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 event accordingly. C99 provides functions for sending and handling signals within a C program.
Signals are handled by a process by registering a signal handler using the signal() function, which is specified as:
void (*signal(int sig, void (*func)(int)))(int);
There are two kinds of signal: synchronous (as initiated by a call to raise or abort) and asynchronous. Most of the rules and recommendations in this section do not apply toFor signals that are invoked synchronously, as there is no significant difference between signal handlers that are invoked by a call to a library function and signal handlers that are invoked by a call to the handler itself.
Improper handling of signals can lead to security vulnerabilities. The following rules and recommendations are meant to eliminate common errors associated with signal handling.
Recommendations
SIG00-A. Mask signals handled by non-interruptible signal handlers
SIG01-A. Understand implementation-specific details regarding signal handler persistence
Rules
SIG30-C. Call only asynchronous-safe functions within signal handlers
SIG31-C. Do not access or modify shared objects in signal handlers
SIG32-C. Do not call longjmp() from inside a signal handler
SIG33-C. Do not recursively invoke the raise() function
SIG34-C. A signal handler should not re-assert itself
Risk Assessment Summary
Recommendation |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
SIG00-A |
3 (high) |
3 (likely) |
1 (high) |
P9 |
L2 |
SIG01-A |
1 (low) |
1 (unlikely) |
3 (low) |
P3 |
L3 |
Rule |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
SIG30-C |
3 (high) |
3 (likely) |
1 (high) |
P9 |
L2 |
SIG31-C |
3 (high) |
3 (likely) |
1 (high) |
P9 |
L2 |
SIG32-C |
3 (high) |
3 (likely) |
1 (high) |
P9 |
L2 |
SIG33-C |
1 (low) |
1 (unlikely) |
2 (medium) |
P2 |
L3 |
SIG34-C |
1 (low) |
1 (unlikely) |
3 (low) |
P3 |
L3 |
ENV33-C. Do not call the longjmp function to terminate a call to a function registered by atexit() 11. Environment (ENV)