capget, capset — set/get capabilities
#undef _POSIX_SOURCE #include <sys/capability.h>
int
capget( |
cap_user_header_t | hdrp, |
| cap_user_data_t | datap); |
int
capset( |
cap_user_header_t | hdrp, |
| const cap_user_data_t | datap); |
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).
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 EINVAL, and set the version field of hdrp to _LINUX_CAPABILITY_VERSION when another
version was specified.
The calls operate on the capabilities of the thread
specified by the pid field of hdrp when that is nonzero, 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
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).
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
Bad memory address. Neither of hdrp and datap may be NULL.
One of the arguments was invalid.
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.
The caller attempted to use 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 nonzero value (i.e., the value returned by getpid(2)) instead of
0.)
No such thread.
The portable interface to the capability querying and
setting functions is provided by the libcap library and is
available here:
This page is part of release 2.79 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man-pages/.
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$Id: capget.2,v 1.4 1999/09/09 16:43:26 morgan Exp $ written by Andrew Morgan <morganlinux.kernel.org> may be distributed as per GPL Modified by David A. Wheeler <dwheelerida.org> Modified 2004-05-27, mtk Modified 2004-06-21, aeb |