/* 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/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_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);}