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man pages section 3: Extended Library Functions, Volume 4

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Updated: Thursday, June 13, 2019



str_to_label - parse human readable strings to label


cc [flag...] file... -ltsol [library...]
#include <tsol/label.h>

int str_to_label(const char *string, m_label_t **label, 
    const m_label_type_t label_type, uint_t flags, int *error);


The str_to_label() function is a simple function to parse human readable strings into labels of the requested type.

The string argument is the string to parse. If string is the result of a label_to_str() conversion of type M_INTERNAL, flags are ignored, and any previously parsed label is replaced.

If *label is NULL, str_to_label() allocates resources for label and initializes the label to the label_type that was requested before parsing string.

If *label is not NULL, the label is a pointer to a mandatory label that is the result of a previously parsed label and label_type is ignored. The type that is used for parsing is derived from label for any type-sensitive operations.

If flags is L_MODIFY_EXISTING, the parsed string can be used to modify this label. The modifications are specified using + or - characters which indicate whether the classification or compartment should be added or removed. The parsed string syntax is as follows:

[+][classification] [[+|-][compartment]]...

where brackets denote optional entries, ... denotes zero or more of the proceeding bracketed entry can be specified with blanks preceding it. Blanks, tabs, commas, and slashes are interchangeable, with multiples allowed. Classifications and compartments themselves can contain blanks. If the parsed string starts with a classification followed by a + or -, then the new classification is used, but the rest of the label is retained and modified as specified in the parsed string.

If flags is L_NO_CORRECTION, the previously parsed label is replaced and the parsing algorithm does not attempt to infer missing elements from string to compose a valid label.

If flags is L_DEFAULT, the previously parsed label is replaced and the parsing algorithm makes a best effort to imply a valid label from the elements of string.

If flags contains L_CHECK_AR logically OR-ed with another value, the resulting label will be checked to ensure that it is within the “Accreditation Range” of the DIA encodings schema. This flag is interpreted only for MAC_LABEL label types.

The caller is responsible for freeing the allocated resources by calling the m_label_free() function. label_type defines the type for a newly allocated label. The label type can be:


The string should be translated as a Mandatory Access Control (MAC) label.


The string should be translated as a label that represents the least upper bound of the labels that the user is allowed to access.

If error is NULL, do not return additional error information for EINVAL. The calling process must have mandatory read access to label and human readable string. Or the calling process must have the sys_trans_label privilege.

The manifest constants ADMIN_HIGH and ADMIN_LOW are the human readable strings that correspond to the Trusted Extensions policy admin_high and admin_low label values. See labels(7).

Return Values

Upon successful completion, the str_to_label() function returns 0. Otherwise, -1 is returned, errno is set to indicate the error, and error provides additional information for EINVAL. Otherwise, error is a zero-based index to the string parse failure point.


The str_to_label() function will fail if:


Invalid parameter. M_BAD_STRING indicates that string could not be parsed. M_BAD_LABEL indicates that the label passed in was in error. M_OUTSIDE_AR indicates that the resulting label is not within the “Accreditation Range” specified in the DIA encodings schema.


The system does not support label translations.


The physical limits of the system are exceeded by size bytes of memory which cannot be allocated.


See attributes(7) for descriptions of the following attributes:

Interface Stability
See below.

Parsing types that are relative to Defense Intelligence Agency (DIA) encodings schema are Standard. Standard is specified in label_encodings(5).

See Also

libtsol(3LIB), label_to_str(3TSOL), m_label(3TSOL), label_encodings(5), attributes(7), labels(7)


A number of the parsing rules rely on the DIA label encodings schema. The rules might not be valid for other label schemata.