linux/fs/proc/proc_sysctl.c
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   1/*
   2 * /proc/sys support
   3 */
   4#include <linux/init.h>
   5#include <linux/sysctl.h>
   6#include <linux/proc_fs.h>
   7#include <linux/security.h>
   8#include <linux/namei.h>
   9#include "internal.h"
  10
  11static const struct dentry_operations proc_sys_dentry_operations;
  12static const struct file_operations proc_sys_file_operations;
  13static const struct inode_operations proc_sys_inode_operations;
  14static const struct file_operations proc_sys_dir_file_operations;
  15static const struct inode_operations proc_sys_dir_operations;
  16
  17static struct inode *proc_sys_make_inode(struct super_block *sb,
  18                struct ctl_table_header *head, struct ctl_table *table)
  19{
  20        struct inode *inode;
  21        struct proc_inode *ei;
  22
  23        inode = new_inode(sb);
  24        if (!inode)
  25                goto out;
  26
  27        inode->i_ino = get_next_ino();
  28
  29        sysctl_head_get(head);
  30        ei = PROC_I(inode);
  31        ei->sysctl = head;
  32        ei->sysctl_entry = table;
  33
  34        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
  35        inode->i_mode = table->mode;
  36        if (!table->child) {
  37                inode->i_mode |= S_IFREG;
  38                inode->i_op = &proc_sys_inode_operations;
  39                inode->i_fop = &proc_sys_file_operations;
  40        } else {
  41                inode->i_mode |= S_IFDIR;
  42                inode->i_nlink = 0;
  43                inode->i_op = &proc_sys_dir_operations;
  44                inode->i_fop = &proc_sys_dir_file_operations;
  45        }
  46out:
  47        return inode;
  48}
  49
  50static struct ctl_table *find_in_table(struct ctl_table *p, struct qstr *name)
  51{
  52        int len;
  53        for ( ; p->procname; p++) {
  54
  55                if (!p->procname)
  56                        continue;
  57
  58                len = strlen(p->procname);
  59                if (len != name->len)
  60                        continue;
  61
  62                if (memcmp(p->procname, name->name, len) != 0)
  63                        continue;
  64
  65                /* I have a match */
  66                return p;
  67        }
  68        return NULL;
  69}
  70
  71static struct ctl_table_header *grab_header(struct inode *inode)
  72{
  73        if (PROC_I(inode)->sysctl)
  74                return sysctl_head_grab(PROC_I(inode)->sysctl);
  75        else
  76                return sysctl_head_next(NULL);
  77}
  78
  79static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
  80                                        struct nameidata *nd)
  81{
  82        struct ctl_table_header *head = grab_header(dir);
  83        struct ctl_table *table = PROC_I(dir)->sysctl_entry;
  84        struct ctl_table_header *h = NULL;
  85        struct qstr *name = &dentry->d_name;
  86        struct ctl_table *p;
  87        struct inode *inode;
  88        struct dentry *err = ERR_PTR(-ENOENT);
  89
  90        if (IS_ERR(head))
  91                return ERR_CAST(head);
  92
  93        if (table && !table->child) {
  94                WARN_ON(1);
  95                goto out;
  96        }
  97
  98        table = table ? table->child : head->ctl_table;
  99
 100        p = find_in_table(table, name);
 101        if (!p) {
 102                for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
 103                        if (h->attached_to != table)
 104                                continue;
 105                        p = find_in_table(h->attached_by, name);
 106                        if (p)
 107                                break;
 108                }
 109        }
 110
 111        if (!p)
 112                goto out;
 113
 114        err = ERR_PTR(-ENOMEM);
 115        inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
 116        if (h)
 117                sysctl_head_finish(h);
 118
 119        if (!inode)
 120                goto out;
 121
 122        err = NULL;
 123        d_set_d_op(dentry, &proc_sys_dentry_operations);
 124        d_add(dentry, inode);
 125
 126out:
 127        sysctl_head_finish(head);
 128        return err;
 129}
 130
 131static ssize_t proc_sys_call_handler(struct file *filp, void __user *buf,
 132                size_t count, loff_t *ppos, int write)
 133{
 134        struct inode *inode = filp->f_path.dentry->d_inode;
 135        struct ctl_table_header *head = grab_header(inode);
 136        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
 137        ssize_t error;
 138        size_t res;
 139
 140        if (IS_ERR(head))
 141                return PTR_ERR(head);
 142
 143        /*
 144         * At this point we know that the sysctl was not unregistered
 145         * and won't be until we finish.
 146         */
 147        error = -EPERM;
 148        if (sysctl_perm(head->root, table, write ? MAY_WRITE : MAY_READ))
 149                goto out;
 150
 151        /* if that can happen at all, it should be -EINVAL, not -EISDIR */
 152        error = -EINVAL;
 153        if (!table->proc_handler)
 154                goto out;
 155
 156        /* careful: calling conventions are nasty here */
 157        res = count;
 158        error = table->proc_handler(table, write, buf, &res, ppos);
 159        if (!error)
 160                error = res;
 161out:
 162        sysctl_head_finish(head);
 163
 164        return error;
 165}
 166
 167static ssize_t proc_sys_read(struct file *filp, char __user *buf,
 168                                size_t count, loff_t *ppos)
 169{
 170        return proc_sys_call_handler(filp, (void __user *)buf, count, ppos, 0);
 171}
 172
 173static ssize_t proc_sys_write(struct file *filp, const char __user *buf,
 174                                size_t count, loff_t *ppos)
 175{
 176        return proc_sys_call_handler(filp, (void __user *)buf, count, ppos, 1);
 177}
 178
 179
 180static int proc_sys_fill_cache(struct file *filp, void *dirent,
 181                                filldir_t filldir,
 182                                struct ctl_table_header *head,
 183                                struct ctl_table *table)
 184{
 185        struct dentry *child, *dir = filp->f_path.dentry;
 186        struct inode *inode;
 187        struct qstr qname;
 188        ino_t ino = 0;
 189        unsigned type = DT_UNKNOWN;
 190
 191        qname.name = table->procname;
 192        qname.len  = strlen(table->procname);
 193        qname.hash = full_name_hash(qname.name, qname.len);
 194
 195        child = d_lookup(dir, &qname);
 196        if (!child) {
 197                child = d_alloc(dir, &qname);
 198                if (child) {
 199                        inode = proc_sys_make_inode(dir->d_sb, head, table);
 200                        if (!inode) {
 201                                dput(child);
 202                                return -ENOMEM;
 203                        } else {
 204                                d_set_d_op(child, &proc_sys_dentry_operations);
 205                                d_add(child, inode);
 206                        }
 207                } else {
 208                        return -ENOMEM;
 209                }
 210        }
 211        inode = child->d_inode;
 212        ino  = inode->i_ino;
 213        type = inode->i_mode >> 12;
 214        dput(child);
 215        return !!filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
 216}
 217
 218static int scan(struct ctl_table_header *head, ctl_table *table,
 219                unsigned long *pos, struct file *file,
 220                void *dirent, filldir_t filldir)
 221{
 222
 223        for (; table->procname; table++, (*pos)++) {
 224                int res;
 225
 226                /* Can't do anything without a proc name */
 227                if (!table->procname)
 228                        continue;
 229
 230                if (*pos < file->f_pos)
 231                        continue;
 232
 233                res = proc_sys_fill_cache(file, dirent, filldir, head, table);
 234                if (res)
 235                        return res;
 236
 237                file->f_pos = *pos + 1;
 238        }
 239        return 0;
 240}
 241
 242static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
 243{
 244        struct dentry *dentry = filp->f_path.dentry;
 245        struct inode *inode = dentry->d_inode;
 246        struct ctl_table_header *head = grab_header(inode);
 247        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
 248        struct ctl_table_header *h = NULL;
 249        unsigned long pos;
 250        int ret = -EINVAL;
 251
 252        if (IS_ERR(head))
 253                return PTR_ERR(head);
 254
 255        if (table && !table->child) {
 256                WARN_ON(1);
 257                goto out;
 258        }
 259
 260        table = table ? table->child : head->ctl_table;
 261
 262        ret = 0;
 263        /* Avoid a switch here: arm builds fail with missing __cmpdi2 */
 264        if (filp->f_pos == 0) {
 265                if (filldir(dirent, ".", 1, filp->f_pos,
 266                                inode->i_ino, DT_DIR) < 0)
 267                        goto out;
 268                filp->f_pos++;
 269        }
 270        if (filp->f_pos == 1) {
 271                if (filldir(dirent, "..", 2, filp->f_pos,
 272                                parent_ino(dentry), DT_DIR) < 0)
 273                        goto out;
 274                filp->f_pos++;
 275        }
 276        pos = 2;
 277
 278        ret = scan(head, table, &pos, filp, dirent, filldir);
 279        if (ret)
 280                goto out;
 281
 282        for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
 283                if (h->attached_to != table)
 284                        continue;
 285                ret = scan(h, h->attached_by, &pos, filp, dirent, filldir);
 286                if (ret) {
 287                        sysctl_head_finish(h);
 288                        break;
 289                }
 290        }
 291        ret = 1;
 292out:
 293        sysctl_head_finish(head);
 294        return ret;
 295}
 296
 297static int proc_sys_permission(struct inode *inode, int mask,unsigned int flags)
 298{
 299        /*
 300         * sysctl entries that are not writeable,
 301         * are _NOT_ writeable, capabilities or not.
 302         */
 303        struct ctl_table_header *head;
 304        struct ctl_table *table;
 305        int error;
 306
 307        if (flags & IPERM_FLAG_RCU)
 308                return -ECHILD;
 309
 310        /* Executable files are not allowed under /proc/sys/ */
 311        if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode))
 312                return -EACCES;
 313
 314        head = grab_header(inode);
 315        if (IS_ERR(head))
 316                return PTR_ERR(head);
 317
 318        table = PROC_I(inode)->sysctl_entry;
 319        if (!table) /* global root - r-xr-xr-x */
 320                error = mask & MAY_WRITE ? -EACCES : 0;
 321        else /* Use the permissions on the sysctl table entry */
 322                error = sysctl_perm(head->root, table, mask);
 323
 324        sysctl_head_finish(head);
 325        return error;
 326}
 327
 328static int proc_sys_setattr(struct dentry *dentry, struct iattr *attr)
 329{
 330        struct inode *inode = dentry->d_inode;
 331        int error;
 332
 333        if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
 334                return -EPERM;
 335
 336        error = inode_change_ok(inode, attr);
 337        if (error)
 338                return error;
 339
 340        if ((attr->ia_valid & ATTR_SIZE) &&
 341            attr->ia_size != i_size_read(inode)) {
 342                error = vmtruncate(inode, attr->ia_size);
 343                if (error)
 344                        return error;
 345        }
 346
 347        setattr_copy(inode, attr);
 348        mark_inode_dirty(inode);
 349        return 0;
 350}
 351
 352static int proc_sys_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
 353{
 354        struct inode *inode = dentry->d_inode;
 355        struct ctl_table_header *head = grab_header(inode);
 356        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
 357
 358        if (IS_ERR(head))
 359                return PTR_ERR(head);
 360
 361        generic_fillattr(inode, stat);
 362        if (table)
 363                stat->mode = (stat->mode & S_IFMT) | table->mode;
 364
 365        sysctl_head_finish(head);
 366        return 0;
 367}
 368
 369static const struct file_operations proc_sys_file_operations = {
 370        .read           = proc_sys_read,
 371        .write          = proc_sys_write,
 372        .llseek         = default_llseek,
 373};
 374
 375static const struct file_operations proc_sys_dir_file_operations = {
 376        .readdir        = proc_sys_readdir,
 377        .llseek         = generic_file_llseek,
 378};
 379
 380static const struct inode_operations proc_sys_inode_operations = {
 381        .permission     = proc_sys_permission,
 382        .setattr        = proc_sys_setattr,
 383        .getattr        = proc_sys_getattr,
 384};
 385
 386static const struct inode_operations proc_sys_dir_operations = {
 387        .lookup         = proc_sys_lookup,
 388        .permission     = proc_sys_permission,
 389        .setattr        = proc_sys_setattr,
 390        .getattr        = proc_sys_getattr,
 391};
 392
 393static int proc_sys_revalidate(struct dentry *dentry, struct nameidata *nd)
 394{
 395        if (nd->flags & LOOKUP_RCU)
 396                return -ECHILD;
 397        return !PROC_I(dentry->d_inode)->sysctl->unregistering;
 398}
 399
 400static int proc_sys_delete(const struct dentry *dentry)
 401{
 402        return !!PROC_I(dentry->d_inode)->sysctl->unregistering;
 403}
 404
 405static int proc_sys_compare(const struct dentry *parent,
 406                const struct inode *pinode,
 407                const struct dentry *dentry, const struct inode *inode,
 408                unsigned int len, const char *str, const struct qstr *name)
 409{
 410        struct ctl_table_header *head;
 411        /* Although proc doesn't have negative dentries, rcu-walk means
 412         * that inode here can be NULL */
 413        /* AV: can it, indeed? */
 414        if (!inode)
 415                return 1;
 416        if (name->len != len)
 417                return 1;
 418        if (memcmp(name->name, str, len))
 419                return 1;
 420        head = rcu_dereference(PROC_I(inode)->sysctl);
 421        return !head || !sysctl_is_seen(head);
 422}
 423
 424static const struct dentry_operations proc_sys_dentry_operations = {
 425        .d_revalidate   = proc_sys_revalidate,
 426        .d_delete       = proc_sys_delete,
 427        .d_compare      = proc_sys_compare,
 428};
 429
 430int __init proc_sys_init(void)
 431{
 432        struct proc_dir_entry *proc_sys_root;
 433
 434        proc_sys_root = proc_mkdir("sys", NULL);
 435        proc_sys_root->proc_iops = &proc_sys_dir_operations;
 436        proc_sys_root->proc_fops = &proc_sys_dir_file_operations;
 437        proc_sys_root->nlink = 0;
 438        return 0;
 439}
 440