access_check.c

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/*
   Unix SMB/CIFS implementation.

   security access checking routines

   Copyright (C) Andrew Tridgell 2004

   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"


/*
  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 | SEC_STD_DELETE;
	} else if (security_token_has_privilege(token, SEC_PRIV_RESTORE)) {
		granted |= SEC_STD_DELETE;
	}

	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. 
*/
NTSTATUS sec_access_check(const struct security_descriptor *sd, 
			  const struct security_token *token,
			  uint32_t access_desired,
			  uint32_t *access_granted)
{
	int i;
	uint32_t bits_remaining;

	*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 & ~SEC_STD_DELETE;
	}

	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;
		}
	}

	/* dacl not present allows access */
	if (!(sd->type & SEC_DESC_DACL_PRESENT)) {
		*access_granted = access_desired;
		return NT_STATUS_OK;
	}

	/* empty dacl denies access */
	if (sd->dacl == NULL || sd->dacl->num_aces == 0) {
		return NT_STATUS_ACCESS_DENIED;
	}

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

	/* 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;
		}

		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:
			if (bits_remaining & ace->access_mask) {
				return NT_STATUS_ACCESS_DENIED;
			}
			break;
		default:	/* Other ACE types not handled/supported */
			break;
		}
	}

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

	return NT_STATUS_OK;
}