NAME
capget, capset - set/get capabilities
SYNOPSIS
#undef _POSIX_SOURCE
#include <sys/capability.h>
I int capget(cap_user_header_t hdrp , cap_user_data_t datap );
I int capset(cap_user_header_t hdrp , const cap_user_data_t datap );
DESCRIPTION
As of Linux 2.2, the power of the superuser (root) has been partitioned into
a set of discrete capabilities.
Every thread has a set of effective capabilities identifying
which capabilities (if any) it may currently exercise.
Every thread also has a set of inheritable capabilities that may be
passed through an
execve(2)
call, and a set of permitted capabilities
that it can make effective or inheritable.
These two functions are the raw kernel interface for getting and
setting 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
cap_user_*_t
types) is subject to change with each kernel revision.
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).
Current details
Now that you have been warned, some current kernel details.
The structs are defined as follows.
#define _LINUX_CAPABILITY_VERSION 0x19980330
typedef struct __user_cap_header_struct {
int version;
int pid;
} *cap_user_header_t;
typedef struct __user_cap_data_struct {
int effective;
int permitted;
int inheritable;
} *cap_user_data_t;
The calls will return
R EINVAL ,
and set the
version
field of
hdr
to
_LINUX_CAPABILITY_VERSION
when another version was specified.
The calls operate on the capabilities of the thread specified by the
pid
field of
hdr
when that is non-zero, or on the capabilities of the calling thread if
pid
is 0.
If
pid
refers to a single-threaded process, then
pid
can be specified as a traditional process ID;
operating on a thread of a multithreaded process requires a thread ID
of the type returned by
gettid(2).
For
R capset (),
pid
can also be: -1, meaning perform the change on all threads except the
caller and
init(8);
or a value less than -1, in which case the change is applied
to all members of the process group whose ID is -
pid.
For details on the data, see
capabilities(7).
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
EFAULT
Bad memory address.
Neither of
hdrp
and
datap
may be NULL.
EINVAL
One of the arguments was invalid.
EPERM
An attempt was made to add a capability to the Permitted set, or to set
a capability in the Effective or Inheritable sets that is not in the
Permitted set.
EPERM
The caller attempted to use
R capset ()
to modify the capabilities of a thread other than itself,
but lacked sufficient privilege; the
CAP_SETPCAP
capability is required.
(A bug in kernels before 2.6.11 meant that this error could also
occur if a thread without this capability tried to change its
own capabilities by specifying the
pid
field as a non-zero value (i.e., the value returned by
getpid(2))
instead of 0.)
CONFORMING TO
These system calls are Linux specific.
NOTES
The portable interface to the capability querying and setting
functions is provided by the
libcap
library and is available from here:
ftp://ftp.kernel.org/pub/linux/libs/security/linux-privs
SEE ALSO
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