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/module.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
  17 /**
  18  * inode_change_ok - check if attribute changes to an inode are allowed
  19  * @inode:      inode to check
  20  * @attr:       attributes to change
  21  *
  22  * Check if we are allowed to change the attributes contained in @attr
  23  * in the given inode.  This includes the normal unix access permission
  24  * checks, as well as checks for rlimits and others.
  25  *
  26  * Should be called as the first thing in ->setattr implementations,
  27  * possibly after taking additional locks.
  28  */
  29 int inode_change_ok(const struct inode *inode, struct iattr *attr)
  30 {
  31         unsigned int ia_valid = attr->ia_valid;
  32
  33         /*
  34          * First check size constraints.  These can't be overriden using
  35          * ATTR_FORCE.
  36          */
  37         if (ia_valid & ATTR_SIZE) {
  38                 int error = inode_newsize_ok(inode, attr->ia_size);
  39                 if (error)
  40                         return error;
  41         }
  42
  43         /* If force is set do it anyway. */
  44         if (ia_valid & ATTR_FORCE)
  45                 return 0;
  46
  47         /* Make sure a caller can chown. */
  48         if ((ia_valid & ATTR_UID) &&
  49             (current_fsuid() != inode->i_uid ||
  50              attr->ia_uid != inode->i_uid) && !capable(CAP_CHOWN))
  51                 return -EPERM;
  52
  53         /* Make sure caller can chgrp. */
  54         if ((ia_valid & ATTR_GID) &&
  55             (current_fsuid() != inode->i_uid ||
  56             (!in_group_p(attr->ia_gid) && attr->ia_gid != inode->i_gid)) &&
  57             !capable(CAP_CHOWN))
  58                 return -EPERM;
  59
  60         /* Make sure a caller can chmod. */
  61         if (ia_valid & ATTR_MODE) {
  62                 if (!inode_owner_or_capable(inode))
  63                         return -EPERM;
  64                 /* Also check the setgid bit! */
  65                 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
  66                                 inode->i_gid) && !capable(CAP_FSETID))
  67                         attr->ia_mode &= ~S_ISGID;
  68         }
  69
  70         /* Check for setting the inode time. */
  71         if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
  72                 if (!inode_owner_or_capable(inode))
  73                         return -EPERM;
  74         }
  75
  76         return 0;
  77 }
  78 EXPORT_SYMBOL(inode_change_ok);
  79
  80 /**
  81  * inode_newsize_ok - may this inode be truncated to a given size
  82  * @inode:      the inode to be truncated
  83  * @offset:     the new size to assign to the inode
  84  * @Returns:    0 on success, -ve errno on failure
  85  *
  86  * inode_newsize_ok must be called with i_mutex held.
  87  *
  88  * inode_newsize_ok will check filesystem limits and ulimits to check that the
  89  * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
  90  * when necessary. Caller must not proceed with inode size change if failure is
  91  * returned. @inode must be a file (not directory), with appropriate
  92  * permissions to allow truncate (inode_newsize_ok does NOT check these
  93  * conditions).
  94  */
  95 int inode_newsize_ok(const struct inode *inode, loff_t offset)
  96 {
  97         if (inode->i_size < offset) {
  98                 unsigned long limit;
  99
 100                 limit = rlimit(RLIMIT_FSIZE);
 101                 if (limit != RLIM_INFINITY && offset > limit)
 102                         goto out_sig;
 103                 if (offset > inode->i_sb->s_maxbytes)
 104                         goto out_big;
 105         } else {
 106                 /*
 107                  * truncation of in-use swapfiles is disallowed - it would
 108                  * cause subsequent swapout to scribble on the now-freed
 109                  * blocks.
 110                  */
 111                 if (IS_SWAPFILE(inode))
 112                         return -ETXTBSY;
 113         }
 114
 115         return 0;
 116 out_sig:
 117         send_sig(SIGXFSZ, current, 0);
 118 out_big:
 119         return -EFBIG;
 120 }
 121 EXPORT_SYMBOL(inode_newsize_ok);
 122
 123 /**
 124  * setattr_copy - copy simple metadata updates into the generic inode
 125  * @inode:      the inode to be updated
 126  * @attr:       the new attributes
 127  *
 128  * setattr_copy must be called with i_mutex held.
 129  *
 130  * setattr_copy updates the inode's metadata with that specified
 131  * in attr. Noticeably missing is inode size update, which is more complex
 132  * as it requires pagecache updates.
 133  *
 134  * The inode is not marked as dirty after this operation. The rationale is
 135  * that for "simple" filesystems, the struct inode is the inode storage.
 136  * The caller is free to mark the inode dirty afterwards if needed.
 137  */
 138 void setattr_copy(struct inode *inode, const struct iattr *attr)
 139 {
 140         unsigned int ia_valid = attr->ia_valid;
 141
 142         if (ia_valid & ATTR_UID)
 143                 inode->i_uid = attr->ia_uid;
 144         if (ia_valid & ATTR_GID)
 145                 inode->i_gid = attr->ia_gid;
 146         if (ia_valid & ATTR_ATIME)
 147                 inode->i_atime = timespec_trunc(attr->ia_atime,
 148                                                 inode->i_sb->s_time_gran);
 149         if (ia_valid & ATTR_MTIME)
 150                 inode->i_mtime = timespec_trunc(attr->ia_mtime,
 151                                                 inode->i_sb->s_time_gran);
 152         if (ia_valid & ATTR_CTIME)
 153                 inode->i_ctime = timespec_trunc(attr->ia_ctime,
 154                                                 inode->i_sb->s_time_gran);
 155         if (ia_valid & ATTR_MODE) {
 156                 umode_t mode = attr->ia_mode;
 157
 158                 if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
 159                         mode &= ~S_ISGID;
 160                 inode->i_mode = mode;
 161         }
 162 }
 163 EXPORT_SYMBOL(setattr_copy);
 164
 165 int notify_change(struct dentry * dentry, struct iattr * attr)
 166 {
 167         struct inode *inode = dentry->d_inode;
 168         mode_t mode = inode->i_mode;
 169         int error;
 170         struct timespec now;
 171         unsigned int ia_valid = attr->ia_valid;
 172
 173         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
 174                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 175                         return -EPERM;
 176         }
 177
 178         if ((ia_valid & ATTR_MODE)) {
 179                 mode_t amode = attr->ia_mode;
 180                 /* Flag setting protected by i_mutex */
 181                 if (is_sxid(amode))
 182                         inode->i_flags &= ~S_NOSEC;
 183         }
 184
 185         now = current_fs_time(inode->i_sb);
 186
 187         attr->ia_ctime = now;
 188         if (!(ia_valid & ATTR_ATIME_SET))
 189                 attr->ia_atime = now;
 190         if (!(ia_valid & ATTR_MTIME_SET))
 191                 attr->ia_mtime = now;
 192         if (ia_valid & ATTR_KILL_PRIV) {
 193                 attr->ia_valid &= ~ATTR_KILL_PRIV;
 194                 ia_valid &= ~ATTR_KILL_PRIV;
 195                 error = security_inode_need_killpriv(dentry);
 196                 if (error > 0)
 197                         error = security_inode_killpriv(dentry);
 198                 if (error)
 199                         return error;
 200         }
 201
 202         /*
 203          * We now pass ATTR_KILL_S*ID to the lower level setattr function so
 204          * that the function has the ability to reinterpret a mode change
 205          * that's due to these bits. This adds an implicit restriction that
 206          * no function will ever call notify_change with both ATTR_MODE and
 207          * ATTR_KILL_S*ID set.
 208          */
 209         if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
 210             (ia_valid & ATTR_MODE))
 211                 BUG();
 212
 213         if (ia_valid & ATTR_KILL_SUID) {
 214                 if (mode & S_ISUID) {
 215                         ia_valid = attr->ia_valid |= ATTR_MODE;
 216                         attr->ia_mode = (inode->i_mode & ~S_ISUID);
 217                 }
 218         }
 219         if (ia_valid & ATTR_KILL_SGID) {
 220                 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
 221                         if (!(ia_valid & ATTR_MODE)) {
 222                                 ia_valid = attr->ia_valid |= ATTR_MODE;
 223                                 attr->ia_mode = inode->i_mode;
 224                         }
 225                         attr->ia_mode &= ~S_ISGID;
 226                 }
 227         }
 228         if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
 229                 return 0;
 230
 231         error = security_inode_setattr(dentry, attr);
 232         if (error)
 233                 return error;
 234
 235         if (ia_valid & ATTR_SIZE)
 236                 down_write(&dentry->d_inode->i_alloc_sem);
 237
 238         if (inode->i_op->setattr)
 239                 error = inode->i_op->setattr(dentry, attr);
 240         else
 241                 error = simple_setattr(dentry, attr);
 242
 243         if (ia_valid & ATTR_SIZE)
 244                 up_write(&dentry->d_inode->i_alloc_sem);
 245
 246         if (!error)
 247                 fsnotify_change(dentry, ia_valid);
 248
 249         return error;
 250 }
 251
 252 EXPORT_SYMBOL(notify_change);