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