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8bb672aa4d
Current group membership resolution though very effective, is very slow. In a typical domain joined enterprise machine, adding a simple entry like the following in sshd_config AllowGroups administrators will incur a long delay in remote session establishment as sshd tried to pull all groups associated with the domain user. Changes in this PR optimize the general case scenarios where no wild cards are in use. Specifically rules like this are processed promptly: AllowGroups group1, group2, group3 //with no wild cards Match Group group1 //single group with no negation and wild cards Optimization is done by resolve the groupname in rule immediately to SID and checking its membership against user token. Enumerating the entire group membership is done on a lazy on-demand basis. Beyond the optimization, there are 2 functional changes - removed domain prefix for builtin groups - removed domain prefix'ed versions of local groups since we are strictly following the convention that local principals shouldn't have any domain qualification.
143 lines
4.9 KiB
C
143 lines
4.9 KiB
C
/*
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* Author: Yanbing Wang <yawang@microsoft.com>
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*
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* Support file permission check on Win32 based operating systems.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <Windows.h>
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#include <Sddl.h>
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#include <Aclapi.h>
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#include <lm.h>
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#include <stdio.h>
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#include "inc\pwd.h"
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#include "sshfileperm.h"
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#include "debug.h"
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#include "misc_internal.h"
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#include "config.h"
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/*
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* The function is to check if current user is secure to access to the file.
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* Check the owner of the file is one of these types: Local Administrators groups, system account, current user account
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* Check the users have access permission to the file don't voilate the following rules:
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1. no user other than local administrators group, system account, and pwd user have write permission on the file
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2. sshd account can only have read permission
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* Returns 0 on success and -1 on failure
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*/
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int
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check_secure_file_permission(const char *input_path, struct passwd * pw)
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{
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PSECURITY_DESCRIPTOR pSD = NULL;
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wchar_t * path_utf16 = NULL;
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PSID owner_sid = NULL, user_sid = NULL;
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PACL dacl = NULL;
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DWORD error_code = ERROR_SUCCESS;
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BOOL is_valid_sid = FALSE, is_valid_acl = FALSE;
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char *bad_user = NULL;
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int ret = 0;
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if ((user_sid = get_sid(pw ? pw->pw_name : NULL)) == NULL)
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goto cleanup;
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if ((path_utf16 = resolved_path_utf16(input_path)) == NULL) {
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ret = -1;
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goto cleanup;
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}
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/*Get the owner sid of the file.*/
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if ((error_code = GetNamedSecurityInfoW(path_utf16, SE_FILE_OBJECT,
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OWNER_SECURITY_INFORMATION | DACL_SECURITY_INFORMATION,
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&owner_sid, NULL, &dacl, NULL, &pSD)) != ERROR_SUCCESS) {
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debug3("failed to retrieve the owner sid and dacl of file %S with error code: %d", path_utf16, error_code);
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errno = EOTHER;
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ret = -1;
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goto cleanup;
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}
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if (((is_valid_sid = IsValidSid(owner_sid)) == FALSE) || ((is_valid_acl = IsValidAcl(dacl)) == FALSE)) {
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debug3("IsValidSid: %d; is_valid_acl: %d", is_valid_sid, is_valid_acl);
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ret = -1;
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goto cleanup;
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}
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if (!IsWellKnownSid(owner_sid, WinBuiltinAdministratorsSid) &&
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!IsWellKnownSid(owner_sid, WinLocalSystemSid) &&
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!EqualSid(owner_sid, user_sid)) {
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debug3("Bad owner on %S", path_utf16);
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ret = -1;
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goto cleanup;
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}
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/*
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iterate all aces of the file to find out if there is voilation of the following rules:
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1. no others than administrators group, system account, and current user account have write permission on the file
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2. sshd account can only have read permission
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*/
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for (DWORD i = 0; i < dacl->AceCount; i++) {
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PVOID current_ace = NULL;
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PACE_HEADER current_aceHeader = NULL;
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PSID current_trustee_sid = NULL;
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ACCESS_MASK current_access_mask = 0;
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if (!GetAce(dacl, i, ¤t_ace)) {
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debug3("GetAce() failed");
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errno = EOTHER;
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ret = -1;
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goto cleanup;
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}
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current_aceHeader = (PACE_HEADER)current_ace;
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/* only interested in Allow ACE */
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if(current_aceHeader->AceType != ACCESS_ALLOWED_ACE_TYPE)
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continue;
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PACCESS_ALLOWED_ACE pAllowedAce = (PACCESS_ALLOWED_ACE)current_ace;
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current_trustee_sid = &(pAllowedAce->SidStart);
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current_access_mask = pAllowedAce->Mask;
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/*no need to check administrators group, pwd user account, and system account*/
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if (IsWellKnownSid(current_trustee_sid, WinBuiltinAdministratorsSid) ||
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IsWellKnownSid(current_trustee_sid, WinLocalSystemSid) ||
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EqualSid(current_trustee_sid, user_sid)) {
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continue;
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} else {
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ret = -1;
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if (ConvertSidToStringSid(current_trustee_sid, &bad_user) == FALSE) {
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debug3("ConvertSidToSidString failed with %d. ", GetLastError());
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break;
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}
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debug3("Bad permissions. Try removing permissions for user: %s on file %S.", bad_user, path_utf16);
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break;
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}
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}
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cleanup:
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if(bad_user)
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LocalFree(bad_user);
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if (pSD)
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LocalFree(pSD);
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if (user_sid)
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free(user_sid);
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if(path_utf16)
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free(path_utf16);
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return ret;
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}
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