Problem - Kevin Tafuro

We strongly recommend against performing complex operations in a signal handler.
If you feel that it’s necessary, be aware that it can be done but is error-prone and will
negatively affect program performance.
As an example of what you must do to safely use malloc( ) (whether directly or indirectly)
from inside a signal handler, note that any time malloc( ) needs to be called
inside or outside the signal handler, signal delivery will need to be blocked before the
call to malloc( ) and unblocked again after the call. Changing the signal delivery
often incurs a context switch from user mode to kernel mode; when such switching
is done so frequently, it can quickly add up to a significant decrease in performance.
In addition, because you may never be certain which functions may call malloc( )
under the covers, you may need to protect everything, which can easily result in forgotten
protections in places.
Discussion
As we have already mentioned, there is unfortunately no cookie-cutter solution to
writing safe signal handlers. The code presented here is simply an example of how
signal handlers can be properly written. A much more detailed discussion of signal
handling, which includes real-world examples of how improperly written signal handlers
can be exploited, can be found in Michal Zalewski’s paper, “Delivering Signals
for Fun and Profit,” which is available at http://www.netsys.com/library/papers/
signals.txt. Another excellent source of information regarding the proper way to
write signal handlers is Advanced Programming in the Unix Environment by W. Richard
Stevens (Addison Wesley).
#include
#include
#include
int sigint_received = 0;
int sigterm_received = 0;
int sigquit_received = 0;
void handle_sigint(int sig) { sigint_received = 1; }
void handle_sigterm(int sig) { sigterm_received = 1; }
void handle_sigquit(int sig) { sigquit_received = 1; }
static void setup_signal_handler(int sig, void (*handler)( )) {
#if _POSIX_VERSION > 198800L
struct sigaction action;
action.sa_handler = handler;
sigemptyset(&(action.sa_mask));
sigaddset(&(action.sa_mask), sig);
action.sa_flags = 0;
sigaction(sig, &action, 0);
#else
signal(sig, handler);
714 | Chapter 13: Other Topics
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