/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* kmod dups - the kernel module autoloader duplicate suppressor
*
* Copyright (C) 2023 Luis Chamberlain <[email protected]>
*/
#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_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);
}
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