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