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NAME | SYNOPSIS | DESCRIPTION | TEXTUAL REPRESENTATION | RETURN VALUE | CONFORMING TO | EXAMPLE | SEE ALSO | COLOPHON |
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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 *len_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 caps 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 caps, 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 and
"cap_fowner-i" will lower the override-file-ownership in the
Inheritable set.
The action list can consist of multiple operator flag pairs; the
actions are performed in left-to-right order. Thus, for example,
"cap_fowner+p-i" is equivalent to "cap_fowner+p cap_fowner-i".
As another example, "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 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_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/pub/scm/libs/libcap/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
⟨https://git.kernel.org/pub/scm/libs/libcap/libcap.git/⟩ on
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-05-18.) If you
discover any rendering problems in this HTML version 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
manual page), send a mail to man-pages@man7.org
2022-09-22 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), org.freedesktop.systemd1(5), systemd-system.conf(5), capabilities(7), captree(8), getcap(8), getpcaps(8), setcap(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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