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  * setattr_prepare - check if attribute changes to a dentry are allowed
  23  * @dentry:     dentry to check
  24  * @attr:       attributes to change
  25  *
  26  * Check if we are allowed to change the attributes contained in @attr
  27  * in the given dentry.  This includes the normal unix access permission
  28  * checks, as well as checks for rlimits and others. The function also clears
  29  * SGID bit from mode if user is not allowed to set it. Also file capabilities
  30  * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
  31  *
  32  * Should be called as the first thing in ->setattr implementations,
  33  * possibly after taking additional locks.
  34  */
  35 int setattr_prepare(struct dentry *dentry, struct iattr *attr)
  36 {
  37         struct inode *inode = d_inode(dentry);
  38         unsigned int ia_valid = attr->ia_valid;
  39
  40         /*
  41          * First check size constraints.  These can't be overriden using
  42          * ATTR_FORCE.
  43          */
  44         if (ia_valid & ATTR_SIZE) {
  45                 int error = inode_newsize_ok(inode, attr->ia_size);
  46                 if (error)
  47                         return error;
  48         }
  49
  50         /* If force is set do it anyway. */
  51         if (ia_valid & ATTR_FORCE)
  52                 goto kill_priv;
  53
  54         /* Make sure a caller can chown. */
  55         if ((ia_valid & ATTR_UID) &&
  56             (!uid_eq(current_fsuid(), inode->i_uid) ||
  57              !uid_eq(attr->ia_uid, inode->i_uid)) &&
  58             !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  59                 return -EPERM;
  60
  61         /* Make sure caller can chgrp. */
  62         if ((ia_valid & ATTR_GID) &&
  63             (!uid_eq(current_fsuid(), inode->i_uid) ||
  64             (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) &&
  65             !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  66                 return -EPERM;
  67
  68         /* Make sure a caller can chmod. */
  69         if (ia_valid & ATTR_MODE) {
  70                 if (!inode_owner_or_capable(inode))
  71                         return -EPERM;
  72                 /* Also check the setgid bit! */
  73                 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
  74                                 inode->i_gid) &&
  75                     !capable_wrt_inode_uidgid(inode, CAP_FSETID))
  76                         attr->ia_mode &= ~S_ISGID;
  77         }
  78
  79         /* Check for setting the inode time. */
  80         if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
  81                 if (!inode_owner_or_capable(inode))
  82                         return -EPERM;
  83         }
  84
  85 kill_priv:
  86         /* User has permission for the change */
  87         if (ia_valid & ATTR_KILL_PRIV) {
  88                 int error;
  89
  90                 error = security_inode_killpriv(dentry);
  91                 if (error)
  92                         return error;
  93         }
  94
  95         return 0;
  96 }
  97 EXPORT_SYMBOL(setattr_prepare);
  98
  99 /**
 100  * inode_newsize_ok - may this inode be truncated to a given size
 101  * @inode:      the inode to be truncated
 102  * @offset:     the new size to assign to the inode
 103  * @Returns:    0 on success, -ve errno on failure
 104  *
 105  * inode_newsize_ok must be called with i_mutex held.
 106  *
 107  * inode_newsize_ok will check filesystem limits and ulimits to check that the
 108  * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
 109  * when necessary. Caller must not proceed with inode size change if failure is
 110  * returned. @inode must be a file (not directory), with appropriate
 111  * permissions to allow truncate (inode_newsize_ok does NOT check these
 112  * conditions).
 113  */
 114 int inode_newsize_ok(const struct inode *inode, loff_t offset)
 115 {
 116         if (inode->i_size < offset) {
 117                 unsigned long limit;
 118
 119                 limit = rlimit(RLIMIT_FSIZE);
 120                 if (limit != RLIM_INFINITY && offset > limit)
 121                         goto out_sig;
 122                 if (offset > inode->i_sb->s_maxbytes)
 123                         goto out_big;
 124         } else {
 125                 /*
 126                  * truncation of in-use swapfiles is disallowed - it would
 127                  * cause subsequent swapout to scribble on the now-freed
 128                  * blocks.
 129                  */
 130                 if (IS_SWAPFILE(inode))
 131                         return -ETXTBSY;
 132         }
 133
 134         return 0;
 135 out_sig:
 136         send_sig(SIGXFSZ, current, 0);
 137 out_big:
 138         return -EFBIG;
 139 }
 140 EXPORT_SYMBOL(inode_newsize_ok);
 141
 142 /**
 143  * setattr_copy - copy simple metadata updates into the generic inode
 144  * @inode:      the inode to be updated
 145  * @attr:       the new attributes
 146  *
 147  * setattr_copy must be called with i_mutex held.
 148  *
 149  * setattr_copy updates the inode's metadata with that specified
 150  * in attr. Noticeably missing is inode size update, which is more complex
 151  * as it requires pagecache updates.
 152  *
 153  * The inode is not marked as dirty after this operation. The rationale is
 154  * that for "simple" filesystems, the struct inode is the inode storage.
 155  * The caller is free to mark the inode dirty afterwards if needed.
 156  */
 157 void setattr_copy(struct inode *inode, const struct iattr *attr)
 158 {
 159         unsigned int ia_valid = attr->ia_valid;
 160
 161         if (ia_valid & ATTR_UID)
 162                 inode->i_uid = attr->ia_uid;
 163         if (ia_valid & ATTR_GID)
 164                 inode->i_gid = attr->ia_gid;
 165         if (ia_valid & ATTR_ATIME)
 166                 inode->i_atime = timespec_trunc(attr->ia_atime,
 167                                                 inode->i_sb->s_time_gran);
 168         if (ia_valid & ATTR_MTIME)
 169                 inode->i_mtime = timespec_trunc(attr->ia_mtime,
 170                                                 inode->i_sb->s_time_gran);
 171         if (ia_valid & ATTR_CTIME)
 172                 inode->i_ctime = timespec_trunc(attr->ia_ctime,
 173                                                 inode->i_sb->s_time_gran);
 174         if (ia_valid & ATTR_MODE) {
 175                 umode_t mode = attr->ia_mode;
 176
 177                 if (!in_group_p(inode->i_gid) &&
 178                     !capable_wrt_inode_uidgid(inode, CAP_FSETID))
 179                         mode &= ~S_ISGID;
 180                 inode->i_mode = mode;
 181         }
 182 }
 183 EXPORT_SYMBOL(setattr_copy);
 184
 185 /**
 186  * notify_change - modify attributes of a filesytem object
 187  * @dentry:     object affected
 188  * @iattr:      new attributes
 189  * @delegated_inode: returns inode, if the inode is delegated
 190  *
 191  * The caller must hold the i_mutex on the affected object.
 192  *
 193  * If notify_change discovers a delegation in need of breaking,
 194  * it will return -EWOULDBLOCK and return a reference to the inode in
 195  * delegated_inode.  The caller should then break the delegation and
 196  * retry.  Because breaking a delegation may take a long time, the
 197  * caller should drop the i_mutex before doing so.
 198  *
 199  * Alternatively, a caller may pass NULL for delegated_inode.  This may
 200  * be appropriate for callers that expect the underlying filesystem not
 201  * to be NFS exported.  Also, passing NULL is fine for callers holding
 202  * the file open for write, as there can be no conflicting delegation in
 203  * that case.
 204  */
 205 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
 206 {
 207         struct inode *inode = dentry->d_inode;
 208         umode_t mode = inode->i_mode;
 209         int error;
 210         struct timespec now;
 211         unsigned int ia_valid = attr->ia_valid;
 212
 213         WARN_ON_ONCE(!inode_is_locked(inode));
 214
 215         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
 216                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 217                         return -EPERM;
 218         }
 219
 220         /*
 221          * If utimes(2) and friends are called with times == NULL (or both
 222          * times are UTIME_NOW), then we need to check for write permission
 223          */
 224         if (ia_valid & ATTR_TOUCH) {
 225                 if (IS_IMMUTABLE(inode))
 226                         return -EPERM;
 227
 228                 if (!inode_owner_or_capable(inode)) {
 229                         error = inode_permission(inode, MAY_WRITE);
 230                         if (error)
 231                                 return error;
 232                 }
 233         }
 234
 235         if ((ia_valid & ATTR_MODE)) {
 236                 umode_t amode = attr->ia_mode;
 237                 /* Flag setting protected by i_mutex */
 238                 if (is_sxid(amode))
 239                         inode->i_flags &= ~S_NOSEC;
 240         }
 241
 242         now = current_time(inode);
 243
 244         attr->ia_ctime = now;
 245         if (!(ia_valid & ATTR_ATIME_SET))
 246                 attr->ia_atime = now;
 247         if (!(ia_valid & ATTR_MTIME_SET))
 248                 attr->ia_mtime = now;
 249         if (ia_valid & ATTR_KILL_PRIV) {
 250                 error = security_inode_need_killpriv(dentry);
 251                 if (error < 0)
 252                         return error;
 253                 if (error == 0)
 254                         ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
 255         }
 256
 257         /*
 258          * We now pass ATTR_KILL_S*ID to the lower level setattr function so
 259          * that the function has the ability to reinterpret a mode change
 260          * that's due to these bits. This adds an implicit restriction that
 261          * no function will ever call notify_change with both ATTR_MODE and
 262          * ATTR_KILL_S*ID set.
 263          */
 264         if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
 265             (ia_valid & ATTR_MODE))
 266                 BUG();
 267
 268         if (ia_valid & ATTR_KILL_SUID) {
 269                 if (mode & S_ISUID) {
 270                         ia_valid = attr->ia_valid |= ATTR_MODE;
 271                         attr->ia_mode = (inode->i_mode & ~S_ISUID);
 272                 }
 273         }
 274         if (ia_valid & ATTR_KILL_SGID) {
 275                 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
 276                         if (!(ia_valid & ATTR_MODE)) {
 277                                 ia_valid = attr->ia_valid |= ATTR_MODE;
 278                                 attr->ia_mode = inode->i_mode;
 279                         }
 280                         attr->ia_mode &= ~S_ISGID;
 281                 }
 282         }
 283         if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
 284                 return 0;
 285
 286         /*
 287          * Verify that uid/gid changes are valid in the target
 288          * namespace of the superblock.
 289          */
 290         if (ia_valid & ATTR_UID &&
 291             !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
 292                 return -EOVERFLOW;
 293         if (ia_valid & ATTR_GID &&
 294             !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
 295                 return -EOVERFLOW;
 296
 297         /* Don't allow modifications of files with invalid uids or
 298          * gids unless those uids & gids are being made valid.
 299          */
 300         if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
 301                 return -EOVERFLOW;
 302         if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
 303                 return -EOVERFLOW;
 304
 305         error = security_inode_setattr(dentry, attr);
 306         if (error)
 307                 return error;
 308         error = try_break_deleg(inode, delegated_inode);
 309         if (error)
 310                 return error;
 311
 312         if (inode->i_op->setattr)
 313                 error = inode->i_op->setattr(dentry, attr);
 314         else
 315                 error = simple_setattr(dentry, attr);
 316
 317         if (!error) {
 318                 fsnotify_change(dentry, ia_valid);
 319                 ima_inode_post_setattr(dentry);
 320                 evm_inode_post_setattr(dentry, ia_valid);
 321         }
 322
 323         return error;
 324 }
 325 EXPORT_SYMBOL(notify_change);