text: /*
   *  linux/fs/attr.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   *  changes by Thomas Schoebel-Theuer
   */
  
  #include <linux/export.h>
  #include <linux/time.h>
  #include <linux/mm.h>
  #include <linux/string.h>
  #include <linux/capability.h>
  #include <linux/fsnotify.h>
  #include <linux/fcntl.h>
  #include <linux/security.h>
  #include <linux/evm.h>
  #include <linux/ima.h>
  
  /**
   * inode_change_ok - check if attribute changes to an inode are allowed
   * @inode:	inode to check
   * @attr:	attributes to change
   *
   * Check if we are allowed to change the attributes contained in @attr
   * in the given inode.  This includes the normal unix access permission
   * checks, as well as checks for rlimits and others.
   *
   * Should be called as the first thing in ->setattr implementations,
   * possibly after taking additional locks.
   */
  int inode_change_ok(const struct inode *inode, struct iattr *attr)
  {
  	unsigned int ia_valid = attr->ia_valid;
  
  	/*
  	 * First check size constraints.  These can't be overriden using
  	 * ATTR_FORCE.
  	 */
  	if (ia_valid & ATTR_SIZE) {
  		int error = inode_newsize_ok(inode, attr->ia_size);
  		if (error)
  			return error;
  	}
  
  	/* If force is set do it anyway. */
  	if (ia_valid & ATTR_FORCE)
  		return 0;
  
  	/* Make sure a caller can chown. */
  	if ((ia_valid & ATTR_UID) &&
  	    (!uid_eq(current_fsuid(), inode->i_uid) ||
  	     !uid_eq(attr->ia_uid, inode->i_uid)) &&
  	    !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  		return -EPERM;
  
  	/* Make sure caller can chgrp. */
  	if ((ia_valid & ATTR_GID) &&
  	    (!uid_eq(current_fsuid(), inode->i_uid) ||
  	    (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) &&
  	    !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
  		return -EPERM;
  
  	/* Make sure a caller can chmod. */
  	if (ia_valid & ATTR_MODE) {
  		if (!inode_owner_or_capable(inode))
  			return -EPERM;
  		/* Also check the setgid bit! */
  		if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
  				inode->i_gid) &&
  		    !capable_wrt_inode_uidgid(inode, CAP_FSETID))
  			attr->ia_mode &= ~S_ISGID;
  	}
  
  	/* Check for setting the inode time. */
  	if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
  		if (!inode_owner_or_capable(inode))
  			return -EPERM;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL(inode_change_ok);
  
  /**
   * inode_newsize_ok - may this inode be truncated to a given size
   * @inode:	the inode to be truncated
   * @offset:	the new size to assign to the inode
   * @Returns:	0 on success, -ve errno on failure
   *
   * inode_newsize_ok must be called with i_mutex held.
   *
   * inode_newsize_ok will check filesystem limits and ulimits to check that the
   * new inode size is within limits. inode_newsize_ok will also send SIGXFSZ
   * when necessary. Caller must not proceed with inode size change if failure is
   * returned. @inode must be a file (not directory), with appropriate
   * permissions to allow truncate (inode_newsize_ok does NOT check these
   * conditions).
   */
  int inode_newsize_ok(const struct inode *inode, loff_t offset)
  {
  	if (inode->i_size < offset) {
  		unsigned long limit;
  
  		limit = rlimit(RLIMIT_FSIZE);
  		if (limit != RLIM_INFINITY && offset > limit)
  			goto out_sig;
  		if (offset > inode->i_sb->s_maxbytes)
  			goto out_big;
  	} else {
  		/*
  		 * truncation of in-use swapfiles is disallowed - it would
  		 * cause subsequent swapout to scribble on the now-freed
  		 * blocks.
  		 */
  		if (IS_SWAPFILE(inode))
  			return -ETXTBSY;
  	}
  
  	return 0;
  out_sig:
  	send_sig(SIGXFSZ, current, 0);
  out_big:
  	return -EFBIG;
  }
  EXPORT_SYMBOL(inode_newsize_ok);
  
  /**
   * setattr_copy - copy simple metadata updates into the generic inode
   * @inode:	the inode to be updated
   * @attr:	the new attributes
   *
   * setattr_copy must be called with i_mutex held.
   *
   * setattr_copy updates the inode's metadata with that specified
   * in attr. Noticeably missing is inode size update, which is more complex
   * as it requires pagecache updates.
   *
   * The inode is not marked as dirty after this operation. The rationale is
   * that for "simple" filesystems, the struct inode is the inode storage.
   * The caller is free to mark the inode dirty afterwards if needed.
   */
  void setattr_copy(struct inode *inode, const struct iattr *attr)
  {
  	unsigned int ia_valid = attr->ia_valid;
  
  	if (ia_valid & ATTR_UID)
  		inode->i_uid = attr->ia_uid;
  	if (ia_valid & ATTR_GID)
  		inode->i_gid = attr->ia_gid;
  	if (ia_valid & ATTR_ATIME)
  		inode->i_atime = timespec_trunc(attr->ia_atime,
  						inode->i_sb->s_time_gran);
  	if (ia_valid & ATTR_MTIME)
  		inode->i_mtime = timespec_trunc(attr->ia_mtime,
  						inode->i_sb->s_time_gran);
  	if (ia_valid & ATTR_CTIME)
  		inode->i_ctime = timespec_trunc(attr->ia_ctime,
  						inode->i_sb->s_time_gran);
  	if (ia_valid & ATTR_MODE) {
  		umode_t mode = attr->ia_mode;
  
  		if (!in_group_p(inode->i_gid) &&
  		    !capable_wrt_inode_uidgid(inode, CAP_FSETID))
  			mode &= ~S_ISGID;
  		inode->i_mode = mode;
  	}
  }
  EXPORT_SYMBOL(setattr_copy);
  
  int notify_change(struct dentry * dentry, struct iattr * attr)
  {
  	struct inode *inode = dentry->d_inode;
  	umode_t mode = inode->i_mode;
  	int error;
  	struct timespec now;
  	unsigned int ia_valid = attr->ia_valid;
  
  	WARN_ON_ONCE(!mutex_is_locked(&inode->i_mutex));
  
  	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
  		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
  			return -EPERM;
  	}
  
  	if ((ia_valid & ATTR_MODE)) {
  		umode_t amode = attr->ia_mode;
  		/* Flag setting protected by i_mutex */
  		if (is_sxid(amode))
  			inode->i_flags &= ~S_NOSEC;
  	}
  
  	now = current_fs_time(inode->i_sb);
  
  	attr->ia_ctime = now;
  	if (!(ia_valid & ATTR_ATIME_SET))
  		attr->ia_atime = now;
  	if (!(ia_valid & ATTR_MTIME_SET))
  		attr->ia_mtime = now;
  	if (ia_valid & ATTR_KILL_PRIV) {
  		attr->ia_valid &= ~ATTR_KILL_PRIV;
  		ia_valid &= ~ATTR_KILL_PRIV;
  		error = security_inode_need_killpriv(dentry);
  		if (error > 0)
  			error = security_inode_killpriv(dentry);
  		if (error)
  			return error;
  	}
  
  	/*
  	 * We now pass ATTR_KILL_S*ID to the lower level setattr function so
  	 * that the function has the ability to reinterpret a mode change
  	 * that's due to these bits. This adds an implicit restriction that
  	 * no function will ever call notify_change with both ATTR_MODE and
  	 * ATTR_KILL_S*ID set.
  	 */
  	if ((ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID)) &&
  	    (ia_valid & ATTR_MODE))
  		BUG();
  
  	if (ia_valid & ATTR_KILL_SUID) {
  		if (mode & S_ISUID) {
  			ia_valid = attr->ia_valid |= ATTR_MODE;
  			attr->ia_mode = (inode->i_mode & ~S_ISUID);
  		}
  	}
  	if (ia_valid & ATTR_KILL_SGID) {
  		if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
  			if (!(ia_valid & ATTR_MODE)) {
  				ia_valid = attr->ia_valid |= ATTR_MODE;
  				attr->ia_mode = inode->i_mode;
  			}
  			attr->ia_mode &= ~S_ISGID;
  		}
  	}
  	if (!(attr->ia_valid & ~(ATTR_KILL_SUID | ATTR_KILL_SGID)))
  		return 0;
  
  	error = security_inode_setattr(dentry, attr);
  	if (error)
  		return error;
  
  	if (inode->i_op->setattr)
  		error = inode->i_op->setattr(dentry, attr);
  	else
  		error = simple_setattr(dentry, attr);
  
  	if (!error) {
  		fsnotify_change(dentry, ia_valid);
  		ima_inode_post_setattr(dentry);
  		evm_inode_post_setattr(dentry, ia_valid);
  	}
  
  	return error;
  }
  EXPORT_SYMBOL(notify_change);
  