Page History

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const char *p;
void dont_do_this(void) {
    const char str[] = ""This will change"";
    p = str; /* dangerous */
    /* ... */
}

void innocuous(void) {
    const char str[] = ""Surprise, surprise"";
}
/* ... */
dont_do_this();
innocuous();
/* p might be pointing to ""Surprise, surprise"" */

As a result of this undefined behavior, it is likely that p will refer to the string literal "Surprise, surprise" after the call to the innocuous() function.

...

void this_is_OK(void) {
    const char str[] = ""Everything OK"";
    const char *p = str;
    /* ... */
}
/* p is inaccessible outside the scope of string str */

...

const char *p;
void is_this_OK(void) {
    const char str[] = ""Everything OK?"";
    p = str;
    /* ... */
    p = NULL;
}

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Automated Detection

The LDRA tool suite Version 7.6.0 can detect violations of this rule.

Fortify SCA Version 5.0 can detect violations when an array is declared in a function and then a pointer to that array is returned.

Splint Version 3.1.1 can detect violations of this rule.

Compass/ROSE can detect violations of this rule. It automatically detects returning pointers to local variables. Detecting more general cases, such as examples where static pointers are set to local variables which then go out of scope would be difficult.

The Coverity Prevent RETURN_LOCAL checker finds many instances where a function will return a pointer to a local stack variable. Coverity Prevent cannot discover all violations of this rule, so further verification is necessary.

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Tool	Compliance
GCC	n/a
Rose	partial
LDRA	yes
Fortify	yes
Coverity	RETURN_LOCAL
Splint	yes
Klocwork	LOCRET

Related Vulnerabilities

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

Other Languages

This rule appears in the C++ Secure Coding Standard as DCL30-CPP. Declare objects with appropriate storage durations.

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Bibliographyerences

\[[Coverity 07|AA. C References#Coverity 07]\]
\[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.2.4, ""Storage durations of objects,"" and Section 7.20.3, ""Memory management functions""
\[[ISO/IEC PDTR 24772|AA. C References#ISO/IEC PDTR 24772]\] ""DCM Dangling references to stack frames""
\[[MISRA 04|AA. C References#MISRA 04]\] Rule 8.6

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DCL16-C. Use 'L', not 'l', to indicate a long value            02. Declarations and Initialization (DCL)