.\" written by Andrew Morgan <morgan@kernel.org>
+.\"
+.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
.\" may be distributed as per GPL
+.\" %%%LICENSE_END
+.\"
.\" Modified by David A. Wheeler <dwheeler@ida.org>
.\" Modified 2004-05-27, mtk
.\" Modified 2004-06-21, aeb
.\" 64-bit capability sets in kernel 2.6.2[45].
.\" Modified 2009-01-26, andi kleen
.\"
-.TH CAPGET 2 2010-09-20 "Linux" "Linux Programmer's Manual"
+.TH CAPGET 2 2019-03-06 "Linux" "Linux Programmer's Manual"
.SH NAME
capget, capset \- set/get capabilities of thread(s)
.SH SYNOPSIS
.B #include <sys/capability.h>
-.sp
+.PP
.BI "int capget(cap_user_header_t " hdrp ", cap_user_data_t " datap );
-.sp
+.PP
.BI "int capset(cap_user_header_t " hdrp ", const cap_user_data_t " datap );
.SH DESCRIPTION
-As of Linux 2.2,
-the power of the superuser (root) has been partitioned into
-a set of discrete capabilities.
-Each thread has a set of effective capabilities identifying
-which capabilities (if any) it may currently exercise.
-Each thread also has a set of inheritable capabilities that may be
-passed through an
-.BR execve (2)
-call, and a set of permitted capabilities
-that it can make effective or inheritable.
-.PP
-These two functions are the raw kernel interface for getting and
+These two system calls are the raw kernel interface for getting and
setting thread capabilities.
Not only are these system calls specific to Linux,
but the kernel API is likely to change and use of
-these functions (in particular the format of the
+these system calls (in particular the format of the
.I cap_user_*_t
types) is subject to extension with each kernel revision,
but old programs will keep working.
-.sp
+.PP
The portable interfaces are
.BR cap_set_proc (3)
and
.BR 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
-.BR capsetp (3)
-and
-.BR capgetp (3).
-.SS "Current details"
+if possible, you should use those interfaces in applications.
+.\"
+.SS Current details
Now that you have been warned, some current kernel details.
The structures are defined as follows.
-.sp
-.nf
+.PP
.in +4n
+.EX
#define _LINUX_CAPABILITY_VERSION_1 0x19980330
#define _LINUX_CAPABILITY_U32S_1 1
+ /* V2 added in Linux 2.6.25; deprecated */
#define _LINUX_CAPABILITY_VERSION_2 0x20071026
+.\" commit e338d263a76af78fe8f38a72131188b58fceb591
+.\" Added 64 bit capability support
#define _LINUX_CAPABILITY_U32S_2 2
+ /* V3 added in Linux 2.6.26 */
+#define _LINUX_CAPABILITY_VERSION_3 0x20080522
+.\" commit ca05a99a54db1db5bca72eccb5866d2a86f8517f
+#define _LINUX_CAPABILITY_U32S_3 2
+
typedef struct __user_cap_header_struct {
__u32 version;
int pid;
__u32 permitted;
__u32 inheritable;
} *cap_user_data_t;
-.fi
-.in -4n
-.sp
-.I effective, permitted, inheritable
-are bitmasks of the capabilities defined in
-.I capability(7).
-Note the
-.I CAP_*
+.EE
+.in
+.PP
+The
+.IR effective ,
+.IR permitted ,
+and
+.I inheritable
+fields are bit masks of the capabilities defined in
+.BR capabilities (7).
+Note that the
+.B CAP_*
values are bit indexes and need to be bit-shifted before ORing into
the bit fields.
-To define the structures for passing to the system call you have to use the
+To define the structures for passing to the system call, you have to use the
.I struct __user_cap_header_struct
and
.I struct __user_cap_data_struct
names because the typedefs are only pointers.
-
+.PP
Kernels prior to 2.6.25 prefer
32-bit capabilities with version
-.BR _LINUX_CAPABILITY_VERSION_1 ,
-and kernels 2.6.25+ prefer 64-bit capabilities with version
+.BR _LINUX_CAPABILITY_VERSION_1 .
+Linux 2.6.25 added 64-bit capability sets, with version
.BR _LINUX_CAPABILITY_VERSION_2 .
-Note, 64-bit capabilities use
+There was, however, an API glitch, and Linux 2.6.26 added
+.BR _LINUX_CAPABILITY_VERSION_3
+to fix the problem.
+.PP
+Note that 64-bit capabilities use
.IR datap [0]
and
.IR datap [1],
-whereas 32-bit capabilities only use
+whereas 32-bit capabilities use only
.IR datap [0].
-.sp
-Another change affecting the behavior of these system calls is kernel
-support for file capabilities (VFS capability support).
-This support is currently a compile time option (added in kernel 2.6.24).
-.sp
+.PP
+On kernels that support file capabilities (VFS capabilities support),
+these system calls behave slightly differently.
+This support was added as an option in Linux 2.6.24,
+and became fixed (nonoptional) in Linux 2.6.33.
+.PP
For
.BR capget ()
calls, one can probe the capabilities of any process by specifying its
process ID with the
.I hdrp->pid
field value.
-.SS With VFS Capability Support
-VFS Capability support creates a file-attribute method for adding
-capabilities to privileged executables.
+.PP
+For details on the data, see
+.BR capabilities (7).
+.\"
+.SS With VFS capabilities support
+VFS capabilities employ a file extended attribute (see
+.BR xattr (7))
+to allow capabilities to be attached to executables.
This privilege model obsoletes kernel support for one process
asynchronously setting the capabilities of another.
-That is, with VFS support, for
-.BR capset ()
-calls the only permitted values for
+That is, on kernels that have VFS capabilities support, when calling
+.BR capset (),
+the only permitted values for
.I hdrp->pid
-are 0 or
-.BR getpid (2),
-which are equivalent.
-.SS Without VFS Capability Support
-When the kernel does not support VFS capabilities,
+are 0 or, equivalently, the value returned by
+.BR gettid (2).
+.\"
+.SS Without VFS capabilities support
+On older kernels that do not provide VFS capabilities support
.BR capset ()
-calls can operate on the capabilities of the thread specified by the
+can, if the caller has the
+.BR CAP_SETPCAP
+capability, be used to change not only the caller's own capabilities,
+but also the capabilities of other threads.
+The call operates on the capabilities of the thread specified by the
.I pid
field of
.I hdrp
.I pid
can also be: \-1, meaning perform the change on all threads except the
caller and
-.BR init (8);
+.BR init (1);
or a value less than \-1, in which case the change is applied
to all members of the process group whose ID is \-\fIpid\fP.
-
-For details on the data, see
-.BR capabilities (7).
-.SH "RETURN VALUE"
+.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
-
-The calls will fail with the error
+.PP
+The calls fail with the error
.BR EINVAL ,
and set the
.I version
.I hdrp
must not be NULL.
.I datap
-may only be NULL when the user is trying to determine the preferred
+may be NULL only when the user is trying to determine the preferred
capability version format supported by the kernel.
.TP
.B EINVAL
.TP
.B ESRCH
No such thread.
-.SH "CONFORMING TO"
+.SH CONFORMING TO
These system calls are Linux-specific.
.SH NOTES
The portable interface to the capability querying and setting
.I libcap
library and is available here:
.br
-http://www.kernel.org/pub/linux/libs/security/linux-privs
-.SH "SEE ALSO"
+.UR http://git.kernel.org/cgit\:/linux\:/kernel\:/git\:/morgan\:\:/libcap.git
+.UE
+.SH SEE ALSO
.BR clone (2),
.BR gettid (2),
.BR capabilities (7)
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