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