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 #ifdef CONFIG_SECURITY_FILE_CAPABILITIES
  33 int file_caps_enabled = 1;
  34
  35 static int __init file_caps_disable(char *str)
  36 {
  37         file_caps_enabled = 0;
  38         return 1;
  39 }
  40 __setup("no_file_caps", file_caps_disable);
  41 #endif
  42
  43 /*
  44  * More recent versions of libcap are available from:
  45  *
  46  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  47  */
  48
  49 static void warn_legacy_capability_use(void)
  50 {
  51         static int warned;
  52         if (!warned) {
  53                 char name[sizeof(current->comm)];
  54
  55                 printk(KERN_INFO "warning: `%s' uses 32-bit capabilities"
  56                        " (legacy support in use)\n",
  57                        get_task_comm(name, current));
  58                 warned = 1;
  59         }
  60 }
  61
  62 /*
  63  * Version 2 capabilities worked fine, but the linux/capability.h file
  64  * that accompanied their introduction encouraged their use without
  65  * the necessary user-space source code changes. As such, we have
  66  * created a version 3 with equivalent functionality to version 2, but
  67  * with a header change to protect legacy source code from using
  68  * version 2 when it wanted to use version 1. If your system has code
  69  * that trips the following warning, it is using version 2 specific
  70  * capabilities and may be doing so insecurely.
  71  *
  72  * The remedy is to either upgrade your version of libcap (to 2.10+,
  73  * if the application is linked against it), or recompile your
  74  * application with modern kernel headers and this warning will go
  75  * away.
  76  */
  77
  78 static void warn_deprecated_v2(void)
  79 {
  80         static int warned;
  81
  82         if (!warned) {
  83                 char name[sizeof(current->comm)];
  84
  85                 printk(KERN_INFO "warning: `%s' uses deprecated v2"
  86                        " capabilities in a way that may be insecure.\n",
  87                        get_task_comm(name, current));
  88                 warned = 1;
  89         }
  90 }
  91
  92 /*
  93  * Version check. Return the number of u32s in each capability flag
  94  * array, or a negative value on error.
  95  */
  96 static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
  97 {
  98         __u32 version;
  99
 100         if (get_user(version, &header->version))
 101                 return -EFAULT;
 102
 103         switch (version) {
 104         case _LINUX_CAPABILITY_VERSION_1:
 105                 warn_legacy_capability_use();
 106                 *tocopy = _LINUX_CAPABILITY_U32S_1;
 107                 break;
 108         case _LINUX_CAPABILITY_VERSION_2:
 109                 warn_deprecated_v2();
 110                 /*
 111                  * fall through - v3 is otherwise equivalent to v2.
 112                  */
 113         case _LINUX_CAPABILITY_VERSION_3:
 114                 *tocopy = _LINUX_CAPABILITY_U32S_3;
 115                 break;
 116         default:
 117                 if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
 118                         return -EFAULT;
 119                 return -EINVAL;
 120         }
 121
 122         return 0;
 123 }
 124
 125 /*
 126  * The only thing that can change the capabilities of the current
 127  * process is the current process. As such, we can't be in this code
 128  * at the same time as we are in the process of setting capabilities
 129  * in this process. The net result is that we can limit our use of
 130  * locks to when we are reading the caps of another process.
 131  */
 132 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 133                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 134 {
 135         int ret;
 136
 137         if (pid && (pid != task_pid_vnr(current))) {
 138                 struct task_struct *target;
 139
 140                 read_lock(&tasklist_lock);
 141
 142                 target = find_task_by_vpid(pid);
 143                 if (!target)
 144                         ret = -ESRCH;
 145                 else
 146                         ret = security_capget(target, pEp, pIp, pPp);
 147
 148                 read_unlock(&tasklist_lock);
 149         } else
 150                 ret = security_capget(current, pEp, pIp, pPp);
 151
 152         return ret;
 153 }
 154
 155 /**
 156  * sys_capget - get the capabilities of a given process.
 157  * @header: pointer to struct that contains capability version and
 158  *      target pid data
 159  * @dataptr: pointer to struct that contains the effective, permitted,
 160  *      and inheritable capabilities that are returned
 161  *
 162  * Returns 0 on success and < 0 on error.
 163  */
 164 SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
 165 {
 166         int ret = 0;
 167         pid_t pid;
 168         unsigned tocopy;
 169         kernel_cap_t pE, pI, pP;
 170
 171         ret = cap_validate_magic(header, &tocopy);
 172         if (ret != 0)
 173                 return ret;
 174
 175         if (get_user(pid, &header->pid))
 176                 return -EFAULT;
 177
 178         if (pid < 0)
 179                 return -EINVAL;
 180
 181         ret = cap_get_target_pid(pid, &pE, &pI, &pP);
 182         if (!ret) {
 183                 struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 184                 unsigned i;
 185
 186                 for (i = 0; i < tocopy; i++) {
 187                         kdata[i].effective = pE.cap[i];
 188                         kdata[i].permitted = pP.cap[i];
 189                         kdata[i].inheritable = pI.cap[i];
 190                 }
 191
 192                 /*
 193                  * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
 194                  * we silently drop the upper capabilities here. This
 195                  * has the effect of making older libcap
 196                  * implementations implicitly drop upper capability
 197                  * bits when they perform a: capget/modify/capset
 198                  * sequence.
 199                  *
 200                  * This behavior is considered fail-safe
 201                  * behavior. Upgrading the application to a newer
 202                  * version of libcap will enable access to the newer
 203                  * capabilities.
 204                  *
 205                  * An alternative would be to return an error here
 206                  * (-ERANGE), but that causes legacy applications to
 207                  * unexpectidly fail; the capget/modify/capset aborts
 208                  * before modification is attempted and the application
 209                  * fails.
 210                  */
 211                 if (copy_to_user(dataptr, kdata, tocopy
 212                                  * sizeof(struct __user_cap_data_struct))) {
 213                         return -EFAULT;
 214                 }
 215         }
 216
 217         return ret;
 218 }
 219
 220 /**
 221  * sys_capset - set capabilities for a process or (*) a group of processes
 222  * @header: pointer to struct that contains capability version and
 223  *      target pid data
 224  * @data: pointer to struct that contains the effective, permitted,
 225  *      and inheritable capabilities
 226  *
 227  * Set capabilities for the current process only.  The ability to any other
 228  * process(es) has been deprecated and removed.
 229  *
 230  * The restrictions on setting capabilities are specified as:
 231  *
 232  * I: any raised capabilities must be a subset of the old permitted
 233  * P: any raised capabilities must be a subset of the old permitted
 234  * E: must be set to a subset of new permitted
 235  *
 236  * Returns 0 on success and < 0 on error.
 237  */
 238 SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
 239 {
 240         struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 241         unsigned i, tocopy, copybytes;
 242         kernel_cap_t inheritable, permitted, effective;
 243         struct cred *new;
 244         int ret;
 245         pid_t pid;
 246
 247         ret = cap_validate_magic(header, &tocopy);
 248         if (ret != 0)
 249                 return ret;
 250
 251         if (get_user(pid, &header->pid))
 252                 return -EFAULT;
 253
 254         /* may only affect current now */
 255         if (pid != 0 && pid != task_pid_vnr(current))
 256                 return -EPERM;
 257
 258         copybytes = tocopy * sizeof(struct __user_cap_data_struct);
 259         if (copybytes > sizeof(kdata))
 260                 return -EFAULT;
 261
 262         if (copy_from_user(&kdata, data, copybytes))
 263                 return -EFAULT;
 264
 265         for (i = 0; i < tocopy; i++) {
 266                 effective.cap[i] = kdata[i].effective;
 267                 permitted.cap[i] = kdata[i].permitted;
 268                 inheritable.cap[i] = kdata[i].inheritable;
 269         }
 270         while (i < _KERNEL_CAPABILITY_U32S) {
 271                 effective.cap[i] = 0;
 272                 permitted.cap[i] = 0;
 273                 inheritable.cap[i] = 0;
 274                 i++;
 275         }
 276
 277         new = prepare_creds();
 278         if (!new)
 279                 return -ENOMEM;
 280
 281         ret = security_capset(new, current_cred(),
 282                               &effective, &inheritable, &permitted);
 283         if (ret < 0)
 284                 goto error;
 285
 286         audit_log_capset(pid, new, current_cred());
 287
 288         return commit_creds(new);
 289
 290 error:
 291         abort_creds(new);
 292         return ret;
 293 }
 294
 295 /**
 296  * capable - Determine if the current task has a superior capability in effect
 297  * @cap: The capability to be tested for
 298  *
 299  * Return true if the current task has the given superior capability currently
 300  * available for use, false if not.
 301  *
 302  * This sets PF_SUPERPRIV on the task if the capability is available on the
 303  * assumption that it's about to be used.
 304  */
 305 int capable(int cap)
 306 {
 307         if (unlikely(!cap_valid(cap))) {
 308                 printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
 309                 BUG();
 310         }
 311
 312         if (security_capable(cap) == 0) {
 313                 current->flags |= PF_SUPERPRIV;
 314                 return 1;
 315         }
 316         return 0;
 317 }
 318 EXPORT_SYMBOL(capable);