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Code Block
bgColor#ccccff
langc
#include <signal.h>

void log_msg(int signum) {
  /* Log error message */
}

void handler(int signum) {
  /* Do some handling specific to SIGINT */
  if (raise(SIGUSR1) != 0) { /* violation */
    /* Handle error */
  }
}

int main(void) {

  signal(SIGUSR1, log_msg);
  signal(SIGINT, handler);
   
  /* program code */
  if (raise(SIGINT) != 0) {
    /* Handle error */
  }
  /* More code */

  return 0;
}

 

Implementation Details

 

POSIX

 

The following table from the the Open Group Base Specifications [Open Group 2004] defines a set of functions that are asynchronous-signal-safe. Applications may invoke these functions, without restriction, from a signal handler.

 

 Asynchronous-Signal-Safe Functions 

_Exit()

_exit()

abort()

accept()

access()

aio_error()

aio_return()

aio_suspend()

alarm()

bind()

cfgetispeed()

cfgetospeed()

cfsetispeed()

cfsetospeed()

chdir()

chmod()

chown()

clock_gettime()

close()

connect()

creat()

dup()

dup2()

execle()

execve()

fchmod()

fchown()

fcntl()

fdatasync()

fork()

fpathconf()

fstat()

fsync()

ftruncate()

getegid()

geteuid()

getgid()

getgroups()

getpeername()

getpgrp()

getpid()

getppid()

getsockname()

getsockopt()

getuid()

kill()

link()

listen()

lseek()

lstat()

mkdir()

mkfifo()

open()

pathconf()

pause()

pipe()

poll()

posix_trace_event()

pselect()

raise()

read()

readlink()

recv()

recvfrom()

recvmsg()

rename()

rmdir()

select()

sem_post()

send()

sendmsg()

sendto()

setgid()

setpgid()

setsid()

setsockopt()

setuid()

shutdown()

sigaction()

sigaddset()

sigdelset()

sigemptyset()

sigfillset()

sigismember()

sleep()

signal()

sigpause()

sigpending()

sigprocmask()

sigqueue()

sigset()

sigsuspend()

sockatmark()

socket()

socketpair()

stat()

symlink()

sysconf()

tcdrain()

tcflow()

tcflush()

tcgetattr()

tcgetpgrp()

tcsendbreak()

tcsetattr()

tcsetpgrp()

time()

timer_getoverrun()

timer_gettime()

timer_settime()

times()

umask()

uname()

unlink()

utime()

wait()

waitpid()

write()

 

 

 

All functions not listed in this table are considered to be unsafe with respect to signals. In the presence of signals, all functions defined by IEEE standard 1003.1-2001 behave as defined when called from or interrupted by a signal handler, with a single exception: when a signal interrupts an unsafe function and the signal handler calls an unsafe function, the behavior is undefined.

 

Note that although raise() is on the list of asynchronous-safe functions, it should not be called within a signal handler if the signal occurs as a result of abort() or raise() function.

 

Section 7.14.1.1, para. 4, of the C standard [ISO/IEC 9899:2011] states:

 

...

 If the signal occurs as the result of calling the abort or raise function, the signal handler shall not call the raise function.

 (See also undefined behavior 131 of Annex J.)

 

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OpenBSD

 

 The OpenBSD signal() man page identifies functions that are asynchronous-signal safe. Applications may consequently invoke them, without restriction, from a signal handler. 

The OpenBSD signal() manual page lists a few additional functions that are asynchronous-safe in OpenBSD but "probably not on other systems," including snprintf()vsnprintf(),and syslog_r()( but only when the syslog_data struct is initialized as a local variable).

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Tool

Version

Checker

Description

Compass/ROSE  Can detect violations of the rule for single-file programs.

LDRA tool suite

Include Page
LDRA_V
LDRA_V

88 D
89 D 

Fully implemented.

Splint

Include Page
Splint_V
Splint_V

 

 

 

Related Vulnerabilities

For an overview of software vulnerabilities resulting from improper signal handling, see Zalewski's paper on understanding, exploiting, and preventing signal-handling-related vulnerabilities [Zalewski 2001]. VU #834865 describes a vulnerability resulting from a violation of this rule.

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