File: access_check.c

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/*
   Unix SMB/CIFS implementation.

   Copyright (C) Andrew Tridgell 2004
   Copyright (C) Gerald Carter 2005
   Copyright (C) Volker Lendecke 2007
   Copyright (C) Jeremy Allison 2008
   Copyright (C) Andrew Bartlett 2010

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "libcli/security/security.h"

/* Map generic access rights to object specific rights.  This technique is
   used to give meaning to assigning read, write, execute and all access to
   objects.  Each type of object has its own mapping of generic to object
   specific access rights. */

void se_map_generic(uint32_t *access_mask, const struct generic_mapping *mapping)
{
	uint32_t old_mask = *access_mask;

	if (*access_mask & GENERIC_READ_ACCESS) {
		*access_mask &= ~GENERIC_READ_ACCESS;
		*access_mask |= mapping->generic_read;
	}

	if (*access_mask & GENERIC_WRITE_ACCESS) {
		*access_mask &= ~GENERIC_WRITE_ACCESS;
		*access_mask |= mapping->generic_write;
	}

	if (*access_mask & GENERIC_EXECUTE_ACCESS) {
		*access_mask &= ~GENERIC_EXECUTE_ACCESS;
		*access_mask |= mapping->generic_execute;
	}

	if (*access_mask & GENERIC_ALL_ACCESS) {
		*access_mask &= ~GENERIC_ALL_ACCESS;
		*access_mask |= mapping->generic_all;
	}

	if (old_mask != *access_mask) {
		DEBUG(10, ("se_map_generic(): mapped mask 0x%08x to 0x%08x\n",
			   old_mask, *access_mask));
	}
}

/* Map generic access rights to object specific rights for all the ACE's
 * in a security_acl.
 */

void security_acl_map_generic(struct security_acl *sa,
				const struct generic_mapping *mapping)
{
	unsigned int i;

	if (!sa) {
		return;
	}

	for (i = 0; i < sa->num_aces; i++) {
		se_map_generic(&sa->aces[i].access_mask, mapping);
	}
}

/* Map standard access rights to object specific rights.  This technique is
   used to give meaning to assigning read, write, execute and all access to
   objects.  Each type of object has its own mapping of standard to object
   specific access rights. */

void se_map_standard(uint32_t *access_mask, const struct standard_mapping *mapping)
{
	uint32_t old_mask = *access_mask;

	if (*access_mask & SEC_STD_READ_CONTROL) {
		*access_mask &= ~SEC_STD_READ_CONTROL;
		*access_mask |= mapping->std_read;
	}

	if (*access_mask & (SEC_STD_DELETE|SEC_STD_WRITE_DAC|SEC_STD_WRITE_OWNER|SEC_STD_SYNCHRONIZE)) {
		*access_mask &= ~(SEC_STD_DELETE|SEC_STD_WRITE_DAC|SEC_STD_WRITE_OWNER|SEC_STD_SYNCHRONIZE);
		*access_mask |= mapping->std_all;
	}

	if (old_mask != *access_mask) {
		DEBUG(10, ("se_map_standard(): mapped mask 0x%08x to 0x%08x\n",
			   old_mask, *access_mask));
	}
}

/*
  perform a SEC_FLAG_MAXIMUM_ALLOWED access check
*/
static uint32_t access_check_max_allowed(const struct security_descriptor *sd,
					const struct security_token *token)
{
	uint32_t denied = 0, granted = 0;
	unsigned i;

	if (security_token_has_sid(token, sd->owner_sid)) {
		granted |= SEC_STD_WRITE_DAC | SEC_STD_READ_CONTROL;
	}

	if (sd->dacl == NULL) {
		return granted & ~denied;
	}

	for (i = 0;i<sd->dacl->num_aces; i++) {
		struct security_ace *ace = &sd->dacl->aces[i];

		if (ace->flags & SEC_ACE_FLAG_INHERIT_ONLY) {
			continue;
		}

		if (!security_token_has_sid(token, &ace->trustee)) {
			continue;
		}

		switch (ace->type) {
		case SEC_ACE_TYPE_ACCESS_ALLOWED:
			granted |= ace->access_mask;
			break;
		case SEC_ACE_TYPE_ACCESS_DENIED:
		case SEC_ACE_TYPE_ACCESS_DENIED_OBJECT:
			denied |= ace->access_mask;
			break;
		default:	/* Other ACE types not handled/supported */
			break;
		}
	}

	return granted & ~denied;
}

/*
  The main entry point for access checking. If returning ACCESS_DENIED
  this function returns the denied bits in the uint32_t pointed
  to by the access_granted pointer.
*/
NTSTATUS se_access_check(const struct security_descriptor *sd,
			  const struct security_token *token,
			  uint32_t access_desired,
			  uint32_t *access_granted)
{
	uint32_t i;
	uint32_t bits_remaining;
	uint32_t explicitly_denied_bits = 0;
	/*
	 * Up until Windows Server 2008, owner always had these rights. Now
	 * we have to use Owner Rights perms if they are on the file.
	 *
	 * In addition we have to accumulate these bits and apply them
	 * correctly. See bug #8795
	 */
	uint32_t owner_rights_allowed = 0;
	uint32_t owner_rights_denied = 0;
	bool owner_rights_default = true;

	*access_granted = access_desired;
	bits_remaining = access_desired;

	/* handle the maximum allowed flag */
	if (access_desired & SEC_FLAG_MAXIMUM_ALLOWED) {
		uint32_t orig_access_desired = access_desired;

		access_desired |= access_check_max_allowed(sd, token);
		access_desired &= ~SEC_FLAG_MAXIMUM_ALLOWED;
		*access_granted = access_desired;
		bits_remaining = access_desired;

		DEBUG(10,("se_access_check: MAX desired = 0x%x, granted = 0x%x, remaining = 0x%x\n",
			orig_access_desired,
			*access_granted,
			bits_remaining));
	}

	/* a NULL dacl allows access */
	if ((sd->type & SEC_DESC_DACL_PRESENT) && sd->dacl == NULL) {
		*access_granted = access_desired;
		return NT_STATUS_OK;
	}

	if (sd->dacl == NULL) {
		goto done;
	}

	/* check each ace in turn. */
	for (i=0; bits_remaining && i < sd->dacl->num_aces; i++) {
		struct security_ace *ace = &sd->dacl->aces[i];

		if (ace->flags & SEC_ACE_FLAG_INHERIT_ONLY) {
			continue;
		}

		/*
		 * We need the Owner Rights permissions to ensure we
		 * give or deny the correct permissions to the owner. Replace
		 * owner_rights with the perms here if it is present.
		 *
		 * We don't care if we are not the owner because that is taken
		 * care of below when we check if our token has the owner SID.
		 *
		 */
		if (dom_sid_equal(&ace->trustee, &global_sid_Owner_Rights)) {
			if (ace->type == SEC_ACE_TYPE_ACCESS_ALLOWED) {
				owner_rights_allowed |= ace->access_mask;
				owner_rights_default = false;
			} else if (ace->type == SEC_ACE_TYPE_ACCESS_DENIED) {
				owner_rights_denied |= (bits_remaining & ace->access_mask);
				owner_rights_default = false;
			}
			continue;
		}

		if (!security_token_has_sid(token, &ace->trustee)) {
			continue;
		}

		switch (ace->type) {
		case SEC_ACE_TYPE_ACCESS_ALLOWED:
			bits_remaining &= ~ace->access_mask;
			break;
		case SEC_ACE_TYPE_ACCESS_DENIED:
		case SEC_ACE_TYPE_ACCESS_DENIED_OBJECT:
			explicitly_denied_bits |= (bits_remaining & ace->access_mask);
			break;
		default:	/* Other ACE types not handled/supported */
			break;
		}
	}

	/* Explicitly denied bits always override */
	bits_remaining |= explicitly_denied_bits;

	/* The owner always gets owner rights as defined above. */
	if (security_token_has_sid(token, sd->owner_sid)) {
		if (owner_rights_default) {
			/*
			 * Just remove them, no need to check if they are
			 * there.
			 */
			bits_remaining &= ~(SEC_STD_WRITE_DAC |
						SEC_STD_READ_CONTROL);
		} else {
			bits_remaining &= ~owner_rights_allowed;
			bits_remaining |= owner_rights_denied;
		}
	}

	/*
	 * We check privileges here because they override even DENY entries.
	 */

	/* Does the user have the privilege to gain SEC_PRIV_SECURITY? */
	if (bits_remaining & SEC_FLAG_SYSTEM_SECURITY) {
		if (security_token_has_privilege(token, SEC_PRIV_SECURITY)) {
			bits_remaining &= ~SEC_FLAG_SYSTEM_SECURITY;
		} else {
			return NT_STATUS_PRIVILEGE_NOT_HELD;
		}
	}

	if ((bits_remaining & SEC_STD_WRITE_OWNER) &&
	     security_token_has_privilege(token, SEC_PRIV_TAKE_OWNERSHIP)) {
		bits_remaining &= ~(SEC_STD_WRITE_OWNER);
	}

done:
	if (bits_remaining != 0) {
		*access_granted = bits_remaining;
		return NT_STATUS_ACCESS_DENIED;
	}

	return NT_STATUS_OK;
}

/*
  The main entry point for access checking FOR THE FILE SERVER ONLY !
  If returning ACCESS_DENIED this function returns the denied bits in
  the uint32_t pointed to by the access_granted pointer.
*/
NTSTATUS se_file_access_check(const struct security_descriptor *sd,
			  const struct security_token *token,
			  bool priv_open_requested,
			  uint32_t access_desired,
			  uint32_t *access_granted)
{
	uint32_t bits_remaining;
	NTSTATUS status;

	if (!priv_open_requested) {
		/* Fall back to generic se_access_check(). */
		return se_access_check(sd,
				token,
				access_desired,
				access_granted);
	}

	/*
	 * We need to handle the maximum allowed flag
	 * outside of se_access_check(), as we need to
	 * add in the access allowed by the privileges
	 * as well.
	 */

	if (access_desired & SEC_FLAG_MAXIMUM_ALLOWED) {
		uint32_t orig_access_desired = access_desired;

		access_desired |= access_check_max_allowed(sd, token);
		access_desired &= ~SEC_FLAG_MAXIMUM_ALLOWED;

		if (security_token_has_privilege(token, SEC_PRIV_BACKUP)) {
			access_desired |= SEC_RIGHTS_PRIV_BACKUP;
		}

		if (security_token_has_privilege(token, SEC_PRIV_RESTORE)) {
			access_desired |= SEC_RIGHTS_PRIV_RESTORE;
		}

		DEBUG(10,("se_file_access_check: MAX desired = 0x%x "
			"mapped to 0x%x\n",
			orig_access_desired,
			access_desired));
	}

	status = se_access_check(sd,
				token,
				access_desired,
				access_granted);

	if (!NT_STATUS_EQUAL(status, NT_STATUS_ACCESS_DENIED)) {
		return status;
	}

	bits_remaining = *access_granted;

	/* Check if we should override with privileges. */
	if ((bits_remaining & SEC_RIGHTS_PRIV_BACKUP) &&
	    security_token_has_privilege(token, SEC_PRIV_BACKUP)) {
		bits_remaining &= ~(SEC_RIGHTS_PRIV_BACKUP);
	}
	if ((bits_remaining & SEC_RIGHTS_PRIV_RESTORE) &&
	    security_token_has_privilege(token, SEC_PRIV_RESTORE)) {
		bits_remaining &= ~(SEC_RIGHTS_PRIV_RESTORE);
	}
	if (bits_remaining != 0) {
		*access_granted = bits_remaining;
		return NT_STATUS_ACCESS_DENIED;
	}

	return NT_STATUS_OK;
}

static const struct GUID *get_ace_object_type(struct security_ace *ace)
{
	if (ace->object.object.flags & SEC_ACE_OBJECT_TYPE_PRESENT) {
		return &ace->object.object.type.type;
	}

	return NULL;
}

/**
 * Evaluates access rights specified in a object-specific ACE for an AD object.
 * This logic corresponds to MS-ADTS 5.1.3.3.3 Checking Object-Specific Access.
 * @param[in] ace - the ACE being processed
 * @param[in/out] tree - remaining_access gets updated for the tree
 * @param[out] grant_access - set to true if the ACE grants sufficient access
 *                            rights to the object/attribute
 * @returns NT_STATUS_OK, unless access was denied
 */
static NTSTATUS check_object_specific_access(struct security_ace *ace,
					     struct object_tree *tree,
					     bool *grant_access)
{
	struct object_tree *node = NULL;
	const struct GUID *type = NULL;

	*grant_access = false;

	/* if no tree was supplied, we can't do object-specific access checks */
	if (!tree) {
		return NT_STATUS_OK;
	}

	/* Get the ObjectType GUID this ACE applies to */
	type = get_ace_object_type(ace);

	/*
	 * If the ACE doesn't have a type, then apply it to the whole tree, i.e.
	 * treat 'OA' ACEs as 'A' and 'OD' as 'D'
	 */
	if (!type) {
		node = tree;
	} else {

		/* skip it if the ACE's ObjectType GUID is not in the tree */
		node = get_object_tree_by_GUID(tree, type);
		if (!node) {
			return NT_STATUS_OK;
		}
	}

	if (ace->type == SEC_ACE_TYPE_ACCESS_ALLOWED_OBJECT) {

		/* apply the access rights to this node, and any children */
		object_tree_modify_access(node, ace->access_mask);

		/*
		 * Currently all nodes in the tree request the same access mask,
		 * so we can use any node to check if processing this ACE now
		 * means the requested access has been granted
		 */
		if (node->remaining_access == 0) {
			*grant_access = true;
			return NT_STATUS_OK;
		}

		/*
		 * As per 5.1.3.3.4 Checking Control Access Right-Based Access,
		 * if the CONTROL_ACCESS right is present, then we can grant
		 * access and stop any further access checks
		 */
		if (ace->access_mask & SEC_ADS_CONTROL_ACCESS) {
			*grant_access = true;
			return NT_STATUS_OK;
		}
	} else {

		/* this ACE denies access to the requested object/attribute */
		if (node->remaining_access & ace->access_mask){
			return NT_STATUS_ACCESS_DENIED;
		}
	}
	return NT_STATUS_OK;
}

/**
 * @brief Perform directoryservice (DS) related access checks for a given user
 *
 * Perform DS access checks for the user represented by its security_token, on
 * the provided security descriptor. If an tree associating GUID and access
 * required is provided then object access (OA) are checked as well. *
 * @param[in]   sd             The security descritor against which the required
 *                             access are requested
 *
 * @param[in]   token          The security_token associated with the user to
 *                             test
 *
 * @param[in]   access_desired A bitfield of rights that must be granted for the
 *                             given user in the specified SD.
 *
 * If one
 * of the entry in the tree grants all the requested rights for the given GUID
 * FIXME
 * tree can be null if not null it's the
 * Lots of code duplication, it will ve united in just one
 * function eventually */

NTSTATUS sec_access_check_ds(const struct security_descriptor *sd,
			     const struct security_token *token,
			     uint32_t access_desired,
			     uint32_t *access_granted,
			     struct object_tree *tree,
			     struct dom_sid *replace_sid)
{
	uint32_t i;
	uint32_t bits_remaining;
	struct dom_sid self_sid;

	dom_sid_parse(SID_NT_SELF, &self_sid);

	*access_granted = access_desired;
	bits_remaining = access_desired;

	/* handle the maximum allowed flag */
	if (access_desired & SEC_FLAG_MAXIMUM_ALLOWED) {
		access_desired |= access_check_max_allowed(sd, token);
		access_desired &= ~SEC_FLAG_MAXIMUM_ALLOWED;
		*access_granted = access_desired;
		bits_remaining = access_desired;
	}

	if (access_desired & SEC_FLAG_SYSTEM_SECURITY) {
		if (security_token_has_privilege(token, SEC_PRIV_SECURITY)) {
			bits_remaining &= ~SEC_FLAG_SYSTEM_SECURITY;
		} else {
			return NT_STATUS_PRIVILEGE_NOT_HELD;
		}
	}

	/* the owner always gets SEC_STD_WRITE_DAC and SEC_STD_READ_CONTROL */
	if ((bits_remaining & (SEC_STD_WRITE_DAC|SEC_STD_READ_CONTROL)) &&
	    security_token_has_sid(token, sd->owner_sid)) {
		bits_remaining &= ~(SEC_STD_WRITE_DAC|SEC_STD_READ_CONTROL);
	}

	/* SEC_PRIV_TAKE_OWNERSHIP grants SEC_STD_WRITE_OWNER */
	if ((bits_remaining & (SEC_STD_WRITE_OWNER)) &&
	    security_token_has_privilege(token, SEC_PRIV_TAKE_OWNERSHIP)) {
		bits_remaining &= ~(SEC_STD_WRITE_OWNER);
	}

	/* a NULL dacl allows access */
	if ((sd->type & SEC_DESC_DACL_PRESENT) && sd->dacl == NULL) {
		*access_granted = access_desired;
		return NT_STATUS_OK;
	}

	if (sd->dacl == NULL) {
		goto done;
	}

	/* check each ace in turn. */
	for (i=0; bits_remaining && i < sd->dacl->num_aces; i++) {
		struct dom_sid *trustee;
		struct security_ace *ace = &sd->dacl->aces[i];
		NTSTATUS status;
		bool grant_access = false;

		if (ace->flags & SEC_ACE_FLAG_INHERIT_ONLY) {
			continue;
		}

		if (dom_sid_equal(&ace->trustee, &self_sid) && replace_sid) {
			trustee = replace_sid;
		} else {
			trustee = &ace->trustee;
		}

		if (!security_token_has_sid(token, trustee)) {
			continue;
		}

		switch (ace->type) {
		case SEC_ACE_TYPE_ACCESS_ALLOWED:
			if (tree) {
				object_tree_modify_access(tree, ace->access_mask);
			}

			bits_remaining &= ~ace->access_mask;
			break;
		case SEC_ACE_TYPE_ACCESS_DENIED:
			if (bits_remaining & ace->access_mask) {
				return NT_STATUS_ACCESS_DENIED;
			}
			break;
		case SEC_ACE_TYPE_ACCESS_DENIED_OBJECT:
		case SEC_ACE_TYPE_ACCESS_ALLOWED_OBJECT:
			status = check_object_specific_access(ace, tree,
							      &grant_access);

			if (!NT_STATUS_IS_OK(status)) {
				return status;
			}

			if (grant_access) {
				return NT_STATUS_OK;
			}
			break;
		default:	/* Other ACE types not handled/supported */
			break;
		}
	}

done:
	if (bits_remaining != 0) {
		return NT_STATUS_ACCESS_DENIED;
	}

	return NT_STATUS_OK;
}