text: // SPDX-License-Identifier: GPL-2.0
  /*
   *  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/sched/signal.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>
  
  /**
   * chown_ok - verify permissions to chown inode
   * @mnt_userns:	user namespace of the mount @inode was found from
   * @inode:	inode to check permissions on
   * @uid:	uid to chown @inode to
   *
   * If the inode has been found through an idmapped mount the user namespace of
   * the vfsmount must be passed through @mnt_userns. This function will then
   * take care to map the inode according to @mnt_userns before checking
   * permissions. On non-idmapped mounts or if permission checking is to be
   * performed on the raw inode simply passs init_user_ns.
   */
  static bool chown_ok(struct user_namespace *mnt_userns,
  		     const struct inode *inode,
  		     kuid_t uid)
  {
  	kuid_t kuid = i_uid_into_mnt(mnt_userns, inode);
  	if (uid_eq(current_fsuid(), kuid) && uid_eq(uid, inode->i_uid))
  		return true;
  	if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_CHOWN))
  		return true;
  	if (uid_eq(kuid, INVALID_UID) &&
  	    ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  		return true;
  	return false;
  }
  
  /**
   * chgrp_ok - verify permissions to chgrp inode
   * @mnt_userns:	user namespace of the mount @inode was found from
   * @inode:	inode to check permissions on
   * @gid:	gid to chown @inode to
   *
   * If the inode has been found through an idmapped mount the user namespace of
   * the vfsmount must be passed through @mnt_userns. This function will then
   * take care to map the inode according to @mnt_userns before checking
   * permissions. On non-idmapped mounts or if permission checking is to be
   * performed on the raw inode simply passs init_user_ns.
   */
  static bool chgrp_ok(struct user_namespace *mnt_userns,
  		     const struct inode *inode, kgid_t gid)
  {
  	kgid_t kgid = i_gid_into_mnt(mnt_userns, inode);
  	if (uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) &&
  	    (in_group_p(gid) || gid_eq(gid, inode->i_gid)))
  		return true;
  	if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_CHOWN))
  		return true;
  	if (gid_eq(kgid, INVALID_GID) &&
  	    ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN))
  		return true;
  	return false;
  }
  
  /**
   * setattr_prepare - check if attribute changes to a dentry are allowed
   * @mnt_userns:	user namespace of the mount the inode was found from
   * @dentry:	dentry to check
   * @attr:	attributes to change
   *
   * Check if we are allowed to change the attributes contained in @attr
   * in the given dentry.  This includes the normal unix access permission
   * checks, as well as checks for rlimits and others. The function also clears
   * SGID bit from mode if user is not allowed to set it. Also file capabilities
   * and IMA extended attributes are cleared if ATTR_KILL_PRIV is set.
   *
   * If the inode has been found through an idmapped mount the user namespace of
   * the vfsmount must be passed through @mnt_userns. This function will then
   * take care to map the inode according to @mnt_userns before checking
   * permissions. On non-idmapped mounts or if permission checking is to be
   * performed on the raw inode simply passs init_user_ns.
   *
   * Should be called as the first thing in ->setattr implementations,
   * possibly after taking additional locks.
   */
  int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry,
  		    struct iattr *attr)
  {
  	struct inode *inode = d_inode(dentry);
  	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)
  		goto kill_priv;
  
  	/* Make sure a caller can chown. */
  	if ((ia_valid & ATTR_UID) && !chown_ok(mnt_userns, inode, attr->ia_uid))
  		return -EPERM;
  
  	/* Make sure caller can chgrp. */
  	if ((ia_valid & ATTR_GID) && !chgrp_ok(mnt_userns, inode, attr->ia_gid))
  		return -EPERM;
  
  	/* Make sure a caller can chmod. */
  	if (ia_valid & ATTR_MODE) {
  		if (!inode_owner_or_capable(mnt_userns, inode))
  			return -EPERM;
  		/* Also check the setgid bit! */
                 if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
                                  i_gid_into_mnt(mnt_userns, inode)) &&
                      !capable_wrt_inode_uidgid(mnt_userns, 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(mnt_userns, inode))
  			return -EPERM;
  	}
  
  kill_priv:
  	/* User has permission for the change */
  	if (ia_valid & ATTR_KILL_PRIV) {
  		int error;
  
  		error = security_inode_killpriv(mnt_userns, dentry);
  		if (error)
  			return error;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL(setattr_prepare);
  
  /**
   * 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
   *
   * 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).
   *
   * Return: 0 on success, -ve errno on failure
   */
  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
   * @mnt_userns:	user namespace of the mount the inode was found from
   * @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 on idmapped mounts. If file ownership is changed setattr_copy
   * doesn't map ia_uid and ia_gid. It will asssume the caller has already
   * provided the intended values. Necessary permission checks to determine
   * whether or not the S_ISGID property needs to be removed are performed with
   * the correct idmapped mount permission helpers.
   * Noticeably missing is inode size update, which is more complex
   * as it requires pagecache updates.
   *
   * If the inode has been found through an idmapped mount the user namespace of
   * the vfsmount must be passed through @mnt_userns. This function will then
   * take care to map the inode according to @mnt_userns before checking
   * permissions. On non-idmapped mounts or if permission checking is to be
   * performed on the raw inode simply passs init_user_ns.
   *
   * 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 user_namespace *mnt_userns, 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 = attr->ia_atime;
  	if (ia_valid & ATTR_MTIME)
  		inode->i_mtime = attr->ia_mtime;
  	if (ia_valid & ATTR_CTIME)
  		inode->i_ctime = attr->ia_ctime;
  	if (ia_valid & ATTR_MODE) {
  		umode_t mode = attr->ia_mode;
  		kgid_t kgid = i_gid_into_mnt(mnt_userns, inode);
  		if (!in_group_p(kgid) &&
  		    !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
  			mode &= ~S_ISGID;
  		inode->i_mode = mode;
  	}
  }
  EXPORT_SYMBOL(setattr_copy);
  
  int may_setattr(struct user_namespace *mnt_userns, struct inode *inode,
  		unsigned int ia_valid)
  {
  	int error;
  
  	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
  		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
  			return -EPERM;
  	}
  
  	/*
  	 * If utimes(2) and friends are called with times == NULL (or both
  	 * times are UTIME_NOW), then we need to check for write permission
  	 */
  	if (ia_valid & ATTR_TOUCH) {
  		if (IS_IMMUTABLE(inode))
  			return -EPERM;
  
  		if (!inode_owner_or_capable(mnt_userns, inode)) {
  			error = inode_permission(mnt_userns, inode, MAY_WRITE);
  			if (error)
  				return error;
  		}
  	}
  	return 0;
  }
  EXPORT_SYMBOL(may_setattr);
  
  /**
   * notify_change - modify attributes of a filesytem object
   * @mnt_userns:	user namespace of the mount the inode was found from
   * @dentry:	object affected
   * @attr:	new attributes
   * @delegated_inode: returns inode, if the inode is delegated
   *
   * The caller must hold the i_mutex on the affected object.
   *
   * If notify_change discovers a delegation in need of breaking,
   * it will return -EWOULDBLOCK and return a reference to the inode in
   * delegated_inode.  The caller should then break the delegation and
   * retry.  Because breaking a delegation may take a long time, the
   * caller should drop the i_mutex before doing so.
   *
   * If file ownership is changed notify_change() doesn't map ia_uid and
   * ia_gid. It will asssume the caller has already provided the intended values.
   *
   * Alternatively, a caller may pass NULL for delegated_inode.  This may
   * be appropriate for callers that expect the underlying filesystem not
   * to be NFS exported.  Also, passing NULL is fine for callers holding
   * the file open for write, as there can be no conflicting delegation in
   * that case.
   *
   * If the inode has been found through an idmapped mount the user namespace of
   * the vfsmount must be passed through @mnt_userns. This function will then
   * take care to map the inode according to @mnt_userns before checking
   * permissions. On non-idmapped mounts or if permission checking is to be
   * performed on the raw inode simply passs init_user_ns.
   */
  int notify_change(struct user_namespace *mnt_userns, struct dentry *dentry,
  		  struct iattr *attr, struct inode **delegated_inode)
  {
  	struct inode *inode = dentry->d_inode;
  	umode_t mode = inode->i_mode;
  	int error;
  	struct timespec64 now;
  	unsigned int ia_valid = attr->ia_valid;
  
  	WARN_ON_ONCE(!inode_is_locked(inode));
  
  	error = may_setattr(mnt_userns, inode, ia_valid);
  	if (error)
  		return error;
  
  	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_time(inode);
  
  	attr->ia_ctime = now;
  	if (!(ia_valid & ATTR_ATIME_SET))
  		attr->ia_atime = now;
  	else
  		attr->ia_atime = timestamp_truncate(attr->ia_atime, inode);
  	if (!(ia_valid & ATTR_MTIME_SET))
  		attr->ia_mtime = now;
  	else
  		attr->ia_mtime = timestamp_truncate(attr->ia_mtime, inode);
  
  	if (ia_valid & ATTR_KILL_PRIV) {
  		error = security_inode_need_killpriv(dentry);
  		if (error < 0)
  			return error;
  		if (error == 0)
  			ia_valid = attr->ia_valid &= ~ATTR_KILL_PRIV;
  	}
  
  	/*
  	 * 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;
  
  	/*
  	 * Verify that uid/gid changes are valid in the target
  	 * namespace of the superblock.
  	 */
  	if (ia_valid & ATTR_UID &&
  	    !kuid_has_mapping(inode->i_sb->s_user_ns, attr->ia_uid))
  		return -EOVERFLOW;
  	if (ia_valid & ATTR_GID &&
  	    !kgid_has_mapping(inode->i_sb->s_user_ns, attr->ia_gid))
  		return -EOVERFLOW;
  
  	/* Don't allow modifications of files with invalid uids or
  	 * gids unless those uids & gids are being made valid.
  	 */
  	if (!(ia_valid & ATTR_UID) &&
  	    !uid_valid(i_uid_into_mnt(mnt_userns, inode)))
  		return -EOVERFLOW;
  	if (!(ia_valid & ATTR_GID) &&
  	    !gid_valid(i_gid_into_mnt(mnt_userns, inode)))
  		return -EOVERFLOW;
  
  	error = security_inode_setattr(dentry, attr);
  	if (error)
  		return error;
  	error = try_break_deleg(inode, delegated_inode);
  	if (error)
  		return error;
  
  	if (inode->i_op->setattr)
  		error = inode->i_op->setattr(mnt_userns, dentry, attr);
  	else
  		error = simple_setattr(mnt_userns, dentry, attr);
  
  	if (!error) {
  		fsnotify_change(dentry, ia_valid);
  		ima_inode_post_setattr(mnt_userns, dentry);
  		evm_inode_post_setattr(dentry, ia_valid);
  	}
  
  	return error;
  }
  EXPORT_SYMBOL(notify_change);
  