Man Pages

cap_from_text(3) - phpMan cap_from_text(3) - phpMan

Command: man perldoc info search(apropos)  


CAP_FROM_TEXT(3)           Linux Programmer's Manual          CAP_FROM_TEXT(3)



NAME
       cap_from_text, cap_to_text, cap_to_name, cap_from_name - capability state textual representation translation

SYNOPSIS
       #include <sys/capability.h>

       cap_t cap_from_text(const char *buf_p);

       char *cap_to_text(cap_t caps, ssize_t *length_p);

       int cap_from_name(const char *name, cap_value_t *cap_p);

       char *cap_to_name(cap_value_t cap);

       Link with -lcap.

DESCRIPTION
       These  functions translate a capability state between an internal representation and a textual one.  The inter-
       nal representation is managed by the capability functions in working storage. The textual representation  is  a
       structured, human-readable string suitable for display.

       cap_from_text()  allocates  and initializes a capability state in working storage. It then sets the contents of
       this newly created capability state to the state represented  by  a  human-readable,  nul-terminated  character
       string  pointed  to by buf_p.  It returns a pointer to the newly created capability state.  When the capability
       state in working storage is no longer required, the  caller  should  free  any  releasable  memory  by  calling
       cap_free()  with  cap_t  as  an argument.  The function returns an error if it cannot parse the contents of the
       string pointed to by buf_p or does not recognize any capability_name or flag character as valid.  The  function
       also returns an error if any flag is both set and cleared within a single clause.

       cap_to_text() converts the capability state in working storage identified by cap_p into a nul-terminated human-
       readable string.  This function allocates any memory necessary to contain the string, and returns a pointer  to
       the  string.   If  the  pointer len_p is not NULL, the function shall also return the full length of the string
       (not including the nul terminator) in the location pointed to by len_p.  The capability state in working  stor-
       age,  identified  by  cap_p,  is  completely represented in the character string.  When the capability state in
       working storage is no longer required, the caller should free any releasable memory by calling cap_free()  with
       the returned string pointer as an argument.

       cap_from_name() converts a text representation of a capability, such as "cap_chown", to its numerical represen-
       tation (CAP_CHOWN=0), writing the decoded value into *cap_p.  If cap_p is NULL no result is  written,  but  the
       return  code  of  the  function  indicates  whether  or  not the specified capability can be represented by the
       library.

       cap_to_name() converts a capability index value, cap, to a libcap-allocated textual string. This string  should
       be deallocated with cap_free().

TEXTUAL REPRESENTATION
       A  textual representation of capability sets consists of one or more whitespace-separated clauses.  Each clause
       specifies some operations on a capability set; the set starts out with all capabilities lowered, and the  mean-
       ing of the string is the state of the capability set after all the clauses have been applied in order.

       Each  clause consists of a list of comma-separated capability names (or the word 'all'), followed by an action-
       list.  An action-list consists of a sequence of operator flag pairs.  Legal operators are: '=', '+',  and  '-'.
       Legal  flags are: 'e', 'i', and 'p'.  These flags are case-sensitive and specify the Effective, Inheritable and
       Permitted sets respectively.

       In the capability name lists, all names are case-insensitive.  The special name 'all' specifies  all  capabili-
       ties; it is equivalent to a list naming every capability individually.

       Unnamed capabilities can also be specified by number. This feature ensures that libcap can support capabilities
       that were not allocated at the time libcap was compiled. However, generally upgrading libcap will add names for
       recently allocated capabilities.

       The '=' operator indicates that the listed capabilities are first reset in all three capability sets.  The sub-
       sequent flags (which are optional when associated with this operator) indicate that the listed capabilities for
       the corresponding set are to be raised.  For example: "all=p" means lower every capability in the Effective and
       Inheritable sets but raise all of the Permitted capabilities; or, "cap_fowner=ep" means raise the Effective and
       Permitted override-file-ownership capability, while lowering this Inheritable capability.

       In  the  case  that  the  leading  operator is '=', and no list of capabilities is provided, the action-list is
       assumed to refer to 'all' capabilities.  For example, the following three clauses are equivalent to each  other
       (and indicate a completely empty capability set): "all="; "="; "cap_chown,<every-other-capability>=".

       The operators, '+' and '-' both require an explicit preceding capability list and one or more explicit trailing
       flags.  The '+' operator will raise all of the listed capabilities in the flagged  capability  sets.   The  '-'
       operator  will  lower all of the listed capabilities in the flagged capability sets.  For example: "all+p" will
       raise all of the Permitted capabilities; "cap_fowner+p-i" will raise the override-file-ownership capability  in
       the  Permitted capability set and lower this Inheritable capability; "cap_fowner+pe-i" and "cap_fowner=+pe" are
       equivalent.

RETURN VALUE
       cap_from_text(), cap_to_text() and cap_to_text() return a non-NULL value  on  success,  and  NULL  on  failure.
       cap_from_text() returns 0 for success, and -1 on failure (unknown capability).

       On failure, errno is set to EINVAL, or ENOMEM.

CONFORMING TO
       cap_from_text() and cap_to_text() are specified by the withdrawn POSIX.1e draft specification.  cap_from_name()
       and cap_to_name() are Linux extensions.

EXAMPLE
       The example program below demonstrates the use of cap_from_text() and cap_to_text().  The following shell  ses-
       sion shows a some example runs:

           $ ./a.out "cap_chown=p cap_chown+e"
           caps_to_text() returned "= cap_chown+ep"
           $ ./a.out "all=pe cap_chown-e cap_kill-pe"
           caps_to_text() returned "=ep cap_chown-e cap_kill-ep"

       The source code of the program is as follows:

       #include <stdlib.h>
       #include <stdio.h>
       #include <sys/capability.h>

       #define handle_error(msg) \
           do { perror(msg); exit(EXIT_FAILURE); } while (0)

       int
       main(int argc, char *argv[])
       {
           cap_t caps;
           char *txt_caps;

           if (argc != 2) {
               fprintf(stderr, "%s <textual-cap-set>\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           caps = cap_from_text(argv[1]);
           if (caps == NULL)
               handle_error("cap_from_text");

           txt_caps = cap_to_text(caps, NULL);
           if (txt_caps == NULL)
               handle_error("cap_to_text");

           printf("caps_to_text() returned \"%s\"\n", txt_caps);

           if (cap_free(txt_caps) != 0 || cap_free(caps) != 0)
               handle_error("cap_free");

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       libcap(3),  cap_clear(3), cap_compare(3), cap_copy_ext(3), cap_get_file(3), cap_get_proc(3), cap_init(3), capa-
       bilities(7)



                                  2008-05-10                  CAP_FROM_TEXT(3)