Re: KMSAN: uninit-value in __dev_mc_add

[Vladis Dronov]

Hello,

This report is actually for the same bug which was reported in:

https://syzkaller.appspot.com/bug?id=088efeac32fdde781038a777a63e436c0d4d7036

The note there that the bug was fixed by "Commits: net: fix uninit-value in
__hw_addr_add_ex()" is wrong. A C-reproducer from the 2nd syzkaller report
can trigger the bug from this one.

I've researched this and a result is a proposed patch, the problem is the tun
device code allowing to set an arbitrary link type.

https://lkml.org/lkml/2018/9/26/416
https://lore.kernel.org/lkml/20180926093018.6646-1-vdro...@redhat.com/T/#u
https://marc.info/?l=linux-netdev&m=153795423320016&w=2

A simplified reproducer is attached.

Best regards,
Vladis Dronov

#define _GNU_SOURCE
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/futex.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <unistd.h>

#include <errno.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char **argv)
{
  int ret, sockfd, tunfd;

  syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);

  // socket(AF_PACKET, SOCK_DGRAM|SOCK_NONBLOCK, 0)
  sockfd = syscall(__NR_socket, 0x11, 0x100000802, 0);
  if (sockfd < 0) {
    perror("socket()");
    ret = 1;
    goto exit_end;
  }

  memcpy((void*)0x20000240, "/dev/net/tun", 13);
  tunfd = open((char *)0x20000240, 0);
  if (tunfd < 0) {
    perror("open()");
    ret = 2;
    goto exit_sock_close;
  }

  memcpy((void*)0x200000c0, 
"\x69\x67\x62\x30\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", 16);
  *(uint16_t*)0x200000d0 = 0x4012;
  ret = syscall(__NR_ioctl, tunfd, 0x400454ca, 0x200000c0); // TUNSETIFF 
_IOW('T', 202, int)
  if (ret < 0) {
    perror("ioctl(TUNSETIFF)");
    ret = 3;
    goto exit_tun_close;
  }

  // TUNSETLINK _IOW('T', 205, int) / 0x30a = 778 = ARPHRD_IPGRE
  if (argc < 2)
    ret = syscall(__NR_ioctl, tunfd, 0x400454cd, 0x30a);
  else
    ret = syscall(__NR_ioctl, tunfd, 0x400454cd, atoi(argv[1]));
  if (ret < 0) {
    perror("ioctl(TUNSETLINK)");
    ret = 4;
    goto exit_tun_close;
  }

  memcpy((void*)0x20000040, 
"\x69\x67\x62\x30\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", 16);
  *(uint16_t*)0x20000050 = 0xa201;
  ret = syscall(__NR_ioctl, sockfd, 0x8914, 0x20000040); // SIOCSIFFLAGS 0x8914
  if (ret < 0) {
    perror("ioctl(SIOCSIFFLAGS)");
    ret = 5;
    goto exit_tun_close;
  }

  printf("done:\n");
  system("/usr/sbin/ip -details link show igb0");

exit_tun_close:
  close(tunfd);
exit_sock_close:
  close(sockfd);
exit_end:
  munmap((void *)0x20000000, 0x1000000);
  return 0;
}