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Overflow in uncontrolled allocation size

ID: cpp/uncontrolled-allocation-size
Kind: path-problem
Security severity: 8.1
Severity: error
Precision: medium
Tags:
   - reliability
   - security
   - external/cwe/cwe-190
   - external/cwe/cwe-789
Query suites:
   - cpp-security-extended.qls
   - cpp-security-and-quality.qls

Click to see the query in the CodeQL repository

This code calculates an allocation size by multiplying a user input by a sizeof expression. Since the user input has no apparent guard on its magnitude, this multiplication can overflow. When an integer multiply overflows in C, the result can wrap around and be much smaller than intended. A later attempt to put data into the allocated buffer can then overflow.

Recommendation

Guard all integer parameters that come from an external user. Implement a guard with the expected range for the parameter and make sure that the input value meets both the minimum and maximum requirements for this range. If the input value fails this guard then reject the request before proceeding further. If the input value passes the guard then subsequent calculations should not overflow.

Example

int factor = atoi(getenv("BRANCHING_FACTOR"));

// GOOD: Prevent overflow by checking the input
if (factor < 0 || factor > 1000) {
    log("Factor out of range (%d)\n", factor);
    return -1;
}

// This line can allocate too little memory if factor
// is very large.
char **root_node = (char **) malloc(factor * sizeof(char *));

This code shows one way to guard that an input value is within the expected range. If factor fails the guard, then an error is returned, and the value is not used as an argument to the subsequent call to malloc. Without this guard, the allocated buffer might be too small to hold the data intended for it.

References

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