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