问：我在服务器上用 CreateFileMapping 创建了一段共享内存。让这个exe始终在服务器上跑。
同时，别的用户在客户端用IE访问服务器，将要查询的数据通过C#制作的网页提交上来，服务器得到网页参数后，建立一个COM对象访问上一个exe的共享内存，然后将在共享内存中的查询结果返回给客户。
问题是现在这个COM无法用openmapping访问exe的共享内存，提示 访问拒绝 。而我在服务器上随便建议一个工程编译成exe,文件就可访问这段共享内存!!为何在网页中就不成？COM难道要有什么 权限 设置.两个进程之间的权限整合方法是什么？怎么用DACL?
我用ATL写了一个Service,在这个Service中，我创建了一块共享内存(Memory Mapping)和一个Mutex
然后我在另一个普通程序中去访问这块共享内存和Mutex,但是，我用CreateMutex打开Mutex失败，GetLastError()返回5，含义是访问被拒绝！！
同样，我在用MapViewOfFile时，也得到同样的错误！！！！！！
我已经知道原因是因为在创建共享内存和Mutext时，SECURITY_ATTRIBUTES我设为NULL!!!
但是我没有解决的方法,希望各位大虾帮帮忙！
答：检查服务运行所使用的用户的权限。通常，为了安全起见，服务进程的拥有者权限是很低的。为了让服务进程访问对象，你需要在创建共享内存时指定一个更加广泛的的安全描述符，增加一个新的访问控制项目(ACE)给你的ASP进程的拥有者。默认的访问控制列表(ACL)只包含创建者和管理员组。
下列代码创建一个所有用户都可以访问的安全描述符。你可以在创建共享内存时使用这个安全描述符。
CShareRestrictedSD ShareRestrictedSD;
hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE, // Current file handle.
ShareRestrictedSD.GetSA(), // Default security.
// NULL,
PAGE_READWRITE, // Read/write permission.
0, // Max. object size.
FileSize, // Size of hFile.
MapName); // Name of mapping object.
class CShareRestrictedSD
{
public:
CShareRestrictedSD();
virtual ~CShareRestrictedSD();
SECURITY_ATTRIBUTES* GetSA();
protected:
PVOID ptr;
SECURITY_ATTRIBUTES sa;
SECURITY_DESCRIPTOR sd;
};
//如果这家伙起作用，那么它的作者是jiangsheng；
//如果这家伙一点用没有，那我不知道它的作者。
PVOID BuildRestrictedSD(PSECURITY_DESCRIPTOR pSD) {
DWORD dwAclLength;
PSID psidEveryone = NULL;
PACL pDACL = NULL;
BOOL bResult = FALSE;
PACCESS_ALLOWED_ACE pACE = NULL;
SID_IDENTIFIER_AUTHORITY siaWorld = SECURITY_WORLD_SID_AUTHORITY ;
SECURITY_INFORMATION si = DACL_SECURITY_INFORMATION;
__try {
// initialize the security descriptor
if (!InitializeSecurityDescriptor(pSD,
SECURITY_DESCRIPTOR_REVISION)) {
printf("InitializeSecurityDescriptor() failed with error %d\n",
GetLastError());
__leave;
}
// obtain a sid for the Authenticated Users Group
if (!AllocateAndInitializeSid(&siaWorld, 1,
SECURITY_WORLD_RID, 0, 0, 0, 0, 0, 0, 0,
&psidEveryone)) {
printf("AllocateAndInitializeSid() failed with error %d\n",
GetLastError());
__leave;
}
// NOTE:
//
// The Authenticated Users group includes all user accounts that
// have been successfully authenticated by the system. If access
// must be restricted to a specific user or group other than
// Authenticated Users, the SID can be constructed using the
// LookupAccountSid() API based on a user or group name.
// calculate the DACL length
dwAclLength = sizeof(ACL)
// add space for Authenticated Users group ACE
+ sizeof(ACCESS_ALLOWED_ACE) - sizeof(DWORD)
+ GetLengthSid(psidEveryone);
// allocate memory for the DACL
pDACL = (PACL) HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY,
dwAclLength);
if (!pDACL) {
printf("HeapAlloc() failed with error %d\n", GetLastError());
__leave;
}
// initialize the DACL
if (!InitializeAcl(pDACL, dwAclLength, ACL_REVISION)) {
printf("InitializeAcl() failed with error %d\n",
GetLastError());
__leave;
}
// add the Authenticated Users group ACE to the DACL with
// GENERIC_READ, GENERIC_WRITE, and GENERIC_EXECUTE access
if (!AddAccessAllowedAce(pDACL, ACL_REVISION,
GENERIC_ALL,
psidEveryone)) {
printf("AddAccessAllowedAce() failed with error %d\n",
GetLastError());
__leave;
}
// set the DACL in the security descriptor
if (!SetSecurityDescriptorDacl(pSD, TRUE, pDACL, FALSE)) {
printf("SetSecurityDescriptorDacl() failed with error %d\n",
GetLastError());
__leave;
}
bResult = TRUE;
} __finally {
if (psidEveryone) FreeSid(psidEveryone);
}
if (bResult == FALSE) {
if (pDACL) HeapFree(GetProcessHeap(), 0, pDACL);
pDACL = NULL;
}
return (PVOID) pDACL;
}
// The following function frees memory allocated in the
// BuildRestrictedSD() function
VOID FreeRestrictedSD(PVOID ptr) {
if (ptr) HeapFree(GetProcessHeap(), 0, ptr);
return;
}
CShareRestrictedSD::CShareRestrictedSD()
{
ptr=NULL;
sa.nLength = sizeof(sa);
sa.lpSecurityDescriptor = &sd;
sa.bInheritHandle = FALSE;
// build a restricted security descriptor
ptr = BuildRestrictedSD(&sd);
if (!ptr) {
TRACE("BuildRestrictedSD() failed\n");
}
}
CShareRestrictedSD::~CShareRestrictedSD()
{
if(ptr){
FreeRestrictedSD(ptr);
}
}
SECURITY_ATTRIBUTES* CShareRestrictedSD::GetSA()
{
if(ptr){
return &sa;
}
else
return NULL;
}
更多信息可以参考
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