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