NAME¶
cap_get_proc, cap_set_proc, capgetp, cap_get_bound, cap_drop_bound - capability
manipulation on processes
SYNOPSIS¶
#include <sys/capability.h>
cap_t cap_get_proc(void);
int cap_set_proc(cap_t cap_p);
int cap_get_bound(cap_value_t cap);
CAP_IS_SUPPORTED(cap_value_t cap);
int cap_drop_bound(cap_value_t cap);
#include <sys/types.h>
cap_t cap_get_pid(pid_t pid);
Link with
-lcap.
DESCRIPTION¶
cap_get_proc() allocates a capability state in working storage, sets its
state to that of the calling process, and returns a pointer to this newly
created capability state. The caller should free any releasable memory, when
the capability state in working storage is no longer required, by calling
cap_free() with the
cap_t as an argument.
cap_set_proc() sets the values for all capability flags for all
capabilities to the capability state identified by
cap_p. The new
capability state of the process will be completely determined by the contents
of
cap_p upon successful return from this function. If any flag in
cap_p is set for any capability not currently permitted for the calling
process, the function will fail, and the capability state of the process will
remain unchanged.
cap_get_pid() returns
cap_d, see
cap_init(3), with the
process capabilities of the process indicated by
pid. This information
can also be obtained from the
/proc/<pid>/status file.
cap_get_bound() with a
cap as an argument returns the current
value of this bounding set capability flag in effect for the current process.
This operation is unpriveged. Note, a macro function
CAP_IS_SUPPORTED(cap_value_t cap) is provided that
evaluates to true (1) if the system supports the specified capability,
cap. If the system does not support the capability, this function
returns 0. This macro works by testing for an error condition with
cap_get_bound().
cap_drop_bound() can be used to lower the specified bounding set
capability,
cap, To complete successfully, the prevailing
effective capability set must have a raised
CAP_SETPCAP.
RETURN VALUE¶
The functions
cap_get_proc() and
cap_get_pid() return a non-NULL
value on success, and NULL on failure.
The function
cap_get_bound() returns -1 if the requested capability is
unknown, otherwise the return value reflects the current state of that
capability in the prevailing bounding set. Note, a macro function,
The functions
cap_set_proc() and
cap_drop_bound() return zero for
success, and -1 on failure.
On failure,
errno is set to
EINVAL,
EPERM, or
ENOMEM.
cap_set_proc() and
cap_get_proc() are specified in the withdrawn
POSIX.1e draft specification.
cap_get_pid() is a Linux extension.
NOTES¶
The library also supports the deprecated functions:
int capgetp(pid_t pid, cap_t cap_d);
int capsetp(pid_t pid, cap_t cap_d);
capgetp() attempts to obtain the capabilities of some other process;
storing the capabilities in a pre-allocated
cap_d.
See
cap_init() for information on allocating an empty capability set. This
function,
capgetp(), is deprecated, you should use
cap_get_pid().
capsetp() attempts to set the capabilities of some other process(es),
pid. If
pid is positive it refers to a specific process; if it
is zero, it refers to the current process; -1 refers to all processes other
than the current process and process '1' (typically
init(8)); other
negative values refer to the
-pid process group. In order to use this
function, the kernel must support it and the current process must have
CAP_SETPCAP raised in its Effective capability set. The capabilities
set in the target process(es) are those contained in
cap_d. Kernels
that support filesystem capabilities redefine the semantics of
CAP_SETPCAP and on such systems this function will always fail for any
target not equal to the current process.
capsetp() returns zero for
success, and -1 on failure.
Where supported by the kernel, the function
capsetp() should be used with
care. It existed, primarily, to overcome an early lack of support for
capabilities in the filesystems supported by Linux. Note that, by default, the
only processes that have
CAP_SETPCAP available to them are processes
started as a kernel thread. (Typically this includes
init(8), kflushd
and kswapd). You will need to recompile the kernel to modify this default.
EXAMPLE¶
The code segment below raises the
CAP_FOWNER and
CAP_SETFCAP
effective capabilities for the caller:
cap_t caps;
cap_value_t cap_list[2];
if (!CAP_IS_SUPPORTED(CAP_SETFCAP))
/* handle error */
caps = cap_get_proc();
if (caps == NULL)
/* handle error */;
cap_list[0] = CAP_FOWNER;
cap_list[1] = CAP_SETFCAP;
if (cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_list, CAP_SET) == -1)
/* handle error */;
if (cap_set_proc(caps) == -1)
/* handle error */;
if (cap_free(caps) == -1)
/* handle error */;
SEE ALSO¶
libcap(3),
cap_clear(3),
cap_copy_ext(3),
cap_from_text(3),
cap_get_file(3),
cap_init(3),
capabilities(7)