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Top Forums Programming How to block or ignore signals from certain processes? Post 302233564 by aaronwong on Monday 8th of September 2008 04:02:26 AM
Old 09-08-2008
Lightbulb How to block or ignore signals from certain processes?

We know that a process can block certain signals by call sigprocmask(), but sometimes we may want to block signals from certain processes for safety concerning.

For example, a system may have a process management daemon, and it will response to certain signals from certain processes managed by it. A process in this system may have certain request by sending certain signals to the process manager, in this case, if the process manager just response according to the received signal value without checking the signal sender, then other hacker processes may disguise to attack the system. Therefore, it is critical to block signals from other processes that the process manager does not recognize.

Of course, we can check the pid of signal senders in the signal handler, but it may seem awkard if there are dozens of processes monitored by the process manager.
Is there any neat method to block or ignore signals from certain processes ?

Thank you in advance !
 

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sigprocmask(2)															    sigprocmask(2)

NAME
sigprocmask - change or examine caller's signal mask SYNOPSIS
#include <signal.h> int sigprocmask(int how, const sigset_t *restrict set, sigset_t *restrict oset); The sigprocmask() function is used to examine and/or change the caller's signal mask. If the value is SIG_BLOCK, the set pointed to by the set argument is added to the current signal mask. If the value is SIG_UNBLOCK, the set pointed by the set argument is removed from the current signal mask. If the value is SIG_SETMASK, the current signal mask is replaced by the set pointed to by the set argument. If the oset argument is not NULL, the previous mask is stored in the space pointed to by oset. If the value of the set argument is NULL, the value how is not significant and the caller's signal mask is unchanged; thus, the call can be used to inquire about currently blocked sig- nals. If the set or oset argument points to an invalid address, the behavior is undefined and errno may be set to EFAULT. If there are any pending unblocked signals after the call to sigprocmask(), at least one of those signals will be delivered before the call to sigprocmask() returns. It is not possible to block signals that cannot be caught or ignored (see sigaction(2)). It is also not possible to block or unblock SIG- CANCEL, as SIGCANCEL is reserved for the implementation of POSIX thread cancellation (see pthread_cancel(3C) and cancellation(5)). This restriction is silently enforced by the standard C library. If sigprocmask() fails, the caller's signal mask is not changed. Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error. The sigprocmask() function will fail if: EINVAL The value of the how argument is not equal to one of the defined values. The sigprocmask() function may fail if: EFAULT The set or oset argument points to an illegal address. See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ sigaction(2), pthread_cancel(3C), pthread_sigmask(3C), signal(3C), signal.h(3HEAD), sigsetops(3C), attributes(5), cancellation(5) The call to sigprocmask() affects only the calling thread's signal mask. It is identical to a call to pthread_sigmask(3C). Signals that are generated synchronously should not be masked. If such a signal is blocked and delivered, the receiving process is killed. 23 Mar 2005 sigprocmask(2)
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