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NAME | SYNOPSIS | DESCRIPTION | TEXTUAL REPRESENTATION | RETURN VALUE | CONFORMING TO | EXAMPLE | SEE ALSO | COLOPHON |
CAP_FROM_TEXT(3) Linux Programmer's Manual CAP_FROM_TEXT(3)
cap_from_text, cap_to_text, cap_to_name, cap_from_name - capability
state textual representation translation
#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.
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().
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.
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.
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.
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);
}
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)
This page is part of the libcap (capabilities commands and library)
project. Information about the project can be found at
⟨https://git.kernel.org/cgit/linux/kernel/git/morgan/libcap.git/⟩. If
you have a bug report for this manual page, send it to
morgan@kernel.org (please put "libcap" in the Subject line). This
page was obtained from the project's upstream Git repository
⟨git://git.kernel.org/pub/scm/linux/kernel/git/morgan/libcap.git⟩ on
2017-07-05. If you discover any rendering problems in this HTML ver‐
sion of the page, or you believe there is a better or more up-to-date
source for the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original man‐
ual page), send a mail to man-pages@man7.org
2008-05-10 CAP_FROM_TEXT(3)
Pages that refer to this page: capsh(1), cap_clear(3), cap_copy_ext(3), cap_get_file(3), cap_get_proc(3), cap_init(3), libcap(3), systemd-system.conf(5), capabilities(7), getcap(8), setcap(8)