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