MSC06-A. Avoid race conditions with multiple threads

When multiple threads can read or modify the same data, use mutual exclusion primitives to avoid software flaws that could lead to security vulnerabilities. Concurrency problems can often result in abnormal termination or denial of service, but it is possible for them to result in more serious vulnerabilities.

Non-Compliant Code Example

int account_balance;

void debit(int amount)
{
  account_balance \-= amount;
}

void credit(int amount)
{
  account_balance \+= amount;
}

Compliant Solution

int account_balance;
mutex_t account_lock;

void debit(int amount)
{
  mutex_lock(&account_lock);
  account_balance \-= amount;
  mutex_unlock(&account_lock);
}

void credit(int amount)
{
  mutex_lock(&account_lock);
  account_balance \+= amount;
  mutex_unlock(&account_lock);
}

Risk Assessment

Race conditions caused by multiple threads concurrently accessing and modifying the same data could lead to abnormal termination and denial-of-service attacks, or in cases like the above data integrity violation.

References

[[Seacord 05]] Chapter 7, "File I/O"