PKCS#11中的内存所有权C_FindObjects其中ulMaxObjectCount!= 1

Question

当API返回可变长度的项列表时,PKCS#11 v2.40的作者使用通用模式.在诸如C_GetSlotList和的API中C_GetMechanismList,应用程序应该两次调用API.在第一次调用中,指向a的指针CK_ULONG设置为下次调用时将返回的项目数.这允许应用程序分配足够的内存并再次调用API以检索结果.

该C_FindObjects调用还返回可变数量的项,但它使用不同的范例.该参数CK_OBJECT_HANDLE_PTR phObject设置为结果列表的头部.该参数CK_ULONG_PTR pulObjectCount设置为返回的项目数,确保小于CK_ULONG ulMaxObjectCount.

该标准没有明确说明phObject必须是一个有效的指针,指向足够容纳ulMaxObjectCount CK_OBJECT_HANDLEs 的内存块.

可以将标准解释为应用程序必须悲观地为ulMaxObjectCount对象分配足够的内存.或者,可以将标准解释为PKCS#11实现将分配pulObjectCount CK_OBJECT_HANDLEs,然后应用程序负责释放该内存.然而,后来的解释似乎是可疑的,因为标准中没有其他地方PKCS#11的实现曾经分配内存.

该段落是:

C_FindObjects continues a search for token and session objects that 
match a template, obtaining additional object handles. hSession is 
the session’s handle; phObject points to the location that receives 
the list (array) of additional object handles; ulMaxObjectCount is 
the maximum number of object handles to be returned; pulObjectCount 
points to the location that receives the actual number of object 
handles returned.

If there are no more objects matching the template, then the location 
that pulObjectCount points to receives the value 0.

The search MUST have been initialized with C_FindObjectsInit.

非规范性示例不是很有用,因为它设置ulMaxObjectCount为1.但是,它确实为该一个条目分配内存.这似乎表明应用程序必须悲观地预先分配内存.

CK_SESSION_HANDLE hSession;
CK_OBJECT_HANDLE hObject;
CK_ULONG ulObjectCount;
CK_RV rv;
.
.
rv = C_FindObjectsInit(hSession, NULL_PTR, 0);
assert(rv == CKR_OK);
while (1) {
 rv = C_FindObjects(hSession, &hObject, 1, &ulObjectCount);
 if (rv != CKR_OK || ulObjectCount == 0)
 break;
 .
 .
}
rv = C_FindObjectsFinal(hSession);
assert(rv == CKR_OK);

规范链接:http://docs.oasis-open.org/pkcs11/pkcs11-base/v2.40/pkcs11-base-v2.40.pdf

Answer 1

是的,似乎应用程序负责为返回的对象句柄分配空间C_FindObjects().示例代码执行此操作,即使它一次只请求一个对象句柄,所以您应该这样做.

你也可以重写示例代码来请求多个对象句柄,例如:

#define MAX_OBJECT_COUNT 100  /* arbitrary value */

K_SESSION_HANDLE hSession;
CK_OBJECT_HANDLE hObjects[MAX_OBJECT_COUNT];
CK_ULONG ulObjectCount, i;
CK_RV rv;

rv = C_FindObjectsInit(hSession, NULL_PTR, 0);
assert(rv == CKR_OK);
while (1) {
  rv = C_FindObjects(hSession, hObjects, MAX_OBJECT_COUNT, &ulObjectCount);
  if (rv != CKR_OK || ulObjectCount == 0) break;
  for (i = 0; i < ulObjectCount; i++) {
    /* do something with hObjects[i] here */
  }
}
rv = C_FindObjectsFinal(hSession);
assert(rv == CKR_OK);

据推测,在单个C_FindObjects()调用中请求多个对象句柄的能力旨在作为性能优化.

FWIW,这几乎就是有多少C标准库函数fread().使用一个字节从文件读取数据是非常低效的fgetc(),因此该fread()函数允许您分配一个任意大的缓冲区并读取适合它的数据.