kernel/utsname_sysctl.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  Copyright (C) 2007
   4  *
   5  *  Author: Eric Biederman <ebiederm@xmision.com>
   6  */
   7
   8 #include <linux/export.h>
   9 #include <linux/uts.h>
  10 #include <linux/utsname.h>
  11 #include <linux/random.h>
  12 #include <linux/sysctl.h>
  13 #include <linux/wait.h>
  14 #include <linux/rwsem.h>
  15
  16 #ifdef CONFIG_PROC_SYSCTL
  17
  18 static void *get_uts(const struct ctl_table *table)
  19 {
  20         char *which = table->data;
  21         struct uts_namespace *uts_ns;
  22
  23         uts_ns = current->nsproxy->uts_ns;
  24         which = (which - (char *)&init_uts_ns) + (char *)uts_ns;
  25
  26         return which;
  27 }
  28
  29 /*
  30  *      Special case of dostring for the UTS structure. This has locks
  31  *      to observe. Should this be in kernel/sys.c ????
  32  */
  33 static int proc_do_uts_string(const struct ctl_table *table, int write,
  34                   void *buffer, size_t *lenp, loff_t *ppos)
  35 {
  36         struct ctl_table uts_table;
  37         int r;
  38         char tmp_data[__NEW_UTS_LEN + 1];
  39
  40         memcpy(&uts_table, table, sizeof(uts_table));
  41         uts_table.data = tmp_data;
  42
  43         /*
  44          * Buffer the value in tmp_data so that proc_dostring() can be called
  45          * without holding any locks.
  46          * We also need to read the original value in the write==1 case to
  47          * support partial writes.
  48          */
  49         down_read(&uts_sem);
  50         memcpy(tmp_data, get_uts(table), sizeof(tmp_data));
  51         up_read(&uts_sem);
  52         r = proc_dostring(&uts_table, write, buffer, lenp, ppos);
  53
  54         if (write) {
  55                 /*
  56                  * Write back the new value.
  57                  * Note that, since we dropped uts_sem, the result can
  58                  * theoretically be incorrect if there are two parallel writes
  59                  * at non-zero offsets to the same sysctl.
  60                  */
  61                 add_device_randomness(tmp_data, sizeof(tmp_data));
  62                 down_write(&uts_sem);
  63                 memcpy(get_uts(table), tmp_data, sizeof(tmp_data));
  64                 up_write(&uts_sem);
  65                 proc_sys_poll_notify(table->poll);
  66         }
  67
  68         return r;
  69 }
  70 #else
  71 #define proc_do_uts_string NULL
  72 #endif
  73
  74 static DEFINE_CTL_TABLE_POLL(hostname_poll);
  75 static DEFINE_CTL_TABLE_POLL(domainname_poll);
  76
  77 // Note: update 'enum uts_proc' to match any changes to this table
  78 static struct ctl_table uts_kern_table[] = {
  79         {
  80                 .procname       = "arch",
  81                 .data           = init_uts_ns.name.machine,
  82                 .maxlen         = sizeof(init_uts_ns.name.machine),
  83                 .mode           = 0444,
  84                 .proc_handler   = proc_do_uts_string,
  85         },
  86         {
  87                 .procname       = "ostype",
  88                 .data           = init_uts_ns.name.sysname,
  89                 .maxlen         = sizeof(init_uts_ns.name.sysname),
  90                 .mode           = 0444,
  91                 .proc_handler   = proc_do_uts_string,
  92         },
  93         {
  94                 .procname       = "osrelease",
  95                 .data           = init_uts_ns.name.release,
  96                 .maxlen         = sizeof(init_uts_ns.name.release),
  97                 .mode           = 0444,
  98                 .proc_handler   = proc_do_uts_string,
  99         },
 100         {
 101                 .procname       = "version",
 102                 .data           = init_uts_ns.name.version,
 103                 .maxlen         = sizeof(init_uts_ns.name.version),
 104                 .mode           = 0444,
 105                 .proc_handler   = proc_do_uts_string,
 106         },
 107         {
 108                 .procname       = "hostname",
 109                 .data           = init_uts_ns.name.nodename,
 110                 .maxlen         = sizeof(init_uts_ns.name.nodename),
 111                 .mode           = 0644,
 112                 .proc_handler   = proc_do_uts_string,
 113                 .poll           = &hostname_poll,
 114         },
 115         {
 116                 .procname       = "domainname",
 117                 .data           = init_uts_ns.name.domainname,
 118                 .maxlen         = sizeof(init_uts_ns.name.domainname),
 119                 .mode           = 0644,
 120                 .proc_handler   = proc_do_uts_string,
 121                 .poll           = &domainname_poll,
 122         },
 123 };
 124
 125 #ifdef CONFIG_PROC_SYSCTL
 126 /*
 127  * Notify userspace about a change in a certain entry of uts_kern_table,
 128  * identified by the parameter proc.
 129  */
 130 void uts_proc_notify(enum uts_proc proc)
 131 {
 132         struct ctl_table *table = &uts_kern_table[proc];
 133
 134         proc_sys_poll_notify(table->poll);
 135 }
 136 #endif
 137
 138 static int __init utsname_sysctl_init(void)
 139 {
 140         register_sysctl("kernel", uts_kern_table);
 141         return 0;
 142 }
 143
 144 device_initcall(utsname_sysctl_init);