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)) && !capable(CAP_CHOWN))
  53                 return -EPERM;
  54
  55         /* Make sure caller can chgrp. */
  56         if ((ia_valid & ATTR_GID) &&
  57             (!uid_eq(current_fsuid(), inode->i_uid) ||
  58             (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) &&
  59             !capable(CAP_CHOWN))
  60                 return -EPERM;
  61
  62         /* Make sure a caller can chmod. */
  63         if (ia_valid & ATTR_MODE) {
  64                 if (!inode_owner_or_capable(inode))
  65                         return -EPERM;
  66                 /* Also check the setgid bit! */
  67                 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
  68                                 inode->i_gid) && !capable(CAP_FSETID))
  69                         attr->ia_mode &= ~S_ISGID;
  70         }
  71
  72         /* Check for setting the inode time. */
  73         if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
  74                 if (!inode_owner_or_capable(inode))
  75                         return -EPERM;
  76         }
  77
  78         return 0;
  79 }
  80 EXPORT_SYMBOL(inode_change_ok);
  81
  82 /**
  83  * inode_newsize_ok - may this inode be truncated to a given size
  84  * @inode:      the inode to be truncated
  85  * @offset:     the new size to assign to the inode
  86  * @Returns:    0 on success, -ve errno on failure
  87  *
  88  * inode_newsize_ok must be called with i_mutex held.
  89  *
  90  * inode_newsize_ok will check filesystem limits and ulimits to check that the
  91  * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
  92  * when necessary. Caller must not proceed with inode size change if failure is
  93  * returned. @inode must be a file (not directory), with appropriate
  94  * permissions to allow truncate (inode_newsize_ok does NOT check these
  95  * conditions).
  96  */
  97 int inode_newsize_ok(const struct inode *inode, loff_t offset)
  98 {
  99         if (inode->i_size < offset) {
 100                 unsigned long limit;
 101
 102                 limit = rlimit(RLIMIT_FSIZE);
 103                 if (limit != RLIM_INFINITY && offset > limit)
 104                         goto out_sig;
 105                 if (offset > inode->i_sb->s_maxbytes)
 106                         goto out_big;
 107         } else {
 108                 /*
 109                  * truncation of in-use swapfiles is disallowed - it would
 110                  * cause subsequent swapout to scribble on the now-freed
 111                  * blocks.
 112                  */
 113                 if (IS_SWAPFILE(inode))
 114                         return -ETXTBSY;
 115         }
 116
 117         return 0;
 118 out_sig:
 119         send_sig(SIGXFSZ, current, 0);
 120 out_big:
 121         return -EFBIG;
 122 }
 123 EXPORT_SYMBOL(inode_newsize_ok);
 124
 125 /**
 126  * setattr_copy - copy simple metadata updates into the generic inode
 127  * @inode:      the inode to be updated
 128  * @attr:       the new attributes
 129  *
 130  * setattr_copy must be called with i_mutex held.
 131  *
 132  * setattr_copy updates the inode's metadata with that specified
 133  * in attr. Noticeably missing is inode size update, which is more complex
 134  * as it requires pagecache updates.
 135  *
 136  * The inode is not marked as dirty after this operation. The rationale is
 137  * that for "simple" filesystems, the struct inode is the inode storage.
 138  * The caller is free to mark the inode dirty afterwards if needed.
 139  */
 140 void setattr_copy(struct inode *inode, const struct iattr *attr)
 141 {
 142         unsigned int ia_valid = attr->ia_valid;
 143
 144         if (ia_valid & ATTR_UID)
 145                 inode->i_uid = attr->ia_uid;
 146         if (ia_valid & ATTR_GID)
 147                 inode->i_gid = attr->ia_gid;
 148         if (ia_valid & ATTR_ATIME)
 149                 inode->i_atime = timespec_trunc(attr->ia_atime,
 150                                                 inode->i_sb->s_time_gran);
 151         if (ia_valid & ATTR_MTIME)
 152                 inode->i_mtime = timespec_trunc(attr->ia_mtime,
 153                                                 inode->i_sb->s_time_gran);
 154         if (ia_valid & ATTR_CTIME)
 155                 inode->i_ctime = timespec_trunc(attr->ia_ctime,
 156                                                 inode->i_sb->s_time_gran);
 157         if (ia_valid & ATTR_MODE) {
 158                 umode_t mode = attr->ia_mode;
 159
 160                 if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
 161                         mode &= ~S_ISGID;
 162                 inode->i_mode = mode;
 163         }
 164 }
 165 EXPORT_SYMBOL(setattr_copy);
 166
 167 int notify_change(struct dentry * dentry, struct iattr * attr)
 168 {
 169         struct inode *inode = dentry->d_inode;
 170         umode_t mode = inode->i_mode;
 171         int error;
 172         struct timespec now;
 173         unsigned int ia_valid = attr->ia_valid;
 174
 175         WARN_ON_ONCE(!mutex_is_locked(&inode->i_mutex));
 176
 177         if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
 178                 if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
 179                         return -EPERM;
 180         }
 181
 182         if ((ia_valid & ATTR_SIZE) && IS_I_VERSION(inode)) {
 183                 if (attr->ia_size != inode->i_size)
 184                         inode_inc_iversion(inode);
 185         }
 186
 187         if ((ia_valid & ATTR_MODE)) {
 188                 umode_t amode = attr->ia_mode;
 189                 /* Flag setting protected by i_mutex */
 190                 if (is_sxid(amode))
 191                         inode->i_flags &= ~S_NOSEC;
 192         }
 193
 194         now = current_fs_time(inode->i_sb);
 195
 196         attr->ia_ctime = now;
 197         if (!(ia_valid & ATTR_ATIME_SET))
 198                 attr->ia_atime = now;
 199         if (!(ia_valid & ATTR_MTIME_SET))
 200                 attr->ia_mtime = now;
 201         if (ia_valid & ATTR_KILL_PRIV) {
 202                 attr->ia_valid &= ~ATTR_KILL_PRIV;
 203                 ia_valid &= ~ATTR_KILL_PRIV;
 204                 error = security_inode_need_killpriv(dentry);
 205                 if (error > 0)
 206                         error = security_inode_killpriv(dentry);
 207                 if (error)
 208                         return error;
 209         }
 210
 211         /*
 212          * We now pass ATTR_KILL_S*ID to the lower level setattr function so
 213          * that the function has the ability to reinterpret a mode change
 214          * that's due to these bits. This adds an implicit restriction that
 215          * no function will ever call notify_change with both ATTR_MODE and
 216          * ATTR_KILL_S*ID set.
 217          */
 218         if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
 219             (ia_valid & ATTR_MODE))
 220                 BUG();
 221
 222         if (ia_valid & ATTR_KILL_SUID) {
 223                 if (mode & S_ISUID) {
 224                         ia_valid = attr->ia_valid |= ATTR_MODE;
 225                         attr->ia_mode = (inode->i_mode & ~S_ISUID);
 226                 }
 227         }
 228         if (ia_valid & ATTR_KILL_SGID) {
 229                 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
 230                         if (!(ia_valid & ATTR_MODE)) {
 231                                 ia_valid = attr->ia_valid |= ATTR_MODE;
 232                                 attr->ia_mode = inode->i_mode;
 233                         }
 234                         attr->ia_mode &= ~S_ISGID;
 235                 }
 236         }
 237         if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
 238                 return 0;
 239
 240         error = security_inode_setattr(dentry, attr);
 241         if (error)
 242                 return error;
 243
 244         if (inode->i_op->setattr)
 245                 error = inode->i_op->setattr(dentry, attr);
 246         else
 247                 error = simple_setattr(dentry, attr);
 248
 249         if (!error) {
 250                 fsnotify_change(dentry, ia_valid);
 251                 ima_inode_post_setattr(dentry);
 252                 evm_inode_post_setattr(dentry, ia_valid);
 253         }
 254
 255         return error;
 256 }
 257 EXPORT_SYMBOL(notify_change);