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