The C Standard, Section 7.2.1.1 [ISO/IEC 9899:2011], defines assert()
to have the following behavior:
The
assert
macro puts diagnostic tests into programs; it expands to a void expression. When it is executed, ifexpression
(which shall have a scalar type) is false (that is, compares equal to 0), theassert
macro writes information about the particular call that failed (including the text of the argument, the name of the source file, the source line number, and the name of the enclosing function—the latter are respectively the values of the pre-processing macros__FILE__
and__LINE__
and of the identifier__func__)
on the standard error stream in an implementation-defined format. It then calls theabort
function.
Because assert()
calls abort()
, cleanup functions registered with atexit()
are not called. If the intention of the programmer is to properly clean up in the case of a failed assertion, then runtime assertions should be replaced with static assertions where possible. (See DCL03-C. Use a static assertion to test the value of a constant expression.) When the assertion is based on runtime data, the assert
should be replaced with a runtime check that implements the adopted error strategy. (See ERR00-C. Adopt and implement a consistent and comprehensive error-handling policy.)
See ERR04-C. Choose an appropriate termination strategy for more information on program termination strategies and MSC11-C. Incorporate diagnostic tests using assertions for more information on using the assert()
macro.
Noncompliant Code Example
This noncompliant code example defines a function that is called before the program exits to clean up.
void cleanup(void) { /* Delete temporary files, restore consistent state, etc. */ } int main(void) { if (atexit(cleanup) != 0) { /* Handle error */ } /* ... */ assert(/* something bad didn't happen */); /* ... */ }
However, the code also has an assert
, and if the assertion fails, the cleanup()
function is not called.
Compliant Solution
In this compliant solution, the call to assert()
is replaced with an if
statement that calls exit()
to ensure that the proper termination routines are run.
void cleanup(void) { /* delete temporary files, restore consistent state, etc */ } int main(void) { if (atexit(cleanup) != 0) { /* Handle error */ } /* ... */ if (/* something bad happened */) { exit(EXIT_FAILURE); } /* ... */ }
Risk Assessment
Unsafe use of abort()
may leave files written in an inconsistent state. It may also leave sensitive temporary files on the file system.
Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
---|---|---|---|---|---|
ERR06-C | medium | unlikely | medium | P4 | L3 |
Automated Detection
Tool | Version | Checker | Description |
---|---|---|---|
Compass/ROSE |
|
| Can detect some violations of this rule. However, it can only detect violations involving |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
CERT C++ Secure Coding Standard: ERR06-CPP. Understand the termination behavior of assert() and abort()
ISO/IEC 9899:2011 Section 7.2.1.1, "The assert
macro," and Section 7.22.4.1, "The abort
function"
ISO/IEC PDTR 24772 "REU Termination strategy"