Hello Theodore,
I created the test program below.
While running it I issued
kill -SIGUSR1 <pid>
and
kill -SIGUSR2 <pid>
What I found was rather strange.
No matter whether specifying GRND_NONBLOCK or not, signals do not
interrupt the execution of getrandom() while reading from the
/dev/urandom pool.
Only after getrandom has finished signals are handled.
I would have expected getrandom() to react to interrupts immediately and
to return whatever number of random bytes have been collected before the
interrupt.
A system call not reacting to interrupts for several seconds looks like
a bug to me.
Tested on Linux 3.18.0-rc4 mips64.
Best regards
Heinrich Schuchardt
#define _GNU_SOURCE
#include <errno.h>
#include <linux/unistd.h>
#include <linux/random.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/syscall.h>
#include <sys/types.h>
#if _MIPS_SIM == _MIPS_SIM_ABI32
#define __NR_getrandom (__NR_Linux + 353)
#endif /* _MIPS_SIM == _MIPS_SIM_ABI32 */
#if _MIPS_SIM == _MIPS_SIM_ABI64
#define __NR_getrandom (__NR_Linux + 313)
#endif /* _MIPS_SIM == _MIPS_SIM_ABI64 */
#if _MIPS_SIM == _MIPS_SIM_NABI32
#define __NR_getrandom (__NR_Linux + 317)
#endif /* _MIPS_SIM == _MIPS_SIM_NABI32 */
#ifdef __i386__
#define __NR_getrandom (355)
#endif /* __i386__ */
#ifdef __x86_64__
#define __NR_getrandom (318)
#endif /* __x86_64__ */
#define SYS_getrandom __NR_getrandom
#define GRND_NONBLOCK 0x0001
#define GRND_RANDOM 0x0002
#define BUFLEN 0x12345678
int getrandom(void *buf, size_t buflen, unsigned int flags)
{
return syscall(SYS_getrandom, buf, buflen, flags);
}
/**
* Handles signal.
*
* @param sig signal
*/
int do_print = 0;
static void hdl(int sig)
{
if (sig == SIGUSR1) {
fprintf(stderr, "Main received SIGUSR1\n");
do_print = 1;
}
}
int
main(int argc, char *argv[])
{
char *buf;
size_t buflen = BUFLEN;
int ret;
pid_t pid;
// action to take when signal occurs
struct sigaction act;
// signal mask
sigset_t blockset;
pid = getpid();
printf("PID = %u\n", pid);
printf("__NR_getrandom = %u\n", __NR_getrandom);
// Set handler for SIGUSR1
act.sa_handler = hdl;
sigemptyset(&act.sa_mask);
act.sa_flags = 0;
if (sigaction(SIGUSR1, &act, NULL)) {
perror("sigaction");
exit(EXIT_FAILURE);
}
buf = (char *) malloc(buflen);
if (buf == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
buf = (char *) malloc(buflen);
for (;;) {
ret = getrandom(buf, buflen, GRND_NONBLOCK);
if (ret == -1) {
fprintf(stderr, "errno = %d\n", errno);
perror("getrandom");
exit(EXIT_FAILURE);
}
if (do_print) {
do_print = 0;
printf("ret = %d\n", ret);
}
}
printf("ret = %d\n", ret);
free(buf);
return EXIT_SUCCESS;
}
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