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capsetp(3)

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_t,  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.

CONFORMING TO

   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 */;

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