ERR33-C. Check for error conditions

Many functions will either return a valid value or a value of the correct return type that indicates an error (for example, -1 or a null pointer). It is important that these function return values are checked to ensure that an error has not occurred. Otherwise, unpredictable results are possible.

Non-Compliant Code Example

In this example, input_string is copied into dynamically allocated memory referenced by str. However, the result of malloc(input_string_size) is not checked before str is referenced. Consequently, if malloc() fails, the program will abnormally terminate.

char *str = (char*)malloc(strlen(input_string) + 1);
strcpy(str, input_string); /* What if malloc() fails? */

Compliant Solution

The malloc() function, as well as the other memory allocation functions, returns either a null pointer or a pointer to the allocated space. Always test the returned pointer to make sure it is not equal to zero (NULL) before referencing the pointer. Handle the error condition appropriately when the returned pointer is equal to zero.

char *str = (char*)malloc(strlen(input_string) + 1);
if (str == NULL) {
  /* Handle Allocation Error */
}
strcpy(str, input_string);

Risk Assessment

Failing to detect error conditions can lead to unpredictable results, including abnormal program termination and denial-of-service attacks or, in some situations, could even allow an attacker to run arbitrary code.

Rule	Severity	Likelihood	Remediation Cost	Priority	Level
ERR30-C	3 (high)	3 (likely)	2 (medium)	P18	L1

Related Coding Practices

Coding Practice	Severity	Likelihood	Remediation Cost	Priority	Level
FLP03-C. Detect and handle floating point errors	low	probable	high	P2	L3
FLP32-C. Prevent or detect domain and range errors in math functions	medium	probable	medium	P8	L2
MEM32-C. Detect and handle memory allocation errors	high	likely	medium	P18	L1
FIO04-C. Detect and handle input and output errors	medium	probable	high	P4	L3
FIO33-C. Detect and handle input output errors resulting in undefined behavior	high	probable	medium	P12	L1
FIO35-C. Use feof() and ferror() to detect end-of-file and file errors when sizeof(int) == sizeof(char)	low	unlikely	medium	P2	L3
ERR00-C. Adopt and implement a consistent and comprehensive error-handling policy	medium	probable	high	P4	L3
ERR02-C. Avoid in-band error indicators	low	unlikely	high	P1	L3
ERR05-C. Application-independent code should provide error detection without dictating error handling	medium	probable	high	P4	L3
API04-C. Provide a consistent and usable error checking mechanism	medium	unlikely	medium	P2	L3
MSC02-C. Avoid errors of omission	low	likely	medium	P6	L2
MSC03-C. Avoid errors of addition	low	likely	medium	P6	L2

References

[[CWE]] CWE-252: Unchecked Error Condition
[[Henricson 97]] Recommendation 12.1 Check for all errors reported from functions

12. Error Handling (ERR) 13. Application Programming Interfaces (API)

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Non-Compliant Code Example

Compliant Solution

Risk Assessment

Related Coding Practices

References