LOCRET.GLOB

Function returns address of local variable in a global variable

The LOCRET.GLOB checker finds instances in which a function returns the address of a local variable by writing it into a global variable.

Vulnerability and risk

Local variables are allocated on the stack, so when a function returns a pointer to the variable, it's returning a stack address. The address will be invalidated after returning from the function, so access will probably cause unexpected application behavior, typically a program crash.

Vulnerable code example

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  #include <stdlib.h>
  
  int *buf;
  
  void func_GLOB(unsigned n)
  {
      int aux;
      if (n == 1) {
          buf = &aux;
     } else {
         buf = (int *)malloc(n * sizeof(int));
     }
 }

Klocwork flags line 13 where control leaves function func_GLOB. This indicates that the address of the local variable, aux, which is assigned to a global variable at line 9, is accessible through that global variable after the function returns.

Related checkers

• LOCRET.ARG
• LOCRET.RET

External guidance

• CWE-416: Use After Free
• CWE-562: Return of Stack Variable Address
• CWE-672: Operation on a Resource after Expiration or Release
• CERT DCL30-C: Declare objects with appropriate storage durations

Security training

Application security training materials provided by Secure Code Warrior.

• Use After Free Training Video - Test your skills with a training example