1/* SPDX-License-Identifier: GPL-2.0-or-later */
  2/*
  3 * kmod dups - the kernel module autoloader duplicate suppressor
  4 *
  5 * Copyright (C) 2023 Luis Chamberlain <mcgrof@kernel.org>
  6 */
  7
  8#define pr_fmt(fmt)     "module: " fmt
  9
 10#include <linux/module.h>
 11#include <linux/sched.h>
 12#include <linux/sched/task.h>
 13#include <linux/binfmts.h>
 14#include <linux/syscalls.h>
 15#include <linux/unistd.h>
 16#include <linux/kmod.h>
 17#include <linux/slab.h>
 18#include <linux/completion.h>
 19#include <linux/cred.h>
 20#include <linux/file.h>
 21#include <linux/workqueue.h>
 22#include <linux/security.h>
 23#include <linux/mount.h>
 24#include <linux/kernel.h>
 25#include <linux/init.h>
 26#include <linux/resource.h>
 27#include <linux/notifier.h>
 28#include <linux/suspend.h>
 29#include <linux/rwsem.h>
 30#include <linux/ptrace.h>
 31#include <linux/async.h>
 32#include <linux/uaccess.h>
 33
 34#include "internal.h"
 35
 36#undef MODULE_PARAM_PREFIX
 37#define MODULE_PARAM_PREFIX "module."
 38static bool enable_dups_trace = IS_ENABLED(CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS_TRACE);
 39module_param(enable_dups_trace, bool_enable_only, 0644);
 40
 41/*
 42 * Protects dup_kmod_reqs list, adds / removals with RCU.
 43 */
 44static DEFINE_MUTEX(kmod_dup_mutex);
 45static LIST_HEAD(dup_kmod_reqs);
 46
 47struct kmod_dup_req {
 48	struct list_head list;
 49	char name[MODULE_NAME_LEN];
 50	struct completion first_req_done;
 51	struct work_struct complete_work;
 52	struct delayed_work delete_work;
 53	int dup_ret;
 54};
 55
 56static struct kmod_dup_req *kmod_dup_request_lookup(char *module_name)
 57{
 58	struct kmod_dup_req *kmod_req;
 59
 60	list_for_each_entry_rcu(kmod_req, &dup_kmod_reqs, list,
 61				lockdep_is_held(&kmod_dup_mutex)) {
 62		if (strlen(kmod_req->name) == strlen(module_name) &&
 63		    !memcmp(kmod_req->name, module_name, strlen(module_name))) {
 64			return kmod_req;
 65                }
 66        }
 67
 68	return NULL;
 69}
 70
 71static void kmod_dup_request_delete(struct work_struct *work)
 72{
 73	struct kmod_dup_req *kmod_req;
 74	kmod_req = container_of(to_delayed_work(work), struct kmod_dup_req, delete_work);
 75
 76	/*
 77	 * The typical situation is a module successully loaded. In that
 78	 * situation the module will be present already in userspace. If
 79	 * new requests come in after that, userspace will already know the
 80	 * module is loaded so will just return 0 right away. There is still
 81	 * a small chance right after we delete this entry new request_module()
 82	 * calls may happen after that, they can happen. These heuristics
 83	 * are to protect finit_module() abuse for auto-loading, if modules
 84	 * are still tryign to auto-load even if a module is already loaded,
 85	 * that's on them, and those inneficiencies should not be fixed by
 86	 * kmod. The inneficies there are a call to modprobe and modprobe
 87	 * just returning 0.
 88	 */
 89	mutex_lock(&kmod_dup_mutex);
 90	list_del_rcu(&kmod_req->list);
 91	synchronize_rcu();
 92	mutex_unlock(&kmod_dup_mutex);
 93	kfree(kmod_req);
 94}
 95
 96static void kmod_dup_request_complete(struct work_struct *work)
 97{
 98	struct kmod_dup_req *kmod_req;
 99
100	kmod_req = container_of(work, struct kmod_dup_req, complete_work);
101
102	/*
103	 * This will ensure that the kernel will let all the waiters get
104	 * informed its time to check the return value. It's time to
105	 * go home.
106	 */
107	complete_all(&kmod_req->first_req_done);
108
109	/*
110	 * Now that we have allowed prior request_module() calls to go on
111	 * with life, let's schedule deleting this entry. We don't have
112	 * to do it right away, but we *eventually* want to do it so to not
113	 * let this linger forever as this is just a boot optimization for
114	 * possible abuses of vmalloc() incurred by finit_module() thrashing.
115	 */
116	queue_delayed_work(system_wq, &kmod_req->delete_work, 60 * HZ);
117}
118
119bool kmod_dup_request_exists_wait(char *module_name, bool wait, int *dup_ret)
120{
121	struct kmod_dup_req *kmod_req, *new_kmod_req;
122	int ret;
123
124	/*
125	 * Pre-allocate the entry in case we have to use it later
126	 * to avoid contention with the mutex.
127	 */
128	new_kmod_req = kzalloc(sizeof(*new_kmod_req), GFP_KERNEL);
129	if (!new_kmod_req)
130		return false;
131
132	memcpy(new_kmod_req->name, module_name, strlen(module_name));
133	INIT_WORK(&new_kmod_req->complete_work, kmod_dup_request_complete);
134	INIT_DELAYED_WORK(&new_kmod_req->delete_work, kmod_dup_request_delete);
135	init_completion(&new_kmod_req->first_req_done);
136
137	mutex_lock(&kmod_dup_mutex);
138
139	kmod_req = kmod_dup_request_lookup(module_name);
140	if (!kmod_req) {
141		/*
142		 * If the first request that came through for a module
143		 * was with request_module_nowait() we cannot wait for it
144		 * and share its return value with other users which may
145		 * have used request_module() and need a proper return value
146		 * so just skip using them as an anchor.
147		 *
148		 * If a prior request to this one came through with
149		 * request_module() though, then a request_module_nowait()
150		 * would benefit from duplicate detection.
151		 */
152		if (!wait) {
153			kfree(new_kmod_req);
154			pr_debug("New request_module_nowait() for %s -- cannot track duplicates for this request\n", module_name);
155			mutex_unlock(&kmod_dup_mutex);
156			return false;
157		}
158
159		/*
160		 * There was no duplicate, just add the request so we can
161		 * keep tab on duplicates later.
162		 */
163		pr_debug("New request_module() for %s\n", module_name);
164		list_add_rcu(&new_kmod_req->list, &dup_kmod_reqs);
165		mutex_unlock(&kmod_dup_mutex);
166		return false;
167	}
168	mutex_unlock(&kmod_dup_mutex);
169
170	/* We are dealing with a duplicate request now */
171	kfree(new_kmod_req);
172
173	/*
174	 * To fix these try to use try_then_request_module() instead as that
175	 * will check if the component you are looking for is present or not.
176	 * You could also just queue a single request to load the module once,
177	 * instead of having each and everything you need try to request for
178	 * the module.
179	 *
180	 * Duplicate request_module() calls  can cause quite a bit of wasted
181	 * vmalloc() space when racing with userspace.
182	 */
183	if (enable_dups_trace)
184		WARN(1, "module-autoload: duplicate request for module %s\n", module_name);
185	else
186		pr_warn("module-autoload: duplicate request for module %s\n", module_name);
187
188	if (!wait) {
189		/*
190		 * If request_module_nowait() was used then the user just
191		 * wanted to issue the request and if another module request
192		 * was already its way with the same name we don't care for
193		 * the return value either. Let duplicate request_module_nowait()
194		 * calls bail out right away.
195		 */
196		*dup_ret = 0;
197		return true;
198	}
199
200	/*
201	 * If a duplicate request_module() was used they *may* care for
202	 * the return value, so we have no other option but to wait for
203	 * the first caller to complete. If the first caller used
204	 * the request_module_nowait() call, subsquent callers will
205	 * deal with the comprmise of getting a successful call with this
206	 * optimization enabled ...
207	 */
208	ret = wait_for_completion_state(&kmod_req->first_req_done,
209					TASK_KILLABLE);
210	if (ret) {
211		*dup_ret = ret;
212		return true;
213	}
214
215	/* Now the duplicate request has the same exact return value as the first request */
216	*dup_ret = kmod_req->dup_ret;
217
218	return true;
219}
220
221void kmod_dup_request_announce(char *module_name, int ret)
222{
223	struct kmod_dup_req *kmod_req;
224
225	mutex_lock(&kmod_dup_mutex);
226
227	kmod_req = kmod_dup_request_lookup(module_name);
228	if (!kmod_req)
229		goto out;
230
231	kmod_req->dup_ret = ret;
232
233	/*
234	 * If we complete() here we may allow duplicate threads
235	 * to continue before the first one that submitted the
236	 * request. We're in no rush also, given that each and
237	 * every bounce back to userspace is slow we avoid that
238	 * with a slight delay here. So queueue up the completion
239	 * and let duplicates suffer, just wait a tad bit longer.
240	 * There is no rush. But we also don't want to hold the
241	 * caller up forever or introduce any boot delays.
242	 */
243	queue_work(system_wq, &kmod_req->complete_work);
244
245out:
246	mutex_unlock(&kmod_dup_mutex);
247}