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Opening and closing braces for if, for, or and while statements should always be used , even if said the statement's body contains only a single statement.

In the event that either of these statements are If an if, while, or for statement is used in a macro, this implies that the macro definition should not be concluded conclude with a semicolon. (see See PRE11-C. Do not conclude macro definitions with a semicolon.).

Braces help improve the uniformity , and therefore readability of code. More importantlyimportant, when inserting an additional statement in into a body containing only a single statement, it is easy to forget to add braces when because the indentation tends to give a gives strong (but probably misleading) guide guidance to the structure.

Braces also help ensure that macros with multiple statements are properly expanded. Such a macro should be wrapped in a do-while loop. (See PRE10-C. Wrap multistatement macros in a do-while loop.) However, when the do-while loop is not present, braces can still ensure that the macro expands as intended.

Noncompliant Code Example

This noncompliant code example uses an if-else statement without braces to authenticate a user.:

int login;

if (invalid_login())
  login = 0;
else
  login = 1;

The programmer adds A developer might add a debugging statement to determine when the login is valid , but forgets forget to add opening and closing braces.:

int login;

if (invalid_login())
  login = 0;
else
  printf("Login is valid\n");  /* debuggingDebugging line added here */
  login = 1;                   /* thisThis line always gets executed,
                               /* regardless of a valid login! */

Due to the Because of the indentation of the code, it is difficult to tell that the code is will not functioning function as intended by the programmer, potentially leading to a possible security breach.

Compliant Solution

Opening In the compliant solution, opening and closing braces are used even when the body is a single statement.:

int login;

if (invalid_login()) {
  login = 0;
} else {
  login = 1;
}

Noncompliant Code Example

When you have This noncompliant code example has an if-else statement nested in another if statement , always put without braces around the if-else. This noncompliant code example does not use braces. and else bodies:

int privileges;

if (invalid_login())
  if (allow_guests())
    privileges = GUEST;
else
  privileges = ADMINISTRATOR;

According to the indentation, The indentation could lead the programmer may be led to believe that a user is given administrator privileges only when his the user's login is valid. However, in reality, the else statement actually attaches to the inner if statement, like so:

int privileges;

if (invalid_login())
  if (allow_guests())
    privileges = GUEST;
  else
    privileges = ADMINISTRATOR;

This is a security loophole - : users with invalid logins can still obtain administrator privileges.

Compliant Solution

Adding In the compliant solution, adding braces removes the ambiguity and ensures that privileges are correctly assigned.:

int privileges;

if (invalid_login()) {
  if (allow_guests()) {
    privileges = GUEST;
  } 
} else {
  privileges = ADMINISTRATOR;
}

Noncompliant Code Example (empty block)

This noncompliant code example has a while statement with no block:

while (invalid_login());

Note that if invalid_login() has no side effects (such as warning the user if their login failed), this code also violates MSC12-C. Detect and remove code that has no effect or is never executed.

Compliant Solution (empty block)

This compliant solution features an explicit empty block, which clarifies the developer's intent:

while (invalid_login()) {}

Risk Assessment

References

Automated Detection

Related Vulnerabilities

CVE-2014-1266 was due, in large part, to failing to follow this recommendation. There is a spurious "goto fail" statement on line 631 of sslKeyExchange.c. This "goto" gets executed unconditionally, even though it is indented as if it were part of the preceding "if" statement.  As a result, the call to sslRawVerify (which performs the actual signature verification) is rendered dead code.  [ImperialViolet 2014]. If the body of the "if" statement had been enclosed in braces, then this defect likely would not have happened.

Related Guidelines

 Bibliography

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Image Added Image Added Image Added Wiki Markup\[[ISO/IEC 9899-1999|AA. References#ISO/IEC 9899-1999]\] Section 6.8.4, "Selection statements" \[[MISRA 04|AA. References#MISRA 04]\] Rule 14.8 \[[GNU Coding Standards|http://www.gnu.org/prep/standards/standards.html#Syntactic-Conventions]\] Section 5.3, "Clean Use of C Constructs"