A signal is a mechanism for transferring control that is typically used to notify a process that an event has occurred. That process can then respond to that the event accordingly. The C standard provides Standard provides functions for sending and handling signals within a C program.
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void (*signal(int sig, void (*func)(int)))(int); |
This signal handler is conceptually equivalent to
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Some platforms provide the ability to mask signals while a signal handler is being processed. If a signal is masked while its own handler is processed, the handler is noninterruptible and need not be async-signal-safe. However, even when a signal is masked while its own handler is processed, the handler must still avoid invoking async-signal-safe unsafe functions because their execution may be (or have been) interrupted by another signal.
Vulnerabilities can arise if a signal handler that is not async-signal-safe is interrupted with any unmasked signal, including its own.
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POSIX recommends sigaction() and deprecates the use of signal() to register signal handlers. Unfortunately, sigaction() is not defined in the C standard and Standard and is consequently not as portable a solution.
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Interrupting a noninterruptible signal handler can result in a variety of vulnerabilities [Zalewski 2001].
Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
SIG00-C |
High |
Likely |
High | P9 | L2 |
Automated Detection
Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| CodeSonar |
| BADFUNC.SIGNAL | Use of signal | ||||||
| Helix QAC |
| C5019 | |||||||
| LDRA tool suite |
| 44 S | Enhanced enforcement | ||||||
| Parasoft C/C++test |
| CERT_C-SIG00-a | The signal handling facilities of <signal.h> shall not be used | ||||||
| PC-lint Plus |
| 586 | Assistance provided: reports use of the signal function |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
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| Insufficient synchronization |
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Bibliography
| [C99 Rationale 2003] | Subclause |
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| 5.2.3, "Signals and |
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| Interrupts" |
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| [Dowd 2006] | Chapter 13, "Synchronization and State" ("Signal |
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| Interruption and |
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| Repetition") |
| [ |
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| IEEE Std 1003.1:2013] | XSH, System Interface, longjmp |
| [OpenBSD] | signal() Man Page |
| [Zalewski 2001] | "Delivering Signals for Fun and Profit" |
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