NAME

       cap_get_file, cap_set_file, cap_get_fd, cap_set_fd - capability manipulation on files

SYNOPSIS

       #include <sys/capability.h>

       cap_t cap_get_file(const char *path_p);

       int cap_set_file(const char *path_p, cap_t cap_p);

       cap_t cap_get_fd(int fd);

       int cap_set_fd(int fd, cap_t caps);

       uid_t cap_get_nsowner(cap_t caps);

       int cap_set_nsowner(cap_t caps, uid_t rootuid);

       Link with -lcap.

DESCRIPTION

       cap_get_file()  and  cap_get_fd()  allocate a capability state in working storage and set it to represent
       the capability state of the pathname pointed to by path_p or the  file  open  on  descriptor  fd.   These
       functions  return a pointer to the newly created capability state.  The effects of reading the capability
       state from any file other than a regular file is  undefined.   The  caller  should  free  any  releasable
       memory,  when  the  capability state in working storage is no longer required, by calling cap_free() with
       the used cap_t as an argument.

       cap_set_file() and cap_set_fd() set the values for all capability flags  for  all  capabilities  for  the
       pathname  pointed to by path_p or the file open on descriptor fd, with the capability state identified by
       cap_p.  The new capability state of the file is completely determined by the contents of cap_p.   A  NULL
       value  for  cap_p  is  used  to  indicate  that  capabilities  for the file should be deleted.  For these
       functions to succeed, the calling process must have the CAP_SETFCAP capability in its effective  set  and
       either  the  effective  user ID of the process must match the file owner or the calling process must have
       the CAP_FOWNER capability in its effective capability set.  The effects of writing the  capability  state
       to any file type other than a regular file are undefined.

       A  capability  set  held  in  memory  can  be  associated with the root user ID in use in a specific user
       namespace. It is possible to get and set this value (in  the  memory  copy)  with  cap_get_nsowner()  and
       cap_set_nsowner() respectively. The root user ID is ignored by the libcap library in all cases other than
       when the capability is written to a file. Only if the value is  non-zero  will  the  library  attempt  to
       include it in the written file capability set.

RETURN VALUE

       cap_get_file() and cap_get_fd() return a non-NULL value on success, and NULL on failure.

       cap_set_file() and cap_set_fd() return zero on success, and -1 on failure.

       On failure, errno is set to EACCES, EBADFD, ENAMETOOLONG, ENOENT, ENOMEM, ENOTDIR, EPERM, or EROFS.

CONFORMING TO

       These functions are specified by withdrawn POSIX.1e draft specification.

NOTES

       Support for file capabilities is provided on Linux since version 2.6.24.

       On  Linux, the file Effective set is a single bit.  If it is enabled, then all Permitted capabilities are
       enabled in the Effective set of the calling process when the file is executed; otherwise, no capabilities
       are  enabled  in the process's Effective set following an execve(2).  Because the file Effective set is a
       single bit, if any capability is enabled in the Effective set of the cap_t  given  to  cap_set_file()  or
       cap_set_fd(),  then  all  capabilities  whose Permitted or Inheritable flag is enabled must also have the
       Effective flag enabled.  Conversely, if the Effective bit is enabled on a file, then the  cap_t  returned
       by  cap_get_file() and cap_get_fd() will have the Effective flag enabled for each capability that has the
       Permitted or Inheritable flag enabled.

SEE ALSO

       libcap(3),    cap_clear(3),    cap_copy_ext(3),    cap_from_text(3),    cap_get_proc(3),     cap_init(3),
       capabilities(7), user_namespaces(7)

                                                   2008-05-11                                    CAP_GET_FILE(3)