kernel/module/dups.c

   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."
  38 static bool enable_dups_trace = IS_ENABLED(CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS_TRACE);
  39 module_param(enable_dups_trace, bool_enable_only, 0644);
  40
  41 /*
  42  * Protects dup_kmod_reqs list, adds / removals with RCU.
  43  */
  44 static DEFINE_MUTEX(kmod_dup_mutex);
  45 static LIST_HEAD(dup_kmod_reqs);
  46
  47 struct 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
  56 static 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
  71 static 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
  96 static 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
 119 bool 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
 221 void 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
 245 out:
 246         mutex_unlock(&kmod_dup_mutex);
 247 }