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In this noncompliant example, the char pointer &c is converted to the more strictly aligned int pointer i_ptr.:

void f(void) {
  int *i_ptr;
  char c;
 
  i_ptr = (int *)&c;  /* violation */
  /* ... */
}

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In this compliant solution, the value referenced by the char pointer c_ptr has the alignment of type int.:

void f(void) {
  char *c_ptr;
  int *i_ptr;
  int i;
 
  c_ptr = (char *)&i;
  i_ptr = (int *)c_ptr;
  /* ... */
}

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Because the input parameter directly influences the return value, and loop_function() returns an int *, the formal parameter v_pointer is redeclared to only accept int *.:

int *loop_ptr;
int *int_ptr;

int *loop_function(int *v_pointer) {
  /* ... */
  return v_pointer;
}
int_ptr = loop_function(loop_ptr);

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Many architectures require that pointers are correctly aligned when accessing objects larger than a byte. There are, however, many places in system code where you receive unaligned data (for example, the network stacks) that needs to be copied to a properly aligned memory location, such as in this noncompliant code example.:

char *data;
struct foo_header *tmp;
struct foo_header *header;

tmp = data + offset;
memcpy(&header, tmp, sizeof(header));

if (header.len < FOO)
/* ... */

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This compliant solution does not use the foo_header pointer.:

char *data;
struct foo_header header;

memcpy(&header, data + offset, sizeof(header));

if (header.len < FOO)
/* ... */

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For objects declared on the stack, the C Standard provides alignas to declare an object to have a stricter alignment. It can be used to resolve the following noncompliant code example.:

char c = 'x';
int *ip = (int *)&c; /* this can lose information */
char *cp = (char *)ip;
assert(cp == &c);    /* will fail on some conforming implementations */

Compliant Solution

The This compliant solution uses alignas to align the the character c to the alignment of an integer. As a result, the two pointers point to equally aligned pointer types.:

alignas(int) char c = 'x'; /* align c to the alignment of an int */
int *ip = (int *)&c; 
char *cp = (char *)ip;
assert(cp == &c);    /* both cp and &c point to equally aligned objects */

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Related Vulnerabilities

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

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Bibliography

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