fs/attr.c

   1 /*
   2  *  linux/fs/attr.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *  changes by Thomas Schoebel-Theuer
   6  */
   7
   8 #include <linux/export.h>
   9 #include <linux/time.h>
  10 #include <linux/mm.h>
  11 #include <linux/string.h>
  12 #include <linux/capability.h>
  13 #include <linux/fsnotify.h>
  14 #include <linux/fcntl.h>
  15 #include <linux/security.h>
  16 #include <linux/evm.h>
  17 #include <linux/ima.h>
  18
  19 static bool chown_ok(const struct inode *inode, kuid_t uid)
  20 {
  21         if (uid_eq(current_fsuid(), inode->i_uid) &&
  22             uid_eq(uid, inode->i_uid))
  23                 return true;
  24         if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  25                 return true;
  26         if (ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  27                 return true;
  28         return false;
  29 }
  30
  31 static bool chgrp_ok(const struct inode *inode, kgid_t gid)
  32 {
  33         if (uid_eq(current_fsuid(), inode->i_uid) &&
  34             (in_group_p(gid) || gid_eq(gid, inode->i_gid)))
  35                 return true;
  36         if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  37                 return true;
  38         if (ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  39                 return true;
  40         return false;
  41 }
  42
  43 /**
  44  * setattr_prepare - check if attribute changes to a dentry are allowed
  45  * @dentry:     dentry to check
  46  * @attr:       attributes to change
  47  *
  48  * Check if we are allowed to change the attributes contained in @attr
  49  * in the given dentry.  This includes the normal unix access permission
  50  * checks, as well as checks for rlimits and others. The function also clears
  51  * SGID bit from mode if user is not allowed to set it. Also file capabilities
  52  * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
  53  *
  54  * Should be called as the first thing in ->setattr implementations,
  55  * possibly after taking additional locks.
  56  */
  57 int setattr_prepare(struct dentry *dentry, struct iattr *attr)
  58 {
  59         struct inode *inode = d_inode(dentry);
  60         unsigned int ia_valid = attr->ia_valid;
  61
  62         /*
  63          * First check size constraints.  These can't be overriden using
  64          * ATTR_FORCE.
  65          */
  66         if (ia_valid & ATTR_SIZE) {
  67                 int error = inode_newsize_ok(inode, attr->ia_size);
  68                 if (error)
  69                         return error;
  70         }
  71
  72         /* If force is set do it anyway. */
  73         if (ia_valid & ATTR_FORCE)
  74                 goto kill_priv;
  75
  76         /* Make sure a caller can chown. */
  77         if ((ia_valid & ATTR_UID) && !chown_ok(inode, attr->ia_uid))
  78                 return -EPERM;
  79
  80         /* Make sure caller can chgrp. */
  81         if ((ia_valid & ATTR_GID) && !chgrp_ok(inode, attr->ia_gid))
  82                 return -EPERM;
  83
  84         /* Make sure a caller can chmod. */
  85         if (ia_valid & ATTR_MODE) {
  86                 if (!inode_owner_or_capable(inode))
  87                         return -EPERM;
  88                 /* Also check the setgid bit! */
  89                 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
  90                                 inode->i_gid) &&
  91                     !capable_wrt_inode_uidgid(inode, CAP_FSETID))
  92                         attr->ia_mode &= ~S_ISGID;
  93         }
  94
  95         /* Check for setting the inode time. */
  96         if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
  97                 if (!inode_owner_or_capable(inode))
  98                         return -EPERM;
  99         }
 100
 101 kill_priv:
 102         /* User has permission for the change */
 103         if (ia_valid & ATTR_KILL_PRIV) {
 104                 int error;
 105
 106                 error = security_inode_killpriv(dentry);
 107                 if (error)
 108                         return error;
 109         }
 110
 111         return 0;
 112 }
 113 EXPORT_SYMBOL(setattr_prepare);
 114
 115 /**
 116  * inode_newsize_ok - may this inode be truncated to a given size
 117  * @inode:      the inode to be truncated
 118  * @offset:     the new size to assign to the inode
 119  * @Returns:    0 on success, -ve errno on failure
 120  *
 121  * inode_newsize_ok must be called with i_mutex held.
 122  *
 123  * inode_newsize_ok will check filesystem limits and ulimits to check that the
 124  * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
 125  * when necessary. Caller must not proceed with inode size change if failure is
 126  * returned. @inode must be a file (not directory), with appropriate
 127  * permissions to allow truncate (inode_newsize_ok does NOT check these
 128  * conditions).
 129  */
 130 int inode_newsize_ok(const struct inode *inode, loff_t offset)
 131 {
 132         if (inode->i_size < offset) {
 133                 unsigned long limit;
 134
 135                 limit = rlimit(RLIMIT_FSIZE);
 136                 if (limit != RLIM_INFINITY && offset > limit)
 137                         goto out_sig;
 138                 if (offset > inode->i_sb->s_maxbytes)
 139                         goto out_big;
 140         } else {
 141                 /*
 142                  * truncation of in-use swapfiles is disallowed - it would
 143                  * cause subsequent swapout to scribble on the now-freed
 144                  * blocks.
 145                  */
 146                 if (IS_SWAPFILE(inode))
 147                         return -ETXTBSY;
 148         }
 149
 150         return 0;
 151 out_sig:
 152         send_sig(SIGXFSZ, current, 0);
 153 out_big:
 154         return -EFBIG;
 155 }
 156 EXPORT_SYMBOL(inode_newsize_ok);
 157
 158 /**
 159  * setattr_copy - copy simple metadata updates into the generic inode
 160  * @inode:      the inode to be updated
 161  * @attr:       the new attributes
 162  *
 163  * setattr_copy must be called with i_mutex held.
 164  *
 165  * setattr_copy updates the inode's metadata with that specified
 166  * in attr. Noticeably missing is inode size update, which is more complex
 167  * as it requires pagecache updates.
 168  *
 169  * The inode is not marked as dirty after this operation. The rationale is
 170  * that for "simple" filesystems, the struct inode is the inode storage.
 171  * The caller is free to mark the inode dirty afterwards if needed.
 172  */
 173 void setattr_copy(struct inode *inode, const struct iattr *attr)
 174 {
 175         unsigned int ia_valid = attr->ia_valid;
 176
 177         if (ia_valid & ATTR_UID)
 178                 inode->i_uid = attr->ia_uid;
 179         if (ia_valid & ATTR_GID)
 180                 inode->i_gid = attr->ia_gid;
 181         if (ia_valid & ATTR_ATIME)
 182                 inode->i_atime = timespec_trunc(attr->ia_atime,
 183                                                 inode->i_sb->s_time_gran);
 184         if (ia_valid & ATTR_MTIME)
 185                 inode->i_mtime = timespec_trunc(attr->ia_mtime,
 186                                                 inode->i_sb->s_time_gran);
 187         if (ia_valid & ATTR_CTIME)
 188                 inode->i_ctime = timespec_trunc(attr->ia_ctime,
 189                                                 inode->i_sb->s_time_gran);
 190         if (ia_valid & ATTR_MODE) {
 191                 umode_t mode = attr->ia_mode;
 192
 193                 if (!in_group_p(inode->i_gid) &&
 194                     !capable_wrt_inode_uidgid(inode, CAP_FSETID))
 195                         mode &= ~S_ISGID;
 196                 inode->i_mode = mode;
 197         }
 198 }
 199 EXPORT_SYMBOL(setattr_copy);
 200
 201 /**
 202  * notify_change - modify attributes of a filesytem object
 203  * @dentry:     object affected
 204  * @iattr:      new attributes
 205  * @delegated_inode: returns inode, if the inode is delegated
 206  *
 207  * The caller must hold the i_mutex on the affected object.
 208  *
 209  * If notify_change discovers a delegation in need of breaking,
 210  * it will return -EWOULDBLOCK and return a reference to the inode in
 211  * delegated_inode.  The caller should then break the delegation and
 212  * retry.  Because breaking a delegation may take a long time, the
 213  * caller should drop the i_mutex before doing so.
 214  *
 215  * Alternatively, a caller may pass NULL for delegated_inode.  This may
 216  * be appropriate for callers that expect the underlying filesystem not
 217  * to be NFS exported.  Also, passing NULL is fine for callers holding
 218  * the file open for write, as there can be no conflicting delegation in
 219  * that case.
 220  */
 221 int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **delegated_inode)
 222 {
 223         struct inode *inode = dentry->d_inode;
 224         umode_t mode = inode->i_mode;
 225         int error;
 226         struct timespec now;
 227         unsigned int ia_valid = attr->ia_valid;
 228
 229         WARN_ON_ONCE(!inode_is_locked(inode));
 230
 231         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
 232                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 233                         return -EPERM;
 234         }
 235
 236         /*
 237          * If utimes(2) and friends are called with times == NULL (or both
 238          * times are UTIME_NOW), then we need to check for write permission
 239          */
 240         if (ia_valid & ATTR_TOUCH) {
 241                 if (IS_IMMUTABLE(inode))
 242                         return -EPERM;
 243
 244                 if (!inode_owner_or_capable(inode)) {
 245                         error = inode_permission(inode, MAY_WRITE);
 246                         if (error)
 247                                 return error;
 248                 }
 249         }
 250
 251         if ((ia_valid & ATTR_MODE)) {
 252                 umode_t amode = attr->ia_mode;
 253                 /* Flag setting protected by i_mutex */
 254                 if (is_sxid(amode))
 255                         inode->i_flags &= ~S_NOSEC;
 256         }
 257
 258         now = current_time(inode);
 259
 260         attr->ia_ctime = now;
 261         if (!(ia_valid & ATTR_ATIME_SET))
 262                 attr->ia_atime = now;
 263         if (!(ia_valid & ATTR_MTIME_SET))
 264                 attr->ia_mtime = now;
 265         if (ia_valid & ATTR_KILL_PRIV) {
 266                 error = security_inode_need_killpriv(dentry);
 267                 if (error < 0)
 268                         return error;
 269                 if (error == 0)
 270                         ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
 271         }
 272
 273         /*
 274          * We now pass ATTR_KILL_S*ID to the lower level setattr function so
 275          * that the function has the ability to reinterpret a mode change
 276          * that's due to these bits. This adds an implicit restriction that
 277          * no function will ever call notify_change with both ATTR_MODE and
 278          * ATTR_KILL_S*ID set.
 279          */
 280         if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
 281             (ia_valid & ATTR_MODE))
 282                 BUG();
 283
 284         if (ia_valid & ATTR_KILL_SUID) {
 285                 if (mode & S_ISUID) {
 286                         ia_valid = attr->ia_valid |= ATTR_MODE;
 287                         attr->ia_mode = (inode->i_mode & ~S_ISUID);
 288                 }
 289         }
 290         if (ia_valid & ATTR_KILL_SGID) {
 291                 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
 292                         if (!(ia_valid & ATTR_MODE)) {
 293                                 ia_valid = attr->ia_valid |= ATTR_MODE;
 294                                 attr->ia_mode = inode->i_mode;
 295                         }
 296                         attr->ia_mode &= ~S_ISGID;
 297                 }
 298         }
 299         if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
 300                 return 0;
 301
 302         /*
 303          * Verify that uid/gid changes are valid in the target
 304          * namespace of the superblock.
 305          */
 306         if (ia_valid & ATTR_UID &&
 307             !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
 308                 return -EOVERFLOW;
 309         if (ia_valid & ATTR_GID &&
 310             !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
 311                 return -EOVERFLOW;
 312
 313         /* Don't allow modifications of files with invalid uids or
 314          * gids unless those uids & gids are being made valid.
 315          */
 316         if (!(ia_valid & ATTR_UID) && !uid_valid(inode->i_uid))
 317                 return -EOVERFLOW;
 318         if (!(ia_valid & ATTR_GID) && !gid_valid(inode->i_gid))
 319                 return -EOVERFLOW;
 320
 321         error = security_inode_setattr(dentry, attr);
 322         if (error)
 323                 return error;
 324         error = try_break_deleg(inode, delegated_inode);
 325         if (error)
 326                 return error;
 327
 328         if (inode->i_op->setattr)
 329                 error = inode->i_op->setattr(dentry, attr);
 330         else
 331                 error = simple_setattr(dentry, attr);
 332
 333         if (!error) {
 334                 fsnotify_change(dentry, ia_valid);
 335                 ima_inode_post_setattr(dentry);
 336                 evm_inode_post_setattr(dentry, ia_valid);
 337         }
 338
 339         return error;
 340 }
 341 EXPORT_SYMBOL(notify_change);