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char *message;
int message_type;

/* Initialize message and message_type */

if (message_type == value_1) {
  /* Process message type 1 */
  free(message);
  message = NULL;
}
/* ... */
if (message_type == value_2) {
  /* Process message type 2 */
  free(message);
  message = NULL;
}

Exceptions

MEM01-C-EX1: If a nonstatic variable goes out of scope immediately following the free(), it is not necessary to clear its value because it is no longer accessible.

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Setting pointers to NULL or to another valid value after memory is freed is a simple and easily implemented solution for reducing dangling pointers. Dangling pointers can result in freeing memory multiple times or in writing to memory that has already been freed. Both of these problems can lead to an attacker executing arbitrary code with the permissions of the vulnerable process.

Automated Detection

Related Vulnerabilities

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

Related Guidelines

Bibliography

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