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