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Non-Compliant Coding Example
The This non-compliant program registers a single signal handler to clean up and terminate when the process receives either a SIGINT or a SIGTERM. However, if a SIGINT is generated, and then a SIGTERM is generated after the call to free(), but before _Exit() is reached, a double free() occurs. process both SIGUSR1 and SIGUSR2. The variable sig2 should be set to one if one or more SIGUSR1 signals are followed by SIGUSR2. a Note that this example also violates SIG30SIG31-C. Only call async-safe functions within Do not access or modify shared objects in signal handlers.
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#include <signal.h> #include <stdlib.h> char *global_ptr; void handler() { free(global_ptr); _Exit(-1); } int main(void) { global_ptr = malloc(16); if (global_ptr == NULL) { /* handle error condition */ }#include <string.h> volatile sig_atomic_t sig1 = 0; volatile sig_atomic_t sig2 = 0; void handler(int signum) { if (sig1) { sig2 = 1; } sig1 = 1; } int main(void) { signal(SIGINTSIGUSR1, handler); signal(SIGTERMSIGUSR2, handler); /* ... */ return 0; } |
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\[[ISO/IEC 03|AA. C References#ISO/IEC 03]\] Section 5.2.3, "Signals and Interruptsinterrupts" \[[Open Group 04|AA. C References#Open Group 04]\] [longjmp|http://www.opengroup.org/onlinepubs/000095399/functions/longjmp.html] \[OpenBSD\] [{{signal()}} Man Page|http://www.openbsd.org/cgi-bin/man.cgi?query=signal] \[Zalewski\] [http://lcamtuf.coredump.cx/signals.txt] \[[Dowd 06 | AA. C References#Dowd 06]\] Chapter 13, "Synchronization and State" (Signal Interruption and Repetition) |