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