kernel/capability.c

   1 /*
   2  * linux/kernel/capability.c
   3  *
   4  * Copyright (C) 1997  Andrew Main <zefram@fysh.org>
   5  *
   6  * Integrated into 2.1.97+,  Andrew G. Morgan <morgan@kernel.org>
   7  * 30 May 2002: Cleanup, Robert M. Love <rml@tech9.net>
   8  */
   9
  10 #include <linux/audit.h>
  11 #include <linux/capability.h>
  12 #include <linux/mm.h>
  13 #include <linux/module.h>
  14 #include <linux/security.h>
  15 #include <linux/syscalls.h>
  16 #include <linux/pid_namespace.h>
  17 #include <asm/uaccess.h>
  18 #include "cred-internals.h"
  19
  20 /*
  21  * Leveraged for setting/resetting capabilities
  22  */
  23
  24 const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
  25 const kernel_cap_t __cap_full_set = CAP_FULL_SET;
  26 const kernel_cap_t __cap_init_eff_set = CAP_INIT_EFF_SET;
  27
  28 EXPORT_SYMBOL(__cap_empty_set);
  29 EXPORT_SYMBOL(__cap_full_set);
  30 EXPORT_SYMBOL(__cap_init_eff_set);
  31
  32 int file_caps_enabled = 1;
  33
  34 static int __init file_caps_disable(char *str)
  35 {
  36         file_caps_enabled = 0;
  37         return 1;
  38 }
  39 __setup("no_file_caps", file_caps_disable);
  40
  41 /*
  42  * More recent versions of libcap are available from:
  43  *
  44  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  45  */
  46
  47 static void warn_legacy_capability_use(void)
  48 {
  49         static int warned;
  50         if (!warned) {
  51                 char name[sizeof(current->comm)];
  52
  53                 printk(KERN_INFO "warning: `%s' uses 32-bit capabilities"
  54                        " (legacy support in use)\n",
  55                        get_task_comm(name, current));
  56                 warned = 1;
  57         }
  58 }
  59
  60 /*
  61  * Version 2 capabilities worked fine, but the linux/capability.h file
  62  * that accompanied their introduction encouraged their use without
  63  * the necessary user-space source code changes. As such, we have
  64  * created a version 3 with equivalent functionality to version 2, but
  65  * with a header change to protect legacy source code from using
  66  * version 2 when it wanted to use version 1. If your system has code
  67  * that trips the following warning, it is using version 2 specific
  68  * capabilities and may be doing so insecurely.
  69  *
  70  * The remedy is to either upgrade your version of libcap (to 2.10+,
  71  * if the application is linked against it), or recompile your
  72  * application with modern kernel headers and this warning will go
  73  * away.
  74  */
  75
  76 static void warn_deprecated_v2(void)
  77 {
  78         static int warned;
  79
  80         if (!warned) {
  81                 char name[sizeof(current->comm)];
  82
  83                 printk(KERN_INFO "warning: `%s' uses deprecated v2"
  84                        " capabilities in a way that may be insecure.\n",
  85                        get_task_comm(name, current));
  86                 warned = 1;
  87         }
  88 }
  89
  90 /*
  91  * Version check. Return the number of u32s in each capability flag
  92  * array, or a negative value on error.
  93  */
  94 static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
  95 {
  96         __u32 version;
  97
  98         if (get_user(version, &header->version))
  99                 return -EFAULT;
 100
 101         switch (version) {
 102         case _LINUX_CAPABILITY_VERSION_1:
 103                 warn_legacy_capability_use();
 104                 *tocopy = _LINUX_CAPABILITY_U32S_1;
 105                 break;
 106         case _LINUX_CAPABILITY_VERSION_2:
 107                 warn_deprecated_v2();
 108                 /*
 109                  * fall through - v3 is otherwise equivalent to v2.
 110                  */
 111         case _LINUX_CAPABILITY_VERSION_3:
 112                 *tocopy = _LINUX_CAPABILITY_U32S_3;
 113                 break;
 114         default:
 115                 if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
 116                         return -EFAULT;
 117                 return -EINVAL;
 118         }
 119
 120         return 0;
 121 }
 122
 123 /*
 124  * The only thing that can change the capabilities of the current
 125  * process is the current process. As such, we can't be in this code
 126  * at the same time as we are in the process of setting capabilities
 127  * in this process. The net result is that we can limit our use of
 128  * locks to when we are reading the caps of another process.
 129  */
 130 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 131                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 132 {
 133         int ret;
 134
 135         if (pid && (pid != task_pid_vnr(current))) {
 136                 struct task_struct *target;
 137
 138                 rcu_read_lock();
 139
 140                 target = find_task_by_vpid(pid);
 141                 if (!target)
 142                         ret = -ESRCH;
 143                 else
 144                         ret = security_capget(target, pEp, pIp, pPp);
 145
 146                 rcu_read_unlock();
 147         } else
 148                 ret = security_capget(current, pEp, pIp, pPp);
 149
 150         return ret;
 151 }
 152
 153 /**
 154  * sys_capget - get the capabilities of a given process.
 155  * @header: pointer to struct that contains capability version and
 156  *      target pid data
 157  * @dataptr: pointer to struct that contains the effective, permitted,
 158  *      and inheritable capabilities that are returned
 159  *
 160  * Returns 0 on success and < 0 on error.
 161  */
 162 SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
 163 {
 164         int ret = 0;
 165         pid_t pid;
 166         unsigned tocopy;
 167         kernel_cap_t pE, pI, pP;
 168
 169         ret = cap_validate_magic(header, &tocopy);
 170         if ((dataptr == NULL) || (ret != 0))
 171                 return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : ret;
 172
 173         if (get_user(pid, &header->pid))
 174                 return -EFAULT;
 175
 176         if (pid < 0)
 177                 return -EINVAL;
 178
 179         ret = cap_get_target_pid(pid, &pE, &pI, &pP);
 180         if (!ret) {
 181                 struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 182                 unsigned i;
 183
 184                 for (i = 0; i < tocopy; i++) {
 185                         kdata[i].effective = pE.cap[i];
 186                         kdata[i].permitted = pP.cap[i];
 187                         kdata[i].inheritable = pI.cap[i];
 188                 }
 189
 190                 /*
 191                  * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
 192                  * we silently drop the upper capabilities here. This
 193                  * has the effect of making older libcap
 194                  * implementations implicitly drop upper capability
 195                  * bits when they perform a: capget/modify/capset
 196                  * sequence.
 197                  *
 198                  * This behavior is considered fail-safe
 199                  * behavior. Upgrading the application to a newer
 200                  * version of libcap will enable access to the newer
 201                  * capabilities.
 202                  *
 203                  * An alternative would be to return an error here
 204                  * (-ERANGE), but that causes legacy applications to
 205                  * unexpectidly fail; the capget/modify/capset aborts
 206                  * before modification is attempted and the application
 207                  * fails.
 208                  */
 209                 if (copy_to_user(dataptr, kdata, tocopy
 210                                  * sizeof(struct __user_cap_data_struct))) {
 211                         return -EFAULT;
 212                 }
 213         }
 214
 215         return ret;
 216 }
 217
 218 /**
 219  * sys_capset - set capabilities for a process or (*) a group of processes
 220  * @header: pointer to struct that contains capability version and
 221  *      target pid data
 222  * @data: pointer to struct that contains the effective, permitted,
 223  *      and inheritable capabilities
 224  *
 225  * Set capabilities for the current process only.  The ability to any other
 226  * process(es) has been deprecated and removed.
 227  *
 228  * The restrictions on setting capabilities are specified as:
 229  *
 230  * I: any raised capabilities must be a subset of the old permitted
 231  * P: any raised capabilities must be a subset of the old permitted
 232  * E: must be set to a subset of new permitted
 233  *
 234  * Returns 0 on success and < 0 on error.
 235  */
 236 SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
 237 {
 238         struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 239         unsigned i, tocopy, copybytes;
 240         kernel_cap_t inheritable, permitted, effective;
 241         struct cred *new;
 242         int ret;
 243         pid_t pid;
 244
 245         ret = cap_validate_magic(header, &tocopy);
 246         if (ret != 0)
 247                 return ret;
 248
 249         if (get_user(pid, &header->pid))
 250                 return -EFAULT;
 251
 252         /* may only affect current now */
 253         if (pid != 0 && pid != task_pid_vnr(current))
 254                 return -EPERM;
 255
 256         copybytes = tocopy * sizeof(struct __user_cap_data_struct);
 257         if (copybytes > sizeof(kdata))
 258                 return -EFAULT;
 259
 260         if (copy_from_user(&kdata, data, copybytes))
 261                 return -EFAULT;
 262
 263         for (i = 0; i < tocopy; i++) {
 264                 effective.cap[i] = kdata[i].effective;
 265                 permitted.cap[i] = kdata[i].permitted;
 266                 inheritable.cap[i] = kdata[i].inheritable;
 267         }
 268         while (i < _KERNEL_CAPABILITY_U32S) {
 269                 effective.cap[i] = 0;
 270                 permitted.cap[i] = 0;
 271                 inheritable.cap[i] = 0;
 272                 i++;
 273         }
 274
 275         new = prepare_creds();
 276         if (!new)
 277                 return -ENOMEM;
 278
 279         ret = security_capset(new, current_cred(),
 280                               &effective, &inheritable, &permitted);
 281         if (ret < 0)
 282                 goto error;
 283
 284         audit_log_capset(pid, new, current_cred());
 285
 286         return commit_creds(new);
 287
 288 error:
 289         abort_creds(new);
 290         return ret;
 291 }
 292
 293 /**
 294  * capable - Determine if the current task has a superior capability in effect
 295  * @cap: The capability to be tested for
 296  *
 297  * Return true if the current task has the given superior capability currently
 298  * available for use, false if not.
 299  *
 300  * This sets PF_SUPERPRIV on the task if the capability is available on the
 301  * assumption that it's about to be used.
 302  */
 303 int capable(int cap)
 304 {
 305         if (unlikely(!cap_valid(cap))) {
 306                 printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
 307                 BUG();
 308         }
 309
 310         if (security_capable(cap) == 0) {
 311                 current->flags |= PF_SUPERPRIV;
 312                 return 1;
 313         }
 314         return 0;
 315 }
 316 EXPORT_SYMBOL(capable);