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/usr/include/linux/capability.h#defines中的文件定义了 34 种可能的功能。它是这样的：

#define CAP_CHOWN            0

#define CAP_DAC_OVERRIDE     1

.....

#define CAP_MAC_ADMIN        33

#define CAP_LAST_CAP         CAP_MAC_ADMIN

每个进程都有这样定义的能力

typedef struct __user_cap_data_struct {

        __u32 effective;
        __u32 permitted;
        __u32 inheritable;
} * cap_user_data_t;

我很困惑——一个进程可以有 32 位的有效能力，但在capability.h 中定义的能力总量是 34。如何在 32 位掩码中编码 34 个位置？

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2 回答 2

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因为您还没有阅读所有手册。

capget 手册首先说服您不要使用它：

These two functions are the raw kernel interface for getting  and  set‐
ting  thread capabilities.  Not only are these system calls specific to
Linux, but the kernel API is likely to change and use  of  these  func‐
tions  (in  particular the format of the cap_user_*_t types) is subject
to extension with each kernel revision,  but  old  programs  will  keep
working.

The  portable  interfaces  are  cap_set_proc(3) and cap_get_proc(3); if
possible you should use those interfaces in applications.  If you  wish
to use the Linux extensions in applications, you should use the easier-
to-use interfaces capsetp(3) and capgetp(3).

当前详细信息

Now that you have been warned, some current kernel details.  The struc‐
tures are defined as follows.

#define _LINUX_CAPABILITY_VERSION_1  0x19980330
#define _LINUX_CAPABILITY_U32S_1     1

#define _LINUX_CAPABILITY_VERSION_2  0x20071026
#define _LINUX_CAPABILITY_U32S_2     2

[...]
effective,  permitted,  inheritable  are  bitmasks  of the capabilities
defined in capability(7).  Note the CAP_* values are  bit  indexes  and
need to be bit-shifted before ORing into the bit fields.
[...]
Kernels  prior  to  2.6.25  prefer  32-bit  capabilities  with  version
_LINUX_CAPABILITY_VERSION_1, and kernels 2.6.25+ prefer 64-bit capabil‐
ities with version _LINUX_CAPABILITY_VERSION_2.  Note, 64-bit capabili‐
ties  use  datap[0]  and datap[1], whereas 32-bit capabilities only use
datap[0].

wheredatap前面定义为指向 a 的指针__user_cap_data_struct。因此，您只需在两个__u32数组中表示一个 64 位值__user_cap_data_struct。

仅此一项就告诉我永远不要使用此 API，因此我没有阅读手册的其余部分。

于 2011-12-27T20:51:33.590 回答
2

它们不是位掩码，它们只是常量。EGCAP_MAC_ADMIN设置多于一位。在二进制中，33 是什么，10001？

于 2011-12-27T18:49:30.827 回答