// https://syzkaller.appspot.com/bug?id=94a5bd822dcdb0024919441e2a8c7720380df06f
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <pthread.h>
#include <string.h>
#include <errno.h>

pthread_barrier_t barrier;

void *thread_bc(void *arg) {
    char target[256];
    for (int i = 0; i < 10000; i++) {
        char buf[256];
        sprintf(buf, "lower/b_%d", i);
        
        pthread_barrier_wait(&barrier);
        readlink(buf, target, sizeof(target));
    }
    return NULL;
}

int main() {
    setvbuf(stdout, NULL, _IONBF, 0);
    printf("[*] Starting reproducer...\n");

    if (mkdir("lower", 0777) < 0 && errno != EEXIST) {
        printf("[-] Failed to mkdir lower: %s\n", strerror(errno));
        exit(1);
    }
    if (mkdir("upper", 0777) < 0 && errno != EEXIST) {
        printf("[-] Failed to mkdir upper: %s\n", strerror(errno));
        exit(1);
    }
    if (mkdir("work", 0777) < 0 && errno != EEXIST) {
        printf("[-] Failed to mkdir work: %s\n", strerror(errno));
        exit(1);
    }
    if (mkdir("merged", 0777) < 0 && errno != EEXIST) {
        printf("[-] Failed to mkdir merged: %s\n", strerror(errno));
        exit(1);
    }

    printf("[+] Directories created successfully.\n");

    if (mount("overlay", "merged", "overlay", 0, "lowerdir=lower,upperdir=upper,workdir=work") != 0) {
        printf("[-] Failed to mount overlay: %s\n", strerror(errno));
        exit(1);
    }
    printf("[+] Overlayfs mounted successfully.\n");

    // Phase 1: Record DCACHE_PAR_LOOKUP -> lower_dir_lock
    printf("[*] Phase 1: Recording DCACHE_PAR_LOOKUP -> lower_dir_lock...\n");
    for (int i = 0; i < 100; i++) {
        char buf[256];
        sprintf(buf, "merged/a_%d", i);
        int fd = open(buf, O_CREAT | O_RDWR, 0666);
        if (fd >= 0) close(fd);
    }
    printf("[+] Phase 1 completed.\n");

    // Phase 2: Record lower_dir_lock -> DCACHE_PAR_LOOKUP
    printf("[*] Phase 2: Recording lower_dir_lock -> DCACHE_PAR_LOOKUP...\n");
    if (pthread_barrier_init(&barrier, NULL, 4) != 0) {
        printf("[-] Failed to init barrier: %s\n", strerror(errno));
        exit(1);
    }

    pthread_t tb, tc, td, te;
    if (pthread_create(&tb, NULL, thread_bc, NULL) != 0 ||
        pthread_create(&tc, NULL, thread_bc, NULL) != 0 ||
        pthread_create(&td, NULL, thread_bc, NULL) != 0 ||
        pthread_create(&te, NULL, thread_bc, NULL) != 0) {
        printf("[-] Failed to create threads: %s\n", strerror(errno));
        exit(1);
    }

    pthread_join(tb, NULL);
    pthread_join(tc, NULL);
    pthread_join(td, NULL);
    pthread_join(te, NULL);
    printf("[+] Phase 2 completed.\n");

    if (umount("merged") != 0) {
        printf("[-] Failed to umount merged: %s\n", strerror(errno));
        exit(1);
    }
    printf("[+] Overlayfs unmounted successfully.\n");

    return 0;
}