Page History

Wiki MarkupThe managed string library described in \ [[Burch 2006|AA. Bibliography#Burch06] \] was developed in response to the need for a string library that could improve the quality and security of newly developed C language code while eliminating obstacles to widespread adoption and possible standardization.

The managed string library is based on a dynamic approach in which memory is allocated and reallocated as required. This approach eliminates the possibility of unbounded copies, null-termination errors, and truncation by ensuring there is always adequate space available for the resulting string (including the terminating null character).

...

errno_t retValue;
char *cstr;  /* pointer to null-terminated byte string */
string_mx *str1 = NULL;

retValue = strcreate_m(&str1, "hello, world", 0, NULL);
if (retValue != 0) {
  fprintf(stderr, "Error %d from strcreate_m.\n", retValue);
}
else { /* retrieve null-terminated byte string and print */
  retValue = getstr_m(&cstr, str1);
  if (retValue != 0) {
    fprintf(stderr, "error %d from getstr_m.\n", retValue);
  }
  printf("(%s)\n", cstr);
  free(cstr); /* free null-terminated byte string */
  cstr = NULL;
}

...

Note that the calls to {{fprintf()}} and {{printf()}} are C99 \[ [ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999] \] standard functions and not managed string functions.

The forthcoming technical report ISO/IEC TR 24731-2 will also provide an API that dynamically allocates the results of string functions as needed.

Risk Assessment

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String handling functions defined in C99 \[ [ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\], Section 7.21 and elsewhere are susceptible to common programming errors that can lead to serious, exploitable [vulnerabilities|BB. Definitions#vulnerability]. Managed strings, when used properly, can eliminate many of these errors, particularly in new development.

Recommendation	Severity	Likelihood	Remediation Cost	Priority	Level
STR08-C	high	probable	high	P6	L2

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

...

ISO/IEC 9899:1999 Section 7.21, "String handling <string.h>"

Bibliography

Wiki Markup\[[Burch 2006|AA. Bibliography#Burch06]\] \[]
[CERT 2006c|AA. Bibliography#CERT 06c]\] \[[Seacord 2005a|AA. Bibliography#Seacord 05a]\] Chapter 2, ]
[Seacord 2005a] Chapter 2, "Strings"

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STR07-C. Use the bounds-checking interfaces for remediation of existing string manipulation code      07. Characters and Strings (STR)