1CAPGET(2) Linux Programmer's Manual CAPGET(2)
2
6 capget, capset - set/get capabilities of thread(s)
7
9 #include <linux/capability.h> /* Definition of CAP_* and
10 _LINUX_CAPABILITY_* constants */
11 #include <sys/syscall.h> /* Definition of SYS_* constants */
12 #include <unistd.h>
13 int syscall(SYS_capget, cap_user_header_t hdrp,
15 cap_user_data_t datap);
16 int syscall(SYS_capset, cap_user_header_t hdrp,
17 const cap_user_data_t datap);
18 Note: glibc provides no wrappers for these system calls, necessitating
20 the use of syscall(2).
21
23 These two system calls are the raw kernel interface for getting and
24 setting thread capabilities. Not only are these system calls specific
25 to Linux, but the kernel API is likely to change and use of these sys‐
26 tem calls (in particular the format of the cap_user_*_t types) is sub‐
27 ject to extension with each kernel revision, but old programs will keep
28 working.
29 The portable interfaces are cap_set_proc(3) and cap_get_proc(3); if
31 possible, you should use those interfaces in applications; see NOTES.
32 Current details
34 Now that you have been warned, some current kernel details. The struc‐
35 tures are defined as follows.
36 #define _LINUX_CAPABILITY_VERSION_1 0x19980330
38 #define _LINUX_CAPABILITY_U32S_1 1
39 /* V2 added in Linux 2.6.25; deprecated */
41 #define _LINUX_CAPABILITY_VERSION_2 0x20071026
42 #define _LINUX_CAPABILITY_U32S_2 2
43 /* V3 added in Linux 2.6.26 */
45 #define _LINUX_CAPABILITY_VERSION_3 0x20080522
46 #define _LINUX_CAPABILITY_U32S_3 2
47 typedef struct __user_cap_header_struct {
49 __u32 version;
50 int pid;
51 } *cap_user_header_t;
52 typedef struct __user_cap_data_struct {
54 __u32 effective;
55 __u32 permitted;
56 __u32 inheritable;
57 } *cap_user_data_t;
58 The effective, permitted, and inheritable fields are bit masks of the
60 capabilities defined in capabilities(7). Note that the CAP_* values
61 are bit indexes and need to be bit-shifted before ORing into the bit
62 fields. To define the structures for passing to the system call, you
63 have to use the struct __user_cap_header_struct and struct
64 __user_cap_data_struct names because the typedefs are only pointers.
65 Kernels prior to 2.6.25 prefer 32-bit capabilities with version
67 _LINUX_CAPABILITY_VERSION_1. Linux 2.6.25 added 64-bit capability
68 sets, with version _LINUX_CAPABILITY_VERSION_2. There was, however, an
69 API glitch, and Linux 2.6.26 added _LINUX_CAPABILITY_VERSION_3 to fix
70 the problem.
71 Note that 64-bit capabilities use datap[0] and datap[1], whereas 32-bit
73 capabilities use only datap[0].
74 On kernels that support file capabilities (VFS capabilities support),
76 these system calls behave slightly differently. This support was added
77 as an option in Linux 2.6.24, and became fixed (nonoptional) in Linux
78 2.6.33.
79 For capget() calls, one can probe the capabilities of any process by
81 specifying its process ID with the hdrp->pid field value.
82 For details on the data, see capabilities(7).
84 With VFS capabilities support
86 VFS capabilities employ a file extended attribute (see xattr(7)) to al‐
87 low capabilities to be attached to executables. This privilege model
88 obsoletes kernel support for one process asynchronously setting the ca‐
89 pabilities of another. That is, on kernels that have VFS capabilities
90 support, when calling capset(), the only permitted values for hdrp->pid
91 are 0 or, equivalently, the value returned by gettid(2).
92 Without VFS capabilities support
94 On older kernels that do not provide VFS capabilities support capset()
95 can, if the caller has the CAP_SETPCAP capability, be used to change
96 not only the caller's own capabilities, but also the capabilities of
97 other threads. The call operates on the capabilities of the thread
98 specified by the pid field of hdrp when that is nonzero, or on the ca‐
99 pabilities of the calling thread if pid is 0. If pid refers to a sin‐
100 gle-threaded process, then pid can be specified as a traditional
101 process ID; operating on a thread of a multithreaded process requires a
102 thread ID of the type returned by gettid(2). For capset(), pid can
103 also be: -1, meaning perform the change on all threads except the
104 caller and init(1); or a value less than -1, in which case the change
105 is applied to all members of the process group whose ID is -pid.
106
108 On success, zero is returned. On error, -1 is returned, and errno is
109 set to indicate the error.
110 The calls fail with the error EINVAL, and set the version field of hdrp
112 to the kernel preferred value of _LINUX_CAPABILITY_VERSION_? when an
113 unsupported version value is specified. In this way, one can probe
114 what the current preferred capability revision is.
115
117 EFAULT Bad memory address. hdrp must not be NULL. datap may be NULL
118 only when the user is trying to determine the preferred capabil‐
119 ity version format supported by the kernel.
120 EINVAL One of the arguments was invalid.
122 EPERM An attempt was made to add a capability to the permitted set, or
124 to set a capability in the effective set that is not in the per‐
125 mitted set.
126 EPERM An attempt was made to add a capability to the inheritable set,
128 and either:
129 * that capability was not in the caller's bounding set; or
131 * the capability was not in the caller's permitted set and the
133 caller lacked the CAP_SETPCAP capability in its effective
134 set.
135 EPERM The caller attempted to use capset() to modify the capabilities
137 of a thread other than itself, but lacked sufficient privilege.
138 For kernels supporting VFS capabilities, this is never permit‐
139 ted. For kernels lacking VFS support, the CAP_SETPCAP capabil‐
140 ity is required. (A bug in kernels before 2.6.11 meant that
141 this error could also occur if a thread without this capability
142 tried to change its own capabilities by specifying the pid field
143 as a nonzero value (i.e., the value returned by getpid(2)) in‐
144 stead of 0.)
145 ESRCH No such thread.
147
149 These system calls are Linux-specific.
150
152 The portable interface to the capability querying and setting functions
153 is provided by the libcap library and is available here:
154 ⟨http://git.kernel.org/cgit/linux/kernel/git/morgan/libcap.git⟩
155
157 clone(2), gettid(2), capabilities(7)
158
160 This page is part of release 5.13 of the Linux man-pages project. A
161 description of the project, information about reporting bugs, and the
162 latest version of this page, can be found at
163 https://www.kernel.org/doc/man-pages/.
164Linux 2021-03-22 CAPGET(2)