Use AccessCheck for current user effective file permissions

On Windows, QFileInfo.isWritable() was returning true in situations
where the file would only be writable with elevated privileges. Using
AccessCheck instead of GetEffectiveRightsFromAcl to get the correct
results.

Done-with: Friedemann Kleint <Friedemann.Kleint@qt.io>
Done-with: Edward Welbourne <edward.welbourne@qt.io>
Task-number: QTBUG-30148
Change-Id: I7a3468ac069bf782ca312078e3a84107b6cd468c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 55 insertions, 9 deletions

diff --git a/src/corelib/io/qfilesystemengine_win.cpp b/src/corelib/io/qfilesystemengine_win.cpp
index b01aa55756..c9a56a81cc 100644..100755
--- a/src/corelib/io/qfilesystemengine_win.cpp
+++ b/src/corelib/io/qfilesystemengine_win.cpp
@@ -178,6 +178,7 @@ static TRUSTEE_W currentUserTrusteeW;
 static TRUSTEE_W worldTrusteeW;
 static PSID currentUserSID = 0;
 static PSID worldSID = 0;
+static HANDLE currentUserImpersonatedToken = nullptr;
 
 /*
     Deletes the allocated SIDs during global static cleanup
@@ -198,6 +199,11 @@ SidCleanup::~SidCleanup()
         ::FreeSid(worldSID);
         worldSID = 0;
     }
+
+    if (currentUserImpersonatedToken) {
+        ::CloseHandle(currentUserImpersonatedToken);
+        currentUserImpersonatedToken = nullptr;
+    }
 }
 
 Q_GLOBAL_STATIC(SidCleanup, initSidCleanup)
@@ -254,6 +260,12 @@ static void resolveLibs()
                 ::CloseHandle(token);
             }
 
+            token = nullptr;
+            if (::OpenProcessToken(hnd, TOKEN_IMPERSONATE | TOKEN_QUERY | TOKEN_DUPLICATE | STANDARD_RIGHTS_READ, &token)) {
+                ::DuplicateToken(token, SecurityImpersonation, &currentUserImpersonatedToken);
+                ::CloseHandle(token);
+            }
+
             typedef BOOL (WINAPI *PtrAllocateAndInitializeSid)(PSID_IDENTIFIER_AUTHORITY, BYTE, DWORD, DWORD, DWORD, DWORD, DWORD, DWORD, DWORD, DWORD, PSID*);
             PtrAllocateAndInitializeSid ptrAllocateAndInitializeSid = (PtrAllocateAndInitializeSid)GetProcAddress(advapiHnd, "AllocateAndInitializeSid");
             if (ptrAllocateAndInitializeSid) {
@@ -721,15 +733,49 @@ bool QFileSystemEngine::fillPermissions(const QFileSystemEntry &entry, QFileSyst
                 ACCESS_MASK access_mask;
                 TRUSTEE_W trustee;
                 if (what & QFileSystemMetaData::UserPermissions) { // user
-                    data.knownFlagsMask |= QFileSystemMetaData::UserPermissions;
-                    if(ptrGetEffectiveRightsFromAclW(pDacl, &currentUserTrusteeW, &access_mask) != ERROR_SUCCESS)
-                        access_mask = (ACCESS_MASK)-1;
-                    if(access_mask & ReadMask)
-                        data.entryFlags |= QFileSystemMetaData::UserReadPermission;
-                    if(access_mask & WriteMask)
-                        data.entryFlags|= QFileSystemMetaData::UserWritePermission;
-                    if(access_mask & ExecMask)
-                        data.entryFlags|= QFileSystemMetaData::UserExecutePermission;
+                    // Using AccessCheck because GetEffectiveRightsFromAcl doesn't account for elevation
+                    if (currentUserImpersonatedToken) {
+                        GENERIC_MAPPING mapping = {FILE_GENERIC_READ, FILE_GENERIC_WRITE, FILE_GENERIC_EXECUTE, FILE_ALL_ACCESS};
+                        PRIVILEGE_SET privileges;
+                        DWORD grantedAccess;
+                        BOOL result;
+
+                        data.knownFlagsMask |= QFileSystemMetaData::UserPermissions;
+                        DWORD genericAccessRights = GENERIC_READ;
+                        ::MapGenericMask(&genericAccessRights, &mapping);
+
+                        DWORD privilegesLength = sizeof(privileges);
+                        if (::AccessCheck(pSD, currentUserImpersonatedToken, genericAccessRights,
+                                          &mapping, &privileges, &privilegesLength, &grantedAccess, &result) && result) {
+                            data.entryFlags |= QFileSystemMetaData::UserReadPermission;
+                        }
+
+                        privilegesLength = sizeof(privileges);
+                        genericAccessRights = GENERIC_WRITE;
+                        ::MapGenericMask(&genericAccessRights, &mapping);
+                        if (::AccessCheck(pSD, currentUserImpersonatedToken, genericAccessRights,
+                                          &mapping, &privileges, &privilegesLength, &grantedAccess, &result) && result) {
+                            data.entryFlags |= QFileSystemMetaData::UserWritePermission;
+                        }
+
+                        privilegesLength = sizeof(privileges);
+                        genericAccessRights = GENERIC_EXECUTE;
+                        ::MapGenericMask(&genericAccessRights, &mapping);
+                        if (::AccessCheck(pSD, currentUserImpersonatedToken, genericAccessRights,
+                                          &mapping, &privileges, &privilegesLength, &grantedAccess, &result) && result) {
+                            data.entryFlags |= QFileSystemMetaData::UserExecutePermission;
+                        }
+                    } else { // fallback to GetEffectiveRightsFromAcl
+                        data.knownFlagsMask |= QFileSystemMetaData::UserPermissions;
+                        if (ptrGetEffectiveRightsFromAclW(pDacl, &currentUserTrusteeW, &access_mask) != ERROR_SUCCESS)
+                            access_mask = ACCESS_MASK(-1);
+                        if (access_mask & ReadMask)
+                            data.entryFlags |= QFileSystemMetaData::UserReadPermission;
+                        if (access_mask & WriteMask)
+                            data.entryFlags|= QFileSystemMetaData::UserWritePermission;
+                        if (access_mask & ExecMask)
+                            data.entryFlags|= QFileSystemMetaData::UserExecutePermission;
+                    }
                 }
                 if (what & QFileSystemMetaData::OwnerPermissions) { // owner
                     data.knownFlagsMask |= QFileSystemMetaData::OwnerPermissions;