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Linux/kernel/kmod.c

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  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  * becomes a no-operation.
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 0;
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);
179 

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