Capability manipulation on processes
#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.
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.
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cap_set_proc() and cap_get_proc() are specified in the withdrawn POSIX.1e draft specification.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.
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.
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 */;