kernel/utsname_sysctl.c

   1 /*
   2  *  Copyright (C) 2007
   3  *
   4  *  Author: Eric Biederman <ebiederm@xmision.com>
   5  *
   6  *  This program is free software; you can redistribute it and/or
   7  *  modify it under the terms of the GNU General Public License as
   8  *  published by the Free Software Foundation, version 2 of the
   9  *  License.
  10  */
  11
  12 #include <linux/export.h>
  13 #include <linux/uts.h>
  14 #include <linux/utsname.h>
  15 #include <linux/sysctl.h>
  16 #include <linux/wait.h>
  17
  18 #ifdef CONFIG_PROC_SYSCTL
  19
  20 static void *get_uts(struct ctl_table *table)
  21 {
  22         char *which = table->data;
  23         struct uts_namespace *uts_ns;
  24
  25         uts_ns = current->nsproxy->uts_ns;
  26         which = (which - (char *)&init_uts_ns) + (char *)uts_ns;
  27
  28         return which;
  29 }
  30
  31 /*
  32  *      Special case of dostring for the UTS structure. This has locks
  33  *      to observe. Should this be in kernel/sys.c ????
  34  */
  35 static int proc_do_uts_string(struct ctl_table *table, int write,
  36                   void __user *buffer, size_t *lenp, loff_t *ppos)
  37 {
  38         struct ctl_table uts_table;
  39         int r;
  40         char tmp_data[__NEW_UTS_LEN + 1];
  41
  42         memcpy(&uts_table, table, sizeof(uts_table));
  43         uts_table.data = tmp_data;
  44
  45         /*
  46          * Buffer the value in tmp_data so that proc_dostring() can be called
  47          * without holding any locks.
  48          * We also need to read the original value in the write==1 case to
  49          * support partial writes.
  50          */
  51         down_read(&uts_sem);
  52         memcpy(tmp_data, get_uts(table), sizeof(tmp_data));
  53         up_read(&uts_sem);
  54         r = proc_dostring(&uts_table, write, buffer, lenp, ppos);
  55
  56         if (write) {
  57                 /*
  58                  * Write back the new value.
  59                  * Note that, since we dropped uts_sem, the result can
  60                  * theoretically be incorrect if there are two parallel writes
  61                  * at non-zero offsets to the same sysctl.
  62                  */
  63                 down_write(&uts_sem);
  64                 memcpy(get_uts(table), tmp_data, sizeof(tmp_data));
  65                 up_write(&uts_sem);
  66                 proc_sys_poll_notify(table->poll);
  67         }
  68
  69         return r;
  70 }
  71 #else
  72 #define proc_do_uts_string NULL
  73 #endif
  74
  75 static DEFINE_CTL_TABLE_POLL(hostname_poll);
  76 static DEFINE_CTL_TABLE_POLL(domainname_poll);
  77
  78 static struct ctl_table uts_kern_table[] = {
  79         {
  80                 .procname       = "ostype",
  81                 .data           = init_uts_ns.name.sysname,
  82                 .maxlen         = sizeof(init_uts_ns.name.sysname),
  83                 .mode           = 0444,
  84                 .proc_handler   = proc_do_uts_string,
  85         },
  86         {
  87                 .procname       = "osrelease",
  88                 .data           = init_uts_ns.name.release,
  89                 .maxlen         = sizeof(init_uts_ns.name.release),
  90                 .mode           = 0444,
  91                 .proc_handler   = proc_do_uts_string,
  92         },
  93         {
  94                 .procname       = "version",
  95                 .data           = init_uts_ns.name.version,
  96                 .maxlen         = sizeof(init_uts_ns.name.version),
  97                 .mode           = 0444,
  98                 .proc_handler   = proc_do_uts_string,
  99         },
 100         {
 101                 .procname       = "hostname",
 102                 .data           = init_uts_ns.name.nodename,
 103                 .maxlen         = sizeof(init_uts_ns.name.nodename),
 104                 .mode           = 0644,
 105                 .proc_handler   = proc_do_uts_string,
 106                 .poll           = &hostname_poll,
 107         },
 108         {
 109                 .procname       = "domainname",
 110                 .data           = init_uts_ns.name.domainname,
 111                 .maxlen         = sizeof(init_uts_ns.name.domainname),
 112                 .mode           = 0644,
 113                 .proc_handler   = proc_do_uts_string,
 114                 .poll           = &domainname_poll,
 115         },
 116         {}
 117 };
 118
 119 static struct ctl_table uts_root_table[] = {
 120         {
 121                 .procname       = "kernel",
 122                 .mode           = 0555,
 123                 .child          = uts_kern_table,
 124         },
 125         {}
 126 };
 127
 128 #ifdef CONFIG_PROC_SYSCTL
 129 /*
 130  * Notify userspace about a change in a certain entry of uts_kern_table,
 131  * identified by the parameter proc.
 132  */
 133 void uts_proc_notify(enum uts_proc proc)
 134 {
 135         struct ctl_table *table = &uts_kern_table[proc];
 136
 137         proc_sys_poll_notify(table->poll);
 138 }
 139 #endif
 140
 141 static int __init utsname_sysctl_init(void)
 142 {
 143         register_sysctl_table(uts_root_table);
 144         return 0;
 145 }
 146
 147 device_initcall(utsname_sysctl_init);