cap_from_text

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 internal 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 storage, 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 representation (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 meaning 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 capabilities; 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 subsequent 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_name() return a non-NULL
       value on success, and NULL on failure.  cap_from_name() 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 session 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), capabilities(7)



                                  2008-05-10                  CAP_FROM_TEXT(3)