fs/attr.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/fs/attr.c
   4  *
   5  *  Copyright (C) 1991, 1992  Linus Torvalds
   6  *  changes by Thomas Schoebel-Theuer
   7  */
   8
   9 #include <linux/export.h>
  10 #include <linux/time.h>
  11 #include <linux/mm.h>
  12 #include <linux/string.h>
  13 #include <linux/sched/signal.h>
  14 #include <linux/capability.h>
  15 #include <linux/fsnotify.h>
  16 #include <linux/fcntl.h>
  17 #include <linux/filelock.h>
  18 #include <linux/security.h>
  19 #include <linux/evm.h>
  20 #include <linux/ima.h>
  21
  22 #include "internal.h"
  23
  24 /**
  25  * setattr_should_drop_sgid - determine whether the setgid bit needs to be
  26  *                            removed
  27  * @idmap:      idmap of the mount @inode was found from
  28  * @inode:      inode to check
  29  *
  30  * This function determines whether the setgid bit needs to be removed.
  31  * We retain backwards compatibility and require setgid bit to be removed
  32  * unconditionally if S_IXGRP is set. Otherwise we have the exact same
  33  * requirements as setattr_prepare() and setattr_copy().
  34  *
  35  * Return: ATTR_KILL_SGID if setgid bit needs to be removed, 0 otherwise.
  36  */
  37 int setattr_should_drop_sgid(struct mnt_idmap *idmap,
  38                              const struct inode *inode)
  39 {
  40         umode_t mode = inode->i_mode;
  41
  42         if (!(mode & S_ISGID))
  43                 return 0;
  44         if (mode & S_IXGRP)
  45                 return ATTR_KILL_SGID;
  46         if (!in_group_or_capable(idmap, inode, i_gid_into_vfsgid(idmap, inode)))
  47                 return ATTR_KILL_SGID;
  48         return 0;
  49 }
  50
  51 /**
  52  * setattr_should_drop_suidgid - determine whether the set{g,u}id bit needs to
  53  *                               be dropped
  54  * @idmap:      idmap of the mount @inode was found from
  55  * @inode:      inode to check
  56  *
  57  * This function determines whether the set{g,u}id bits need to be removed.
  58  * If the setuid bit needs to be removed ATTR_KILL_SUID is returned. If the
  59  * setgid bit needs to be removed ATTR_KILL_SGID is returned. If both
  60  * set{g,u}id bits need to be removed the corresponding mask of both flags is
  61  * returned.
  62  *
  63  * Return: A mask of ATTR_KILL_S{G,U}ID indicating which - if any - setid bits
  64  * to remove, 0 otherwise.
  65  */
  66 int setattr_should_drop_suidgid(struct mnt_idmap *idmap,
  67                                 struct inode *inode)
  68 {
  69         umode_t mode = inode->i_mode;
  70         int kill = 0;
  71
  72         /* suid always must be killed */
  73         if (unlikely(mode & S_ISUID))
  74                 kill = ATTR_KILL_SUID;
  75
  76         kill |= setattr_should_drop_sgid(idmap, inode);
  77
  78         if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
  79                 return kill;
  80
  81         return 0;
  82 }
  83 EXPORT_SYMBOL(setattr_should_drop_suidgid);
  84
  85 /**
  86  * chown_ok - verify permissions to chown inode
  87  * @idmap:      idmap of the mount @inode was found from
  88  * @inode:      inode to check permissions on
  89  * @ia_vfsuid:  uid to chown @inode to
  90  *
  91  * If the inode has been found through an idmapped mount the idmap of
  92  * the vfsmount must be passed through @idmap. This function will then
  93  * take care to map the inode according to @idmap before checking
  94  * permissions. On non-idmapped mounts or if permission checking is to be
  95  * performed on the raw inode simply pass @nop_mnt_idmap.
  96  */
  97 static bool chown_ok(struct mnt_idmap *idmap,
  98                      const struct inode *inode, vfsuid_t ia_vfsuid)
  99 {
 100         vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode);
 101         if (vfsuid_eq_kuid(vfsuid, current_fsuid()) &&
 102             vfsuid_eq(ia_vfsuid, vfsuid))
 103                 return true;
 104         if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN))
 105                 return true;
 106         if (!vfsuid_valid(vfsuid) &&
 107             ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
 108                 return true;
 109         return false;
 110 }
 111
 112 /**
 113  * chgrp_ok - verify permissions to chgrp inode
 114  * @idmap:      idmap of the mount @inode was found from
 115  * @inode:      inode to check permissions on
 116  * @ia_vfsgid:  gid to chown @inode to
 117  *
 118  * If the inode has been found through an idmapped mount the idmap of
 119  * the vfsmount must be passed through @idmap. This function will then
 120  * take care to map the inode according to @idmap before checking
 121  * permissions. On non-idmapped mounts or if permission checking is to be
 122  * performed on the raw inode simply pass @nop_mnt_idmap.
 123  */
 124 static bool chgrp_ok(struct mnt_idmap *idmap,
 125                      const struct inode *inode, vfsgid_t ia_vfsgid)
 126 {
 127         vfsgid_t vfsgid = i_gid_into_vfsgid(idmap, inode);
 128         vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode);
 129         if (vfsuid_eq_kuid(vfsuid, current_fsuid())) {
 130                 if (vfsgid_eq(ia_vfsgid, vfsgid))
 131                         return true;
 132                 if (vfsgid_in_group_p(ia_vfsgid))
 133                         return true;
 134         }
 135         if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN))
 136                 return true;
 137         if (!vfsgid_valid(vfsgid) &&
 138             ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
 139                 return true;
 140         return false;
 141 }
 142
 143 /**
 144  * setattr_prepare - check if attribute changes to a dentry are allowed
 145  * @idmap:      idmap of the mount the inode was found from
 146  * @dentry:     dentry to check
 147  * @attr:       attributes to change
 148  *
 149  * Check if we are allowed to change the attributes contained in @attr
 150  * in the given dentry.  This includes the normal unix access permission
 151  * checks, as well as checks for rlimits and others. The function also clears
 152  * SGID bit from mode if user is not allowed to set it. Also file capabilities
 153  * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
 154  *
 155  * If the inode has been found through an idmapped mount the idmap of
 156  * the vfsmount must be passed through @idmap. This function will then
 157  * take care to map the inode according to @idmap before checking
 158  * permissions. On non-idmapped mounts or if permission checking is to be
 159  * performed on the raw inode simply passs @nop_mnt_idmap.
 160  *
 161  * Should be called as the first thing in ->setattr implementations,
 162  * possibly after taking additional locks.
 163  */
 164 int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry,
 165                     struct iattr *attr)
 166 {
 167         struct inode *inode = d_inode(dentry);
 168         unsigned int ia_valid = attr->ia_valid;
 169
 170         /*
 171          * First check size constraints.  These can't be overriden using
 172          * ATTR_FORCE.
 173          */
 174         if (ia_valid & ATTR_SIZE) {
 175                 int error = inode_newsize_ok(inode, attr->ia_size);
 176                 if (error)
 177                         return error;
 178         }
 179
 180         /* If force is set do it anyway. */
 181         if (ia_valid & ATTR_FORCE)
 182                 goto kill_priv;
 183
 184         /* Make sure a caller can chown. */
 185         if ((ia_valid & ATTR_UID) &&
 186             !chown_ok(idmap, inode, attr->ia_vfsuid))
 187                 return -EPERM;
 188
 189         /* Make sure caller can chgrp. */
 190         if ((ia_valid & ATTR_GID) &&
 191             !chgrp_ok(idmap, inode, attr->ia_vfsgid))
 192                 return -EPERM;
 193
 194         /* Make sure a caller can chmod. */
 195         if (ia_valid & ATTR_MODE) {
 196                 vfsgid_t vfsgid;
 197
 198                 if (!inode_owner_or_capable(idmap, inode))
 199                         return -EPERM;
 200
 201                 if (ia_valid & ATTR_GID)
 202                         vfsgid = attr->ia_vfsgid;
 203                 else
 204                         vfsgid = i_gid_into_vfsgid(idmap, inode);
 205
 206                 /* Also check the setgid bit! */
 207                 if (!in_group_or_capable(idmap, inode, vfsgid))
 208                         attr->ia_mode &= ~S_ISGID;
 209         }
 210
 211         /* Check for setting the inode time. */
 212         if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
 213                 if (!inode_owner_or_capable(idmap, inode))
 214                         return -EPERM;
 215         }
 216
 217 kill_priv:
 218         /* User has permission for the change */
 219         if (ia_valid & ATTR_KILL_PRIV) {
 220                 int error;
 221
 222                 error = security_inode_killpriv(idmap, dentry);
 223                 if (error)
 224                         return error;
 225         }
 226
 227         return 0;
 228 }
 229 EXPORT_SYMBOL(setattr_prepare);
 230
 231 /**
 232  * inode_newsize_ok - may this inode be truncated to a given size
 233  * @inode:      the inode to be truncated
 234  * @offset:     the new size to assign to the inode
 235  *
 236  * inode_newsize_ok must be called with i_mutex held.
 237  *
 238  * inode_newsize_ok will check filesystem limits and ulimits to check that the
 239  * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
 240  * when necessary. Caller must not proceed with inode size change if failure is
 241  * returned. @inode must be a file (not directory), with appropriate
 242  * permissions to allow truncate (inode_newsize_ok does NOT check these
 243  * conditions).
 244  *
 245  * Return: 0 on success, -ve errno on failure
 246  */
 247 int inode_newsize_ok(const struct inode *inode, loff_t offset)
 248 {
 249         if (offset < 0)
 250                 return -EINVAL;
 251         if (inode->i_size < offset) {
 252                 unsigned long limit;
 253
 254                 limit = rlimit(RLIMIT_FSIZE);
 255                 if (limit != RLIM_INFINITY && offset > limit)
 256                         goto out_sig;
 257                 if (offset > inode->i_sb->s_maxbytes)
 258                         goto out_big;
 259         } else {
 260                 /*
 261                  * truncation of in-use swapfiles is disallowed - it would
 262                  * cause subsequent swapout to scribble on the now-freed
 263                  * blocks.
 264                  */
 265                 if (IS_SWAPFILE(inode))
 266                         return -ETXTBSY;
 267         }
 268
 269         return 0;
 270 out_sig:
 271         send_sig(SIGXFSZ, current, 0);
 272 out_big:
 273         return -EFBIG;
 274 }
 275 EXPORT_SYMBOL(inode_newsize_ok);
 276
 277 /**
 278  * setattr_copy - copy simple metadata updates into the generic inode
 279  * @idmap:      idmap of the mount the inode was found from
 280  * @inode:      the inode to be updated
 281  * @attr:       the new attributes
 282  *
 283  * setattr_copy must be called with i_mutex held.
 284  *
 285  * setattr_copy updates the inode's metadata with that specified
 286  * in attr on idmapped mounts. Necessary permission checks to determine
 287  * whether or not the S_ISGID property needs to be removed are performed with
 288  * the correct idmapped mount permission helpers.
 289  * Noticeably missing is inode size update, which is more complex
 290  * as it requires pagecache updates.
 291  *
 292  * If the inode has been found through an idmapped mount the idmap of
 293  * the vfsmount must be passed through @idmap. This function will then
 294  * take care to map the inode according to @idmap before checking
 295  * permissions. On non-idmapped mounts or if permission checking is to be
 296  * performed on the raw inode simply pass @nop_mnt_idmap.
 297  *
 298  * The inode is not marked as dirty after this operation. The rationale is
 299  * that for "simple" filesystems, the struct inode is the inode storage.
 300  * The caller is free to mark the inode dirty afterwards if needed.
 301  */
 302 void setattr_copy(struct mnt_idmap *idmap, struct inode *inode,
 303                   const struct iattr *attr)
 304 {
 305         unsigned int ia_valid = attr->ia_valid;
 306
 307         i_uid_update(idmap, attr, inode);
 308         i_gid_update(idmap, attr, inode);
 309         if (ia_valid & ATTR_ATIME)
 310                 inode->i_atime = attr->ia_atime;
 311         if (ia_valid & ATTR_MTIME)
 312                 inode->i_mtime = attr->ia_mtime;
 313         if (ia_valid & ATTR_CTIME)
 314                 inode->i_ctime = attr->ia_ctime;
 315         if (ia_valid & ATTR_MODE) {
 316                 umode_t mode = attr->ia_mode;
 317                 if (!in_group_or_capable(idmap, inode,
 318                                          i_gid_into_vfsgid(idmap, inode)))
 319                         mode &= ~S_ISGID;
 320                 inode->i_mode = mode;
 321         }
 322 }
 323 EXPORT_SYMBOL(setattr_copy);
 324
 325 int may_setattr(struct mnt_idmap *idmap, struct inode *inode,
 326                 unsigned int ia_valid)
 327 {
 328         int error;
 329
 330         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
 331                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 332                         return -EPERM;
 333         }
 334
 335         /*
 336          * If utimes(2) and friends are called with times == NULL (or both
 337          * times are UTIME_NOW), then we need to check for write permission
 338          */
 339         if (ia_valid & ATTR_TOUCH) {
 340                 if (IS_IMMUTABLE(inode))
 341                         return -EPERM;
 342
 343                 if (!inode_owner_or_capable(idmap, inode)) {
 344                         error = inode_permission(idmap, inode, MAY_WRITE);
 345                         if (error)
 346                                 return error;
 347                 }
 348         }
 349         return 0;
 350 }
 351 EXPORT_SYMBOL(may_setattr);
 352
 353 /**
 354  * notify_change - modify attributes of a filesytem object
 355  * @idmap:      idmap of the mount the inode was found from
 356  * @dentry:     object affected
 357  * @attr:       new attributes
 358  * @delegated_inode: returns inode, if the inode is delegated
 359  *
 360  * The caller must hold the i_mutex on the affected object.
 361  *
 362  * If notify_change discovers a delegation in need of breaking,
 363  * it will return -EWOULDBLOCK and return a reference to the inode in
 364  * delegated_inode.  The caller should then break the delegation and
 365  * retry.  Because breaking a delegation may take a long time, the
 366  * caller should drop the i_mutex before doing so.
 367  *
 368  * Alternatively, a caller may pass NULL for delegated_inode.  This may
 369  * be appropriate for callers that expect the underlying filesystem not
 370  * to be NFS exported.  Also, passing NULL is fine for callers holding
 371  * the file open for write, as there can be no conflicting delegation in
 372  * that case.
 373  *
 374  * If the inode has been found through an idmapped mount the idmap of
 375  * the vfsmount must be passed through @idmap. This function will then
 376  * take care to map the inode according to @idmap before checking
 377  * permissions. On non-idmapped mounts or if permission checking is to be
 378  * performed on the raw inode simply pass @nop_mnt_idmap.
 379  */
 380 int notify_change(struct mnt_idmap *idmap, struct dentry *dentry,
 381                   struct iattr *attr, struct inode **delegated_inode)
 382 {
 383         struct inode *inode = dentry->d_inode;
 384         umode_t mode = inode->i_mode;
 385         int error;
 386         struct timespec64 now;
 387         unsigned int ia_valid = attr->ia_valid;
 388
 389         WARN_ON_ONCE(!inode_is_locked(inode));
 390
 391         error = may_setattr(idmap, inode, ia_valid);
 392         if (error)
 393                 return error;
 394
 395         if ((ia_valid & ATTR_MODE)) {
 396                 umode_t amode = attr->ia_mode;
 397                 /* Flag setting protected by i_mutex */
 398                 if (is_sxid(amode))
 399                         inode->i_flags &= ~S_NOSEC;
 400         }
 401
 402         now = current_time(inode);
 403
 404         attr->ia_ctime = now;
 405         if (!(ia_valid & ATTR_ATIME_SET))
 406                 attr->ia_atime = now;
 407         else
 408                 attr->ia_atime = timestamp_truncate(attr->ia_atime, inode);
 409         if (!(ia_valid & ATTR_MTIME_SET))
 410                 attr->ia_mtime = now;
 411         else
 412                 attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode);
 413
 414         if (ia_valid & ATTR_KILL_PRIV) {
 415                 error = security_inode_need_killpriv(dentry);
 416                 if (error < 0)
 417                         return error;
 418                 if (error == 0)
 419                         ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
 420         }
 421
 422         /*
 423          * We now pass ATTR_KILL_S*ID to the lower level setattr function so
 424          * that the function has the ability to reinterpret a mode change
 425          * that's due to these bits. This adds an implicit restriction that
 426          * no function will ever call notify_change with both ATTR_MODE and
 427          * ATTR_KILL_S*ID set.
 428          */
 429         if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
 430             (ia_valid & ATTR_MODE))
 431                 BUG();
 432
 433         if (ia_valid & ATTR_KILL_SUID) {
 434                 if (mode & S_ISUID) {
 435                         ia_valid = attr->ia_valid |= ATTR_MODE;
 436                         attr->ia_mode = (inode->i_mode & ~S_ISUID);
 437                 }
 438         }
 439         if (ia_valid & ATTR_KILL_SGID) {
 440                 if (mode & S_ISGID) {
 441                         if (!(ia_valid & ATTR_MODE)) {
 442                                 ia_valid = attr->ia_valid |= ATTR_MODE;
 443                                 attr->ia_mode = inode->i_mode;
 444                         }
 445                         attr->ia_mode &= ~S_ISGID;
 446                 }
 447         }
 448         if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
 449                 return 0;
 450
 451         /*
 452          * Verify that uid/gid changes are valid in the target
 453          * namespace of the superblock.
 454          */
 455         if (ia_valid & ATTR_UID &&
 456             !vfsuid_has_fsmapping(idmap, inode->i_sb->s_user_ns,
 457                                   attr->ia_vfsuid))
 458                 return -EOVERFLOW;
 459         if (ia_valid & ATTR_GID &&
 460             !vfsgid_has_fsmapping(idmap, inode->i_sb->s_user_ns,
 461                                   attr->ia_vfsgid))
 462                 return -EOVERFLOW;
 463
 464         /* Don't allow modifications of files with invalid uids or
 465          * gids unless those uids & gids are being made valid.
 466          */
 467         if (!(ia_valid & ATTR_UID) &&
 468             !vfsuid_valid(i_uid_into_vfsuid(idmap, inode)))
 469                 return -EOVERFLOW;
 470         if (!(ia_valid & ATTR_GID) &&
 471             !vfsgid_valid(i_gid_into_vfsgid(idmap, inode)))
 472                 return -EOVERFLOW;
 473
 474         error = security_inode_setattr(idmap, dentry, attr);
 475         if (error)
 476                 return error;
 477         error = try_break_deleg(inode, delegated_inode);
 478         if (error)
 479                 return error;
 480
 481         if (inode->i_op->setattr)
 482                 error = inode->i_op->setattr(idmap, dentry, attr);
 483         else
 484                 error = simple_setattr(idmap, dentry, attr);
 485
 486         if (!error) {
 487                 fsnotify_change(dentry, ia_valid);
 488                 ima_inode_post_setattr(idmap, dentry);
 489                 evm_inode_post_setattr(dentry, ia_valid);
 490         }
 491
 492         return error;
 493 }
 494 EXPORT_SYMBOL(notify_change);