bug#70628: segmentation fault reading socketpair after fork

[Jakov Tutavac <jakov.tutavac@gmail.com>]

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Dear Sir/Madam,

The 62 lines of code in the attachment result in a segmentation fault when
run.
I hope you can help suggest a fix or a workaround.

user@pcxy:~/$ guile --version
guile (GNU Guile) 3.0.7
Packaged by Debian (3.0.7-deb+3.0.7-1)

user@pcxy:~/$ make
gcc -I/usr/include/guile/3.0 -g -c -o main.o main.c
gcc -o a.out main.o -lguile-3.0 -lgc -lpthread -ldl
user@pcxy:~/$ ./a.out
Parent sv:3
Child sv:4
Segmentation fault (core dumped)

(gdb) r
Starting program: a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[Detaching after fork from child process 100100]

Parent sv:3
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7be68f2 in GC_find_limit_with_bound () from
/lib/x86_64-linux-gnu/libgc.so.1

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#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <fcntl.h>
#include <libguile.h>

static void *main_parent(void *arg)
{
	int sv = *((int *) arg);
	SCM port;
	char *buf = "Write from parent\n";

	printf("Parent sv:%d\n", sv);

	port = scm_fdopen(scm_from_int(dup(sv)), scm_from_utf8_stringn("r+", 2));
	scm_c_write(port, buf, sizeof(buf));
}

static void *main_child(void *arg)
{
	int sv = *((int *) arg);
	SCM port;
	char *buf = "                 \n";

	printf("Child sv:%d\n", sv);

	port = scm_fdopen(scm_from_int(dup(sv)), scm_from_utf8_stringn("r+", 2));
	scm_c_read(port, buf, sizeof(buf));
	printf("%s\n", buf);
}

int main(int argc, char *argv[])
{
	pid_t id;
	int sv[2];

	if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sv) != 0) {
		fprintf(stderr, "%s", strerror(errno));
		return EXIT_FAILURE;
	}

	id = fork();
	if (id == -1) {
		fprintf(stderr, "%s", strerror(errno));
		return EXIT_FAILURE;
	}

	if (id == 0) {
		/* parent process */
		scm_with_guile(main_parent, &sv[0]);
	} else {
		/* child process */
		scm_with_guile(main_child, &sv[1]);
	}
	wait(NULL);
	return EXIT_SUCCESS;
}