kernel/kmod.c

   1 /*
   2  * kmod - the kernel module loader
   3  */
   4 #include <linux/module.h>
   5 #include <linux/sched.h>
   6 #include <linux/sched/task.h>
   7 #include <linux/binfmts.h>
   8 #include <linux/syscalls.h>
   9 #include <linux/unistd.h>
  10 #include <linux/kmod.h>
  11 #include <linux/slab.h>
  12 #include <linux/completion.h>
  13 #include <linux/cred.h>
  14 #include <linux/file.h>
  15 #include <linux/fdtable.h>
  16 #include <linux/workqueue.h>
  17 #include <linux/security.h>
  18 #include <linux/mount.h>
  19 #include <linux/kernel.h>
  20 #include <linux/init.h>
  21 #include <linux/resource.h>
  22 #include <linux/notifier.h>
  23 #include <linux/suspend.h>
  24 #include <linux/rwsem.h>
  25 #include <linux/ptrace.h>
  26 #include <linux/async.h>
  27 #include <linux/uaccess.h>
  28
  29 #include <trace/events/module.h>
  30
  31 /*
  32  * Assuming:
  33  *
  34  * threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE,
  35  *                     (u64) THREAD_SIZE * 8UL);
  36  *
  37  * If you need less than 50 threads would mean we're dealing with systems
  38  * smaller than 3200 pages. This assumes you are capable of having ~13M memory,
  39  * and this would only be an upper limit, after which the OOM killer would take
  40  * effect. Systems like these are very unlikely if modules are enabled.
  41  */
  42 #define MAX_KMOD_CONCURRENT 50
  43 static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT);
  44 static DECLARE_WAIT_QUEUE_HEAD(kmod_wq);
  45
  46 /*
  47  * This is a restriction on having *all* MAX_KMOD_CONCURRENT threads
  48  * running at the same time without returning. When this happens we
  49  * believe you've somehow ended up with a recursive module dependency
  50  * creating a loop.
  51  *
  52  * We have no option but to fail.
  53  *
  54  * Userspace should proactively try to detect and prevent these.
  55  */
  56 #define MAX_KMOD_ALL_BUSY_TIMEOUT 5
  57
  58 /*
  59         modprobe_path is set via /proc/sys.
  60 */
  61 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  62
  63 static void free_modprobe_argv(struct subprocess_info *info)
  64 {
  65         kfree(info->argv[3]); /* check call_modprobe() */
  66         kfree(info->argv);
  67 }
  68
  69 static int call_modprobe(char *module_name, int wait)
  70 {
  71         struct subprocess_info *info;
  72         static char *envp[] = {
  73                 "HOME=/",
  74                 "TERM=linux",
  75                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  76                 NULL
  77         };
  78
  79         char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
  80         if (!argv)
  81                 goto out;
  82
  83         module_name = kstrdup(module_name, GFP_KERNEL);
  84         if (!module_name)
  85                 goto free_argv;
  86
  87         argv[0] = modprobe_path;
  88         argv[1] = "-q";
  89         argv[2] = "--";
  90         argv[3] = module_name;  /* check free_modprobe_argv() */
  91         argv[4] = NULL;
  92
  93         info = call_usermodehelper_setup(modprobe_path, argv, envp, GFP_KERNEL,
  94                                          NULL, free_modprobe_argv, NULL);
  95         if (!info)
  96                 goto free_module_name;
  97
  98         return call_usermodehelper_exec(info, wait | UMH_KILLABLE);
  99
 100 free_module_name:
 101         kfree(module_name);
 102 free_argv:
 103         kfree(argv);
 104 out:
 105         return -ENOMEM;
 106 }
 107
 108 /**
 109  * __request_module - try to load a kernel module
 110  * @wait: wait (or not) for the operation to complete
 111  * @fmt: printf style format string for the name of the module
 112  * @...: arguments as specified in the format string
 113  *
 114  * Load a module using the user mode module loader. The function returns
 115  * zero on success or a negative errno code or positive exit code from
 116  * "modprobe" on failure. Note that a successful module load does not mean
 117  * the module did not then unload and exit on an error of its own. Callers
 118  * must check that the service they requested is now available not blindly
 119  * invoke it.
 120  *
 121  * If module auto-loading support is disabled then this function
 122  * simply returns -ENOENT.
 123  */
 124 int __request_module(bool wait, const char *fmt, ...)
 125 {
 126         va_list args;
 127         char module_name[MODULE_NAME_LEN];
 128         int ret;
 129
 130         /*
 131          * We don't allow synchronous module loading from async.  Module
 132          * init may invoke async_synchronize_full() which will end up
 133          * waiting for this task which already is waiting for the module
 134          * loading to complete, leading to a deadlock.
 135          */
 136         WARN_ON_ONCE(wait && current_is_async());
 137
 138         if (!modprobe_path[0])
 139                 return -ENOENT;
 140
 141         va_start(args, fmt);
 142         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
 143         va_end(args);
 144         if (ret >= MODULE_NAME_LEN)
 145                 return -ENAMETOOLONG;
 146
 147         ret = security_kernel_module_request(module_name);
 148         if (ret)
 149                 return ret;
 150
 151         if (atomic_dec_if_positive(&kmod_concurrent_max) < 0) {
 152                 pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s, throttling...",
 153                                     atomic_read(&kmod_concurrent_max),
 154                                     MAX_KMOD_CONCURRENT, module_name);
 155                 ret = wait_event_killable_timeout(kmod_wq,
 156                                                   atomic_dec_if_positive(&kmod_concurrent_max) >= 0,
 157                                                   MAX_KMOD_ALL_BUSY_TIMEOUT * HZ);
 158                 if (!ret) {
 159                         pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
 160                                             module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
 161                         return -ETIME;
 162                 } else if (ret == -ERESTARTSYS) {
 163                         pr_warn_ratelimited("request_module: sigkill sent for modprobe %s, giving up", module_name);
 164                         return ret;
 165                 }
 166         }
 167
 168         trace_module_request(module_name, wait, _RET_IP_);
 169
 170         ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
 171
 172         atomic_inc(&kmod_concurrent_max);
 173         wake_up(&kmod_wq);
 174
 175         return ret;
 176 }
 177 EXPORT_SYMBOL(__request_module);