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 const 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_call_handler(struct file *filp, void __user *buf,
 169                 size_t count, loff_t *ppos, int write)
 170 {
 171         struct dentry *dentry = filp->f_dentry;
 172         struct ctl_table_header *head;
 173         struct ctl_table *table;
 174         ssize_t error;
 175         size_t res;
 176
 177         table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 178         /* Has the sysctl entry disappeared on us? */
 179         error = -ENOENT;
 180         if (!table)
 181                 goto out;
 182
 183         /* Has the sysctl entry been replaced by a directory? */
 184         error = -EISDIR;
 185         if (!table->proc_handler)
 186                 goto out;
 187
 188         /*
 189          * At this point we know that the sysctl was not unregistered
 190          * and won't be until we finish.
 191          */
 192         error = -EPERM;
 193         if (sysctl_perm(head->root, table, write ? MAY_WRITE : MAY_READ))
 194                 goto out;
 195
 196         /* careful: calling conventions are nasty here */
 197         res = count;
 198         error = table->proc_handler(table, write, filp, buf, &res, ppos);
 199         if (!error)
 200                 error = res;
 201 out:
 202         sysctl_head_finish(head);
 203
 204         return error;
 205 }
 206
 207 static ssize_t proc_sys_read(struct file *filp, char __user *buf,
 208                                 size_t count, loff_t *ppos)
 209 {
 210         return proc_sys_call_handler(filp, (void __user *)buf, count, ppos, 0);
 211 }
 212
 213 static ssize_t proc_sys_write(struct file *filp, const char __user *buf,
 214                                 size_t count, loff_t *ppos)
 215 {
 216         return proc_sys_call_handler(filp, (void __user *)buf, count, ppos, 1);
 217 }
 218
 219
 220 static int proc_sys_fill_cache(struct file *filp, void *dirent,
 221                                 filldir_t filldir, struct ctl_table *table)
 222 {
 223         struct ctl_table_header *head;
 224         struct ctl_table *child_table = NULL;
 225         struct dentry *child, *dir = filp->f_path.dentry;
 226         struct inode *inode;
 227         struct qstr qname;
 228         ino_t ino = 0;
 229         unsigned type = DT_UNKNOWN;
 230         int ret;
 231
 232         qname.name = table->procname;
 233         qname.len  = strlen(table->procname);
 234         qname.hash = full_name_hash(qname.name, qname.len);
 235
 236         /* Suppress duplicates.
 237          * Only fill a directory entry if it is the value that
 238          * an ordinary lookup of that name returns.  Hide all
 239          * others.
 240          *
 241          * If we ever cache this translation in the dcache
 242          * I should do a dcache lookup first.  But for now
 243          * it is just simpler not to.
 244          */
 245         ret = 0;
 246         child_table = do_proc_sys_lookup(dir, &qname, &head);
 247         sysctl_head_finish(head);
 248         if (child_table != table)
 249                 return 0;
 250
 251         child = d_lookup(dir, &qname);
 252         if (!child) {
 253                 struct dentry *new;
 254                 new = d_alloc(dir, &qname);
 255                 if (new) {
 256                         inode = proc_sys_make_inode(dir->d_inode, table);
 257                         if (!inode)
 258                                 child = ERR_PTR(-ENOMEM);
 259                         else {
 260                                 new->d_op = &proc_sys_dentry_operations;
 261                                 d_add(new, inode);
 262                         }
 263                         if (child)
 264                                 dput(new);
 265                         else
 266                                 child = new;
 267                 }
 268         }
 269         if (!child || IS_ERR(child) || !child->d_inode)
 270                 goto end_instantiate;
 271         inode = child->d_inode;
 272         if (inode) {
 273                 ino  = inode->i_ino;
 274                 type = inode->i_mode >> 12;
 275         }
 276         dput(child);
 277 end_instantiate:
 278         if (!ino)
 279                 ino= find_inode_number(dir, &qname);
 280         if (!ino)
 281                 ino = 1;
 282         return filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
 283 }
 284
 285 static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
 286 {
 287         struct dentry *dentry = filp->f_dentry;
 288         struct inode *inode = dentry->d_inode;
 289         struct ctl_table_header *head = NULL;
 290         struct ctl_table *table;
 291         unsigned long pos;
 292         int ret;
 293
 294         ret = -ENOTDIR;
 295         if (!S_ISDIR(inode->i_mode))
 296                 goto out;
 297
 298         ret = 0;
 299         /* Avoid a switch here: arm builds fail with missing __cmpdi2 */
 300         if (filp->f_pos == 0) {
 301                 if (filldir(dirent, ".", 1, filp->f_pos,
 302                                 inode->i_ino, DT_DIR) < 0)
 303                         goto out;
 304                 filp->f_pos++;
 305         }
 306         if (filp->f_pos == 1) {
 307                 if (filldir(dirent, "..", 2, filp->f_pos,
 308                                 parent_ino(dentry), DT_DIR) < 0)
 309                         goto out;
 310                 filp->f_pos++;
 311         }
 312         pos = 2;
 313
 314         /* - Find each instance of the directory
 315          * - Read all entries in each instance
 316          * - Before returning an entry to user space lookup the entry
 317          *   by name and if I find a different entry don't return
 318          *   this one because it means it is a buried dup.
 319          * For sysctl this should only happen for directory entries.
 320          */
 321         for (head = sysctl_head_next(NULL); head; head = sysctl_head_next(head)) {
 322                 table = proc_sys_lookup_table(dentry, head->ctl_table);
 323
 324                 if (!table)
 325                         continue;
 326
 327                 for (; table->ctl_name || table->procname; table++, pos++) {
 328                         /* Can't do anything without a proc name */
 329                         if (!table->procname)
 330                                 continue;
 331
 332                         if (pos < filp->f_pos)
 333                                 continue;
 334
 335                         if (proc_sys_fill_cache(filp, dirent, filldir, table) < 0)
 336                                 goto out;
 337                         filp->f_pos = pos + 1;
 338                 }
 339         }
 340         ret = 1;
 341 out:
 342         sysctl_head_finish(head);
 343         return ret;
 344 }
 345
 346 static int proc_sys_permission(struct inode *inode, int mask, struct nameidata *nd)
 347 {
 348         /*
 349          * sysctl entries that are not writeable,
 350          * are _NOT_ writeable, capabilities or not.
 351          */
 352         struct ctl_table_header *head;
 353         struct ctl_table *table;
 354         struct dentry *dentry;
 355         int mode;
 356         int depth;
 357         int error;
 358
 359         head = NULL;
 360         depth = PROC_I(inode)->fd;
 361
 362         /* First check the cached permissions, in case we don't have
 363          * enough information to lookup the sysctl table entry.
 364          */
 365         error = -EACCES;
 366         mode = inode->i_mode;
 367
 368         if (current->euid == 0)
 369                 mode >>= 6;
 370         else if (in_group_p(0))
 371                 mode >>= 3;
 372
 373         if ((mode & mask & (MAY_READ|MAY_WRITE|MAY_EXEC)) == mask)
 374                 error = 0;
 375
 376         /* If we can't get a sysctl table entry the permission
 377          * checks on the cached mode will have to be enough.
 378          */
 379         if (!nd || !depth)
 380                 goto out;
 381
 382         dentry = nd->path.dentry;
 383         table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 384
 385         /* If the entry does not exist deny permission */
 386         error = -EACCES;
 387         if (!table)
 388                 goto out;
 389
 390         /* Use the permissions on the sysctl table entry */
 391         error = sysctl_perm(head->root, table, mask);
 392 out:
 393         sysctl_head_finish(head);
 394         return error;
 395 }
 396
 397 static int proc_sys_setattr(struct dentry *dentry, struct iattr *attr)
 398 {
 399         struct inode *inode = dentry->d_inode;
 400         int error;
 401
 402         if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 403                 return -EPERM;
 404
 405         error = inode_change_ok(inode, attr);
 406         if (!error)
 407                 error = inode_setattr(inode, attr);
 408
 409         return error;
 410 }
 411
 412 /* I'm lazy and don't distinguish between files and directories,
 413  * until access time.
 414  */
 415 static const struct file_operations proc_sys_file_operations = {
 416         .read           = proc_sys_read,
 417         .write          = proc_sys_write,
 418         .readdir        = proc_sys_readdir,
 419 };
 420
 421 static const struct inode_operations proc_sys_inode_operations = {
 422         .lookup         = proc_sys_lookup,
 423         .permission     = proc_sys_permission,
 424         .setattr        = proc_sys_setattr,
 425 };
 426
 427 static int proc_sys_revalidate(struct dentry *dentry, struct nameidata *nd)
 428 {
 429         struct ctl_table_header *head;
 430         struct ctl_table *table;
 431         table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
 432         proc_sys_refresh_inode(dentry->d_inode, table);
 433         sysctl_head_finish(head);
 434         return !!table;
 435 }
 436
 437 static struct dentry_operations proc_sys_dentry_operations = {
 438         .d_revalidate   = proc_sys_revalidate,
 439 };
 440
 441 static struct proc_dir_entry *proc_sys_root;
 442
 443 int proc_sys_init(void)
 444 {
 445         proc_sys_root = proc_mkdir("sys", NULL);
 446         proc_sys_root->proc_iops = &proc_sys_inode_operations;
 447         proc_sys_root->proc_fops = &proc_sys_file_operations;
 448         proc_sys_root->nlink = 0;
 449         return 0;
 450 }