kmod_req = kmod_dup_request_lookup(module_name);
	if (!kmod_req) {
		/*
		 * If the first request that came through for a module
		 * was with request_module_nowait() we cannot wait for it
		 * and share its return value with other users which may
		 * have used request_module() and need a proper return value
		 * so just skip using them as an anchor.
		 *
		 * If a prior request to this one came through with
		 * request_module() though, then a request_module_nowait()
		 * would benefit from duplicate detection.
		 */
		if (!wait) {
			kfree(new_kmod_req);
			pr_debug("New request_module_nowait() for %s -- cannot track duplicates for this request\n", module_name);
			mutex_unlock(&kmod_dup_mutex);
			return false;
		}

		/*
		 * There was no duplicate, just add the request so we can
		 * keep tab on duplicates later.
		 */
		pr_debug("New request_module() for %s\n", module_name);
		list_add_rcu(&new_kmod_req->list, &dup_kmod_reqs);
		mutex_unlock(&kmod_dup_mutex);
		return false;
	}
	mutex_unlock(&kmod_dup_mutex);

	/* We are dealing with a duplicate request now */
	kfree(new_kmod_req);

	/*
	 * To fix these try to use try_then_request_module() instead as that
	 * will check if the component you are looking for is present or not.
	 * You could also just queue a single request to load the module once,
	 * instead of having each and everything you need try to request for
	 * the module.
	 *
	 * Duplicate request_module() calls  can cause quite a bit of wasted
	 * vmalloc() space when racing with userspace.
	 */
	if (enable_dups_trace)
		WARN(1, "module-autoload: duplicate request for module %s\n", module_name);
	else
		pr_warn("module-autoload: duplicate request for module %s\n", module_name);

	if (!wait) {
		/*
		 * If request_module_nowait() was used then the user just
		 * wanted to issue the request and if another module request
		 * was already its way with the same name we don't care for
		 * the return value either. Let duplicate request_module_nowait()
		 * calls bail out right away.
		 */
		*dup_ret = 0;
		return true;
	}

	/*
	 * If a duplicate request_module() was used they *may* care for
	 * the return value, so we have no other option but to wait for
	 * the first caller to complete. If the first caller used
	 * the request_module_nowait() call, subsquent callers will
	 * deal with the comprmise of getting a successful call with this
	 * optimization enabled ...
	 */
	ret = wait_for_completion_state(&kmod_req->first_req_done,
					TASK_UNINTERRUPTIBLE | TASK_KILLABLE);
	if (ret) {
		*dup_ret = ret;
		return true;
	}

	/* Now the duplicate request has the same exact return value as the first request */
	*dup_ret = kmod_req->dup_ret;

	return true;
}

void kmod_dup_request_announce(char *module_name, int ret)
{
	struct kmod_dup_req *kmod_req;

	mutex_lock(&kmod_dup_mutex);

	kmod_req = kmod_dup_request_lookup(module_name);
	if (!kmod_req)
		goto out;

	kmod_req->dup_ret = ret;

	/*
	 * If we complete() here we may allow duplicate threads
	 * to continue before the first one that submitted the
	 * request. We're in no rush also, given that each and
	 * every bounce back to userspace is slow we avoid that
	 * with a slight delay here. So queueue up the completion
	 * and let duplicates suffer, just wait a tad bit longer.
	 * There is no rush. But we also don't want to hold the
	 * caller up forever or introduce any boot delays.
	 */
	queue_work(system_wq, &kmod_req->complete_work);

out:
	mutex_unlock(&kmod_dup_mutex);
}