fs/proc/proc_sysctl.c

   1 /*
   2  * /proc/sys support
   3  */
   4
   5 #include <linux/sysctl.h>
   6 #include <linux/proc_fs.h>
   7 #include <linux/security.h>
   8 #include "internal.h"
   9
  10 static struct dentry_operations proc_sys_dentry_operations;
  11 static const struct file_operations proc_sys_file_operations;
  12 static struct inode_operations proc_sys_inode_operations;
  13
  14 static void proc_sys_refresh_inode(struct inode *inode, struct ctl_table *table)
  15 {
  16         /* Refresh the cached information bits in the inode */
  17         if (table) {
  18                 inode->i_uid = 0;
  19                 inode->i_gid = 0;
  20                 inode->i_mode = table->mode;
  21                 if (table->proc_handler) {
  22                         inode->i_mode |= S_IFREG;
  23                         inode->i_nlink = 1;
  24                 } else {
  25                         inode->i_mode |= S_IFDIR;
  26                         inode->i_nlink = 0;     /* It is too hard to figure out */
  27                 }
  28         }
  29 }
  30
  31 static struct inode *proc_sys_make_inode(struct inode *dir, struct ctl_table *table)
  32 {
  33         struct inode *inode;
  34         struct proc_inode *dir_ei, *ei;
  35         int depth;
  36
  37         inode = new_inode(dir->i_sb);
  38         if (!inode)
  39                 goto out;
  40
  41         /* A directory is always one deeper than it's parent */
  42         dir_ei = PROC_I(dir);
  43         depth = dir_ei->fd + 1;
  44
  45         ei = PROC_I(inode);
  46         ei->fd = depth;
  47         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
  48         inode->i_op = &proc_sys_inode_operations;
  49         inode->i_fop = &proc_sys_file_operations;
  50         inode->i_flags |= S_PRIVATE; /* tell selinux to ignore this inode */
  51         proc_sys_refresh_inode(inode, table);
  52 out:
  53         return inode;
  54 }
  55
  56 static struct dentry *proc_sys_ancestor(struct dentry *dentry, int depth)
  57 {
  58         for (;;) {
  59                 struct proc_inode *ei;
  60
  61                 ei = PROC_I(dentry->d_inode);
  62                 if (ei->fd == depth)
  63                         break; /* found */
  64
  65                 dentry = dentry->d_parent;
  66         }
  67         return dentry;
  68 }
  69
  70 static struct ctl_table *proc_sys_lookup_table_one(struct ctl_table *table,
  71                                                         struct qstr *name)
  72 {
  73         int len;
  74         for ( ; table->ctl_name || table->procname; table++) {
  75
  76                 if (!table->procname)
  77                         continue;
  78
  79                 len = strlen(table->procname);
  80                 if (len != name->len)
  81                         continue;
  82
  83                 if (memcmp(table->procname, name->name, len) != 0)
  84                         continue;
  85
  86                 /* I have a match */
  87                 return table;
  88         }
  89         return NULL;
  90 }
  91
  92 static struct ctl_table *proc_sys_lookup_table(struct dentry *dentry,
  93                                                 struct ctl_table *table)
  94 {
  95         struct dentry *ancestor;
  96         struct proc_inode *ei;
  97         int depth, i;
  98
  99         ei = PROC_I(dentry->d_inode);
 100         depth = ei->fd;
 101
 102         if (depth == 0)
 103                 return table;
 104
 105         for (i = 1; table && (i <= depth); i++) {
 106                 ancestor = proc_sys_ancestor(dentry, i);
 107                 table = proc_sys_lookup_table_one(table, &ancestor->d_name);
 108                 if (table)
 109                         table = table->child;
 110         }
 111         return table;
 112
 113 }
 114 static struct ctl_table *proc_sys_lookup_entry(struct dentry *dparent,
 115                                                 struct qstr *name,
 116                                                 struct ctl_table *table)
 117 {
 118         table = proc_sys_lookup_table(dparent, table);
 119         if (table)
 120                 table = proc_sys_lookup_table_one(table, name);
 121         return table;
 122 }
 123
 124 static struct ctl_table *do_proc_sys_lookup(struct dentry *parent,
 125                                                 struct qstr *name,
 126                                                 struct ctl_table_header **ptr)
 127 {
 128         struct ctl_table_header *head;
 129         struct ctl_table *table = NULL;
 130
 131         for (head = sysctl_head_next(NULL); head;
 132                         head = sysctl_head_next(head)) {
 133                 table = proc_sys_lookup_entry(parent, name, head->ctl_table);
 134                 if (table)
 135                         break;
 136         }
 137         *ptr = head;
 138         return table;
 139 }
 140
 141 static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
 142                                         struct nameidata *nd)
 143 {
 144         struct ctl_table_header *head;
 145         struct inode *inode;
 146         struct dentry *err;
 147         struct ctl_table *table;
 148
 149         err = ERR_PTR(-ENOENT);
 150         table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 151         if (!table)
 152                 goto out;
 153
 154         err = ERR_PTR(-ENOMEM);
 155         inode = proc_sys_make_inode(dir, table);
 156         if (!inode)
 157                 goto out;
 158
 159         err = NULL;
 160         dentry->d_op = &proc_sys_dentry_operations;
 161         d_add(dentry, inode);
 162
 163 out:
 164         sysctl_head_finish(head);
 165         return err;
 166 }
 167
 168 static ssize_t proc_sys_read(struct file *filp, char __user *buf,
 169                                 size_t count, loff_t *ppos)
 170 {
 171         struct dentry *dentry = filp->f_dentry;
 172         struct ctl_table_header *head;
 173         struct ctl_table *table;
 174         ssize_t error, res;
 175
 176         table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 177         /* Has the sysctl entry disappeared on us? */
 178         error = -ENOENT;
 179         if (!table)
 180                 goto out;
 181
 182         /* Has the sysctl entry been replaced by a directory? */
 183         error = -EISDIR;
 184         if (!table->proc_handler)
 185                 goto out;
 186
 187         /*
 188          * At this point we know that the sysctl was not unregistered
 189          * and won't be until we finish.
 190          */
 191         error = -EPERM;
 192         if (sysctl_perm(table, MAY_READ))
 193                 goto out;
 194
 195         /* careful: calling conventions are nasty here */
 196         res = count;
 197         error = table->proc_handler(table, 0, filp, buf, &res, ppos);
 198         if (!error)
 199                 error = res;
 200 out:
 201         sysctl_head_finish(head);
 202
 203         return error;
 204 }
 205
 206 static ssize_t proc_sys_write(struct file *filp, const char __user *buf,
 207                                 size_t count, loff_t *ppos)
 208 {
 209         struct dentry *dentry = filp->f_dentry;
 210         struct ctl_table_header *head;
 211         struct ctl_table *table;
 212         ssize_t error, res;
 213
 214         table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 215         /* Has the sysctl entry disappeared on us? */
 216         error = -ENOENT;
 217         if (!table)
 218                 goto out;
 219
 220         /* Has the sysctl entry been replaced by a directory? */
 221         error = -EISDIR;
 222         if (!table->proc_handler)
 223                 goto out;
 224
 225         /*
 226          * At this point we know that the sysctl was not unregistered
 227          * and won't be until we finish.
 228          */
 229         error = -EPERM;
 230         if (sysctl_perm(table, MAY_WRITE))
 231                 goto out;
 232
 233         /* careful: calling conventions are nasty here */
 234         res = count;
 235         error = table->proc_handler(table, 1, filp, (char __user *)buf,
 236                                     &res, ppos);
 237         if (!error)
 238                 error = res;
 239 out:
 240         sysctl_head_finish(head);
 241
 242         return error;
 243 }
 244
 245
 246 static int proc_sys_fill_cache(struct file *filp, void *dirent,
 247                                 filldir_t filldir, struct ctl_table *table)
 248 {
 249         struct ctl_table_header *head;
 250         struct ctl_table *child_table = NULL;
 251         struct dentry *child, *dir = filp->f_path.dentry;
 252         struct inode *inode;
 253         struct qstr qname;
 254         ino_t ino = 0;
 255         unsigned type = DT_UNKNOWN;
 256         int ret;
 257
 258         qname.name = table->procname;
 259         qname.len  = strlen(table->procname);
 260         qname.hash = full_name_hash(qname.name, qname.len);
 261
 262         /* Suppress duplicates.
 263          * Only fill a directory entry if it is the value that
 264          * an ordinary lookup of that name returns.  Hide all
 265          * others.
 266          *
 267          * If we ever cache this translation in the dcache
 268          * I should do a dcache lookup first.  But for now
 269          * it is just simpler not to.
 270          */
 271         ret = 0;
 272         child_table = do_proc_sys_lookup(dir, &qname, &head);
 273         sysctl_head_finish(head);
 274         if (child_table != table)
 275                 return 0;
 276
 277         child = d_lookup(dir, &qname);
 278         if (!child) {
 279                 struct dentry *new;
 280                 new = d_alloc(dir, &qname);
 281                 if (new) {
 282                         inode = proc_sys_make_inode(dir->d_inode, table);
 283                         if (!inode)
 284                                 child = ERR_PTR(-ENOMEM);
 285                         else {
 286                                 new->d_op = &proc_sys_dentry_operations;
 287                                 d_add(new, inode);
 288                         }
 289                         if (child)
 290                                 dput(new);
 291                         else
 292                                 child = new;
 293                 }
 294         }
 295         if (!child || IS_ERR(child) || !child->d_inode)
 296                 goto end_instantiate;
 297         inode = child->d_inode;
 298         if (inode) {
 299                 ino  = inode->i_ino;
 300                 type = inode->i_mode >> 12;
 301         }
 302         dput(child);
 303 end_instantiate:
 304         if (!ino)
 305                 ino= find_inode_number(dir, &qname);
 306         if (!ino)
 307                 ino = 1;
 308         return filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
 309 }
 310
 311 static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
 312 {
 313         struct dentry *dentry = filp->f_dentry;
 314         struct inode *inode = dentry->d_inode;
 315         struct ctl_table_header *head = NULL;
 316         struct ctl_table *table;
 317         unsigned long pos;
 318         int ret;
 319
 320         ret = -ENOTDIR;
 321         if (!S_ISDIR(inode->i_mode))
 322                 goto out;
 323
 324         ret = 0;
 325         /* Avoid a switch here: arm builds fail with missing __cmpdi2 */
 326         if (filp->f_pos == 0) {
 327                 if (filldir(dirent, ".", 1, filp->f_pos,
 328                                 inode->i_ino, DT_DIR) < 0)
 329                         goto out;
 330                 filp->f_pos++;
 331         }
 332         if (filp->f_pos == 1) {
 333                 if (filldir(dirent, "..", 2, filp->f_pos,
 334                                 parent_ino(dentry), DT_DIR) < 0)
 335                         goto out;
 336                 filp->f_pos++;
 337         }
 338         pos = 2;
 339
 340         /* - Find each instance of the directory
 341          * - Read all entries in each instance
 342          * - Before returning an entry to user space lookup the entry
 343          *   by name and if I find a different entry don't return
 344          *   this one because it means it is a buried dup.
 345          * For sysctl this should only happen for directory entries.
 346          */
 347         for (head = sysctl_head_next(NULL); head; head = sysctl_head_next(head)) {
 348                 table = proc_sys_lookup_table(dentry, head->ctl_table);
 349
 350                 if (!table)
 351                         continue;
 352
 353                 for (; table->ctl_name || table->procname; table++, pos++) {
 354                         /* Can't do anything without a proc name */
 355                         if (!table->procname)
 356                                 continue;
 357
 358                         if (pos < filp->f_pos)
 359                                 continue;
 360
 361                         if (proc_sys_fill_cache(filp, dirent, filldir, table) < 0)
 362                                 goto out;
 363                         filp->f_pos = pos + 1;
 364                 }
 365         }
 366         ret = 1;
 367 out:
 368         sysctl_head_finish(head);
 369         return ret;
 370 }
 371
 372 static int proc_sys_permission(struct inode *inode, int mask, struct nameidata *nd)
 373 {
 374         /*
 375          * sysctl entries that are not writeable,
 376          * are _NOT_ writeable, capabilities or not.
 377          */
 378         struct ctl_table_header *head;
 379         struct ctl_table *table;
 380         struct dentry *dentry;
 381         int mode;
 382         int depth;
 383         int error;
 384
 385         head = NULL;
 386         depth = PROC_I(inode)->fd;
 387
 388         /* First check the cached permissions, in case we don't have
 389          * enough information to lookup the sysctl table entry.
 390          */
 391         error = -EACCES;
 392         mode = inode->i_mode;
 393
 394         if (current->euid == 0)
 395                 mode >>= 6;
 396         else if (in_group_p(0))
 397                 mode >>= 3;
 398
 399         if ((mode & mask & (MAY_READ|MAY_WRITE|MAY_EXEC)) == mask)
 400                 error = 0;
 401
 402         /* If we can't get a sysctl table entry the permission
 403          * checks on the cached mode will have to be enough.
 404          */
 405         if (!nd || !depth)
 406                 goto out;
 407
 408         dentry = nd->dentry;
 409         table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 410
 411         /* If the entry does not exist deny permission */
 412         error = -EACCES;
 413         if (!table)
 414                 goto out;
 415
 416         /* Use the permissions on the sysctl table entry */
 417         error = sysctl_perm(table, mask);
 418 out:
 419         sysctl_head_finish(head);
 420         return error;
 421 }
 422
 423 static int proc_sys_setattr(struct dentry *dentry, struct iattr *attr)
 424 {
 425         struct inode *inode = dentry->d_inode;
 426         int error;
 427
 428         if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 429                 return -EPERM;
 430
 431         error = inode_change_ok(inode, attr);
 432         if (!error)
 433                 error = inode_setattr(inode, attr);
 434
 435         return error;
 436 }
 437
 438 /* I'm lazy and don't distinguish between files and directories,
 439  * until access time.
 440  */
 441 static const struct file_operations proc_sys_file_operations = {
 442         .read           = proc_sys_read,
 443         .write          = proc_sys_write,
 444         .readdir        = proc_sys_readdir,
 445 };
 446
 447 static struct inode_operations proc_sys_inode_operations = {
 448         .lookup         = proc_sys_lookup,
 449         .permission     = proc_sys_permission,
 450         .setattr        = proc_sys_setattr,
 451 };
 452
 453 static int proc_sys_revalidate(struct dentry *dentry, struct nameidata *nd)
 454 {
 455         struct ctl_table_header *head;
 456         struct ctl_table *table;
 457         table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 458         proc_sys_refresh_inode(dentry->d_inode, table);
 459         sysctl_head_finish(head);
 460         return !!table;
 461 }
 462
 463 static struct dentry_operations proc_sys_dentry_operations = {
 464         .d_revalidate   = proc_sys_revalidate,
 465 };
 466
 467 static struct proc_dir_entry *proc_sys_root;
 468
 469 int proc_sys_init(void)
 470 {
 471         proc_sys_root = proc_mkdir("sys", NULL);
 472         proc_sys_root->proc_iops = &proc_sys_inode_operations;
 473         proc_sys_root->proc_fops = &proc_sys_file_operations;
 474         proc_sys_root->nlink = 0;
 475         return 0;
 476 }