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/security.h>
  18 #include <linux/evm.h>
  19 #include <linux/ima.h>
  20
  21 /**
  22  * chown_ok - verify permissions to chown inode
  23  * @mnt_userns: user namespace of the mount @inode was found from
  24  * @inode:      inode to check permissions on
  25  * @uid:        uid to chown @inode to
  26  *
  27  * If the inode has been found through an idmapped mount the user namespace of
  28  * the vfsmount must be passed through @mnt_userns. This function will then
  29  * take care to map the inode according to @mnt_userns before checking
  30  * permissions. On non-idmapped mounts or if permission checking is to be
  31  * performed on the raw inode simply passs init_user_ns.
  32  */
  33 static bool chown_ok(struct user_namespace *mnt_userns,
  34                      const struct inode *inode,
  35                      kuid_t uid)
  36 {
  37         kuid_t kuid = i_uid_into_mnt(mnt_userns, inode);
  38         if (uid_eq(current_fsuid(), kuid) && uid_eq(uid, inode->i_uid))
  39                 return true;
  40         if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_CHOWN))
  41                 return true;
  42         if (uid_eq(kuid, INVALID_UID) &&
  43             ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  44                 return true;
  45         return false;
  46 }
  47
  48 /**
  49  * chgrp_ok - verify permissions to chgrp inode
  50  * @mnt_userns: user namespace of the mount @inode was found from
  51  * @inode:      inode to check permissions on
  52  * @gid:        gid to chown @inode to
  53  *
  54  * If the inode has been found through an idmapped mount the user namespace of
  55  * the vfsmount must be passed through @mnt_userns. This function will then
  56  * take care to map the inode according to @mnt_userns before checking
  57  * permissions. On non-idmapped mounts or if permission checking is to be
  58  * performed on the raw inode simply passs init_user_ns.
  59  */
  60 static bool chgrp_ok(struct user_namespace *mnt_userns,
  61                      const struct inode *inode, kgid_t gid)
  62 {
  63         kgid_t kgid = i_gid_into_mnt(mnt_userns, inode);
  64         if (uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) &&
  65             (in_group_p(gid) || gid_eq(gid, inode->i_gid)))
  66                 return true;
  67         if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_CHOWN))
  68                 return true;
  69         if (gid_eq(kgid, INVALID_GID) &&
  70             ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  71                 return true;
  72         return false;
  73 }
  74
  75 /**
  76  * setattr_prepare - check if attribute changes to a dentry are allowed
  77  * @mnt_userns: user namespace of the mount the inode was found from
  78  * @dentry:     dentry to check
  79  * @attr:       attributes to change
  80  *
  81  * Check if we are allowed to change the attributes contained in @attr
  82  * in the given dentry.  This includes the normal unix access permission
  83  * checks, as well as checks for rlimits and others. The function also clears
  84  * SGID bit from mode if user is not allowed to set it. Also file capabilities
  85  * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
  86  *
  87  * If the inode has been found through an idmapped mount the user namespace of
  88  * the vfsmount must be passed through @mnt_userns. This function will then
  89  * take care to map the inode according to @mnt_userns before checking
  90  * permissions. On non-idmapped mounts or if permission checking is to be
  91  * performed on the raw inode simply passs init_user_ns.
  92  *
  93  * Should be called as the first thing in ->setattr implementations,
  94  * possibly after taking additional locks.
  95  */
  96 int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry,
  97                     struct iattr *attr)
  98 {
  99         struct inode *inode = d_inode(dentry);
 100         unsigned int ia_valid = attr->ia_valid;
 101
 102         /*
 103          * First check size constraints.  These can't be overriden using
 104          * ATTR_FORCE.
 105          */
 106         if (ia_valid & ATTR_SIZE) {
 107                 int error = inode_newsize_ok(inode, attr->ia_size);
 108                 if (error)
 109                         return error;
 110         }
 111
 112         /* If force is set do it anyway. */
 113         if (ia_valid & ATTR_FORCE)
 114                 goto kill_priv;
 115
 116         /* Make sure a caller can chown. */
 117         if ((ia_valid & ATTR_UID) && !chown_ok(mnt_userns, inode, attr->ia_uid))
 118                 return -EPERM;
 119
 120         /* Make sure caller can chgrp. */
 121         if ((ia_valid & ATTR_GID) && !chgrp_ok(mnt_userns, inode, attr->ia_gid))
 122                 return -EPERM;
 123
 124         /* Make sure a caller can chmod. */
 125         if (ia_valid & ATTR_MODE) {
 126                 if (!inode_owner_or_capable(mnt_userns, inode))
 127                         return -EPERM;
 128                 /* Also check the setgid bit! */
 129                if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
 130                                 i_gid_into_mnt(mnt_userns, inode)) &&
 131                     !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
 132                         attr->ia_mode &= ~S_ISGID;
 133         }
 134
 135         /* Check for setting the inode time. */
 136         if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
 137                 if (!inode_owner_or_capable(mnt_userns, inode))
 138                         return -EPERM;
 139         }
 140
 141 kill_priv:
 142         /* User has permission for the change */
 143         if (ia_valid & ATTR_KILL_PRIV) {
 144                 int error;
 145
 146                 error = security_inode_killpriv(mnt_userns, dentry);
 147                 if (error)
 148                         return error;
 149         }
 150
 151         return 0;
 152 }
 153 EXPORT_SYMBOL(setattr_prepare);
 154
 155 /**
 156  * inode_newsize_ok - may this inode be truncated to a given size
 157  * @inode:      the inode to be truncated
 158  * @offset:     the new size to assign to the inode
 159  *
 160  * inode_newsize_ok must be called with i_mutex held.
 161  *
 162  * inode_newsize_ok will check filesystem limits and ulimits to check that the
 163  * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
 164  * when necessary. Caller must not proceed with inode size change if failure is
 165  * returned. @inode must be a file (not directory), with appropriate
 166  * permissions to allow truncate (inode_newsize_ok does NOT check these
 167  * conditions).
 168  *
 169  * Return: 0 on success, -ve errno on failure
 170  */
 171 int inode_newsize_ok(const struct inode *inode, loff_t offset)
 172 {
 173         if (inode->i_size < offset) {
 174                 unsigned long limit;
 175
 176                 limit = rlimit(RLIMIT_FSIZE);
 177                 if (limit != RLIM_INFINITY && offset > limit)
 178                         goto out_sig;
 179                 if (offset > inode->i_sb->s_maxbytes)
 180                         goto out_big;
 181         } else {
 182                 /*
 183                  * truncation of in-use swapfiles is disallowed - it would
 184                  * cause subsequent swapout to scribble on the now-freed
 185                  * blocks.
 186                  */
 187                 if (IS_SWAPFILE(inode))
 188                         return -ETXTBSY;
 189         }
 190
 191         return 0;
 192 out_sig:
 193         send_sig(SIGXFSZ, current, 0);
 194 out_big:
 195         return -EFBIG;
 196 }
 197 EXPORT_SYMBOL(inode_newsize_ok);
 198
 199 /**
 200  * setattr_copy - copy simple metadata updates into the generic inode
 201  * @mnt_userns: user namespace of the mount the inode was found from
 202  * @inode:      the inode to be updated
 203  * @attr:       the new attributes
 204  *
 205  * setattr_copy must be called with i_mutex held.
 206  *
 207  * setattr_copy updates the inode's metadata with that specified
 208  * in attr on idmapped mounts. If file ownership is changed setattr_copy
 209  * doesn't map ia_uid and ia_gid. It will asssume the caller has already
 210  * provided the intended values. Necessary permission checks to determine
 211  * whether or not the S_ISGID property needs to be removed are performed with
 212  * the correct idmapped mount permission helpers.
 213  * Noticeably missing is inode size update, which is more complex
 214  * as it requires pagecache updates.
 215  *
 216  * If the inode has been found through an idmapped mount the user namespace of
 217  * the vfsmount must be passed through @mnt_userns. This function will then
 218  * take care to map the inode according to @mnt_userns before checking
 219  * permissions. On non-idmapped mounts or if permission checking is to be
 220  * performed on the raw inode simply passs init_user_ns.
 221  *
 222  * The inode is not marked as dirty after this operation. The rationale is
 223  * that for "simple" filesystems, the struct inode is the inode storage.
 224  * The caller is free to mark the inode dirty afterwards if needed.
 225  */
 226 void setattr_copy(struct user_namespace *mnt_userns, struct inode *inode,
 227                   const struct iattr *attr)
 228 {
 229         unsigned int ia_valid = attr->ia_valid;
 230
 231         if (ia_valid & ATTR_UID)
 232                 inode->i_uid = attr->ia_uid;
 233         if (ia_valid & ATTR_GID)
 234                 inode->i_gid = attr->ia_gid;
 235         if (ia_valid & ATTR_ATIME)
 236                 inode->i_atime = attr->ia_atime;
 237         if (ia_valid & ATTR_MTIME)
 238                 inode->i_mtime = attr->ia_mtime;
 239         if (ia_valid & ATTR_CTIME)
 240                 inode->i_ctime = attr->ia_ctime;
 241         if (ia_valid & ATTR_MODE) {
 242                 umode_t mode = attr->ia_mode;
 243                 kgid_t kgid = i_gid_into_mnt(mnt_userns, inode);
 244                 if (!in_group_p(kgid) &&
 245                     !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
 246                         mode &= ~S_ISGID;
 247                 inode->i_mode = mode;
 248         }
 249 }
 250 EXPORT_SYMBOL(setattr_copy);
 251
 252 int may_setattr(struct user_namespace *mnt_userns, struct inode *inode,
 253                 unsigned int ia_valid)
 254 {
 255         int error;
 256
 257         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
 258                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 259                         return -EPERM;
 260         }
 261
 262         /*
 263          * If utimes(2) and friends are called with times == NULL (or both
 264          * times are UTIME_NOW), then we need to check for write permission
 265          */
 266         if (ia_valid & ATTR_TOUCH) {
 267                 if (IS_IMMUTABLE(inode))
 268                         return -EPERM;
 269
 270                 if (!inode_owner_or_capable(mnt_userns, inode)) {
 271                         error = inode_permission(mnt_userns, inode, MAY_WRITE);
 272                         if (error)
 273                                 return error;
 274                 }
 275         }
 276         return 0;
 277 }
 278 EXPORT_SYMBOL(may_setattr);
 279
 280 /**
 281  * notify_change - modify attributes of a filesytem object
 282  * @mnt_userns: user namespace of the mount the inode was found from
 283  * @dentry:     object affected
 284  * @attr:       new attributes
 285  * @delegated_inode: returns inode, if the inode is delegated
 286  *
 287  * The caller must hold the i_mutex on the affected object.
 288  *
 289  * If notify_change discovers a delegation in need of breaking,
 290  * it will return -EWOULDBLOCK and return a reference to the inode in
 291  * delegated_inode.  The caller should then break the delegation and
 292  * retry.  Because breaking a delegation may take a long time, the
 293  * caller should drop the i_mutex before doing so.
 294  *
 295  * If file ownership is changed notify_change() doesn't map ia_uid and
 296  * ia_gid. It will asssume the caller has already provided the intended values.
 297  *
 298  * Alternatively, a caller may pass NULL for delegated_inode.  This may
 299  * be appropriate for callers that expect the underlying filesystem not
 300  * to be NFS exported.  Also, passing NULL is fine for callers holding
 301  * the file open for write, as there can be no conflicting delegation in
 302  * that case.
 303  *
 304  * If the inode has been found through an idmapped mount the user namespace of
 305  * the vfsmount must be passed through @mnt_userns. This function will then
 306  * take care to map the inode according to @mnt_userns before checking
 307  * permissions. On non-idmapped mounts or if permission checking is to be
 308  * performed on the raw inode simply passs init_user_ns.
 309  */
 310 int notify_change(struct user_namespace *mnt_userns, struct dentry *dentry,
 311                   struct iattr *attr, struct inode **delegated_inode)
 312 {
 313         struct inode *inode = dentry->d_inode;
 314         umode_t mode = inode->i_mode;
 315         int error;
 316         struct timespec64 now;
 317         unsigned int ia_valid = attr->ia_valid;
 318
 319         WARN_ON_ONCE(!inode_is_locked(inode));
 320
 321         error = may_setattr(mnt_userns, inode, ia_valid);
 322         if (error)
 323                 return error;
 324
 325         if ((ia_valid & ATTR_MODE)) {
 326                 umode_t amode = attr->ia_mode;
 327                 /* Flag setting protected by i_mutex */
 328                 if (is_sxid(amode))
 329                         inode->i_flags &= ~S_NOSEC;
 330         }
 331
 332         now = current_time(inode);
 333
 334         attr->ia_ctime = now;
 335         if (!(ia_valid & ATTR_ATIME_SET))
 336                 attr->ia_atime = now;
 337         else
 338                 attr->ia_atime = timestamp_truncate(attr->ia_atime, inode);
 339         if (!(ia_valid & ATTR_MTIME_SET))
 340                 attr->ia_mtime = now;
 341         else
 342                 attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode);
 343
 344         if (ia_valid & ATTR_KILL_PRIV) {
 345                 error = security_inode_need_killpriv(dentry);
 346                 if (error < 0)
 347                         return error;
 348                 if (error == 0)
 349                         ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
 350         }
 351
 352         /*
 353          * We now pass ATTR_KILL_S*ID to the lower level setattr function so
 354          * that the function has the ability to reinterpret a mode change
 355          * that's due to these bits. This adds an implicit restriction that
 356          * no function will ever call notify_change with both ATTR_MODE and
 357          * ATTR_KILL_S*ID set.
 358          */
 359         if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
 360             (ia_valid & ATTR_MODE))
 361                 BUG();
 362
 363         if (ia_valid & ATTR_KILL_SUID) {
 364                 if (mode & S_ISUID) {
 365                         ia_valid = attr->ia_valid |= ATTR_MODE;
 366                         attr->ia_mode = (inode->i_mode & ~S_ISUID);
 367                 }
 368         }
 369         if (ia_valid & ATTR_KILL_SGID) {
 370                 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
 371                         if (!(ia_valid & ATTR_MODE)) {
 372                                 ia_valid = attr->ia_valid |= ATTR_MODE;
 373                                 attr->ia_mode = inode->i_mode;
 374                         }
 375                         attr->ia_mode &= ~S_ISGID;
 376                 }
 377         }
 378         if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
 379                 return 0;
 380
 381         /*
 382          * Verify that uid/gid changes are valid in the target
 383          * namespace of the superblock.
 384          */
 385         if (ia_valid & ATTR_UID &&
 386             !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
 387                 return -EOVERFLOW;
 388         if (ia_valid & ATTR_GID &&
 389             !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
 390                 return -EOVERFLOW;
 391
 392         /* Don't allow modifications of files with invalid uids or
 393          * gids unless those uids & gids are being made valid.
 394          */
 395         if (!(ia_valid & ATTR_UID) &&
 396             !uid_valid(i_uid_into_mnt(mnt_userns, inode)))
 397                 return -EOVERFLOW;
 398         if (!(ia_valid & ATTR_GID) &&
 399             !gid_valid(i_gid_into_mnt(mnt_userns, inode)))
 400                 return -EOVERFLOW;
 401
 402         error = security_inode_setattr(dentry, attr);
 403         if (error)
 404                 return error;
 405         error = try_break_deleg(inode, delegated_inode);
 406         if (error)
 407                 return error;
 408
 409         if (inode->i_op->setattr)
 410                 error = inode->i_op->setattr(mnt_userns, dentry, attr);
 411         else
 412                 error = simple_setattr(mnt_userns, dentry, attr);
 413
 414         if (!error) {
 415                 fsnotify_change(dentry, ia_valid);
 416                 ima_inode_post_setattr(mnt_userns, dentry);
 417                 evm_inode_post_setattr(dentry, ia_valid);
 418         }
 419
 420         return error;
 421 }
 422 EXPORT_SYMBOL(notify_change);