Re: divide error in mb_update_avg_fragment_size

[xingwei lee]

Hello I saw you can't reproduce this bug and I reproduce it with
repro.c and repro.txt
I test the repro.c in the lastest HEAD: 5e3f5b81de80c98338bcb47c233aebefee5a4801
kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=6ae1a4ee971a7305
and the bug also existed.

=* repro.c =*
// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/prctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

static unsigned long long procid;

static void sleep_ms(uint64_t ms) { usleep(ms * 1000); }

static uint64_t current_time_ms(void) {
  struct timespec ts;
  if (clock_gettime(CLOCK_MONOTONIC, &ts)) exit(1);
  return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
}

static bool write_file(const char* file, const char* what, ...) {
  char buf[1024];
  va_list args;
  va_start(args, what);
  vsnprintf(buf, sizeof(buf), what, args);
  va_end(args);
  buf[sizeof(buf) - 1] = 0;
  int len = strlen(buf);
  int fd = open(file, O_WRONLY | O_CLOEXEC);
  if (fd == -1) return false;
  if (write(fd, buf, len) != len) {
    int err = errno;
    close(fd);
    errno = err;
    return false;
  }
  close(fd);
  return true;
}

static void kill_and_wait(int pid, int* status) {
  kill(-pid, SIGKILL);
  kill(pid, SIGKILL);
  for (int i = 0; i < 100; i++) {
    if (waitpid(-1, status, WNOHANG | __WALL) == pid) return;
    usleep(1000);
  }
  DIR* dir = opendir("/sys/fs/fuse/connections");
  if (dir) {
    for (;;) {
      struct dirent* ent = readdir(dir);
      if (!ent) break;
      if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0)
        continue;
      char abort[300];
      snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort",
               ent->d_name);
      int fd = open(abort, O_WRONLY);
      if (fd == -1) {
        continue;
      }
      if (write(fd, abort, 1) < 0) {
      }
      close(fd);
    }
    closedir(dir);
  } else {
  }
  while (waitpid(-1, status, __WALL) != pid) {
  }
}

static void setup_test() {
  prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
  setpgrp();
  write_file("/proc/self/oom_score_adj", "1000");
}

static void execute_one(void);

#define WAIT_FLAGS __WALL

static void loop(void) {
  int iter = 0;
  for (;; iter++) {
    int pid = fork();
    if (pid < 0) exit(1);
    if (pid == 0) {
      setup_test();
      execute_one();
      exit(0);
    }
    int status = 0;
    uint64_t start = current_time_ms();
    for (;;) {
      if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid) break;
      sleep_ms(1);
      if (current_time_ms() - start < 5000) continue;
      kill_and_wait(pid, &status);
      break;
    }
  }
}

uint64_t r[5] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff,
                 0xffffffffffffffff, 0xffffffffffffffff};

void execute_one(void) {
  intptr_t res = 0;
  memcpy((void*)0x20000280, "cgroup.controllers\000", 19);
  res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x20000280ul,
                /*flags=*/0x275aul, /*mode=*/0ul);
  if (res != -1) r[0] = res;
  memcpy((void*)0x20000180, "cgroup.controllers\000", 19);
  res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x20000180ul,
                /*flags=*/0x275aul, /*mode=*/0ul);
  if (res != -1) r[1] = res;
  res = syscall(__NR_dup3, /*oldfd=*/r[1], /*newfd=*/r[0], /*flags=*/0ul);
  if (res != -1) r[2] = res;
  *(uint32_t*)0x20000140 = 0x20;
  *(uint32_t*)0x20000144 = 0x8c8c;
  *(uint32_t*)0x20000148 = 0;
  *(uint32_t*)0x2000014c = 0;
  *(uint32_t*)0x20000150 = 0;
  memset((void*)0x20000154, 0, 8);
  syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0x401c5820, /*arg=*/0x20000140ul);
  sprintf((char*)0x20000040, "0x%016llx", (long long)0);
  syscall(__NR_write, /*fd=*/r[0], /*buf=*/0x20000040ul, /*len=*/0xfea0ul);
  memcpy((void*)0x200001c0, "cpuset.effective_cpus\000", 22);
  res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x200001c0ul,
                /*flags=*/0x275aul, /*mode=*/0ul);
  if (res != -1) r[3] = res;
  sprintf((char*)0x20000380, "0x%016llx", (long long)0);
  syscall(__NR_write, /*fd=*/r[3], /*buf=*/0x20000380ul, /*len=*/0x101bful);
  syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x660c, 0);
  *(uint32_t*)0x200000c0 = 0;
  *(uint32_t*)0x200000c4 = r[3];
  *(uint64_t*)0x200000c8 = 7;
  *(uint64_t*)0x200000d0 = 0;
  *(uint64_t*)0x200000d8 = 0;
  *(uint64_t*)0x200000e0 = 0;
  syscall(__NR_ioctl, /*fd=*/r[2], /*cmd=*/0xc028660f, /*arg=*/0x200000c0ul);
  syscall(__NR_writev, /*fd=*/-1, /*vec=*/0ul, /*vlen=*/0ul);
  syscall(__NR_ioctl, /*fd=*/-1, /*cmd=*/0x40045569, /*arg=*/9ul);
  syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0ul, /*flags=*/0x275aul,
          /*mode=*/0ul);
  memcpy((void*)0x20000180, "cgroup.controllers\000", 19);
  res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x20000180ul,
                /*flags=*/0x275aul, /*mode=*/0ul);
  if (res != -1) r[4] = res;
  *(uint64_t*)0x200000c0 = 4;
  *(uint64_t*)0x200000c8 = 0x16000000000000;
  *(uint64_t*)0x200000d0 = 0x20;
  syscall(__NR_ioctl, /*fd=*/r[4], /*cmd=*/0xc0185879, /*arg=*/0x200000c0ul);
}
int main(void) {
  syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul,
          /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
  syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul, /*prot=*/7ul,
          /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
  syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul,
          /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
  for (procid = 0; procid < 4; procid++) {
    if (fork() == 0) {
      loop();
    }
  }
  sleep(1000000);
  return 0;
}

=* repro.txt =*
r0 = openat$cgroup_ro(0xffffffffffffff9c,
&(0x7f0000000280)='cgroup.controllers\x00', 0x275a, 0x0)
r1 = openat$cgroup_ro(0xffffffffffffff9c,
&(0x7f0000000180)='cgroup.controllers\x00', 0x275a, 0x0)
r2 = dup3(r1, r0, 0x0)
ioctl$FS_IOC_FSSETXATTR(r0, 0x401c5820, &(0x7f0000000140)={0x20, 0x8c8c})
write$cgroup_int(r0, &(0x7f0000000040), 0xfea0)
r3 = openat$cgroup_ro(0xffffffffffffff9c,
&(0x7f00000001c0)='cpuset.effective_cpus\x00', 0x275a, 0x0)
write$cgroup_int(r3, &(0x7f0000000380), 0x101bf)
ioctl$EXT4_IOC_ALLOC_DA_BLKS(r3, 0x660c)
ioctl$EXT4_IOC_MOVE_EXT(r2, 0xc028660f, &(0x7f00000000c0)={0x0, r3, 0x7})
writev(0xffffffffffffffff, 0x0, 0x0)
ioctl$UI_SET_LEDBIT(0xffffffffffffffff, 0x40045569, 0x9)
openat$cgroup_ro(0xffffffffffffff9c, 0x0, 0x275a, 0x0)
r4 = openat$cgroup_ro(0xffffffffffffff9c,
&(0x7f0000000180)='cgroup.controllers\x00', 0x275a, 0x0)
ioctl$FITRIM(r4, 0xc0185879, &(0x7f00000000c0)={0x4, 0x16000000000000, 0x20})

and also https://gist.github.com/xrivendell7/bad992c2b716ed14310efa2c6f878b7c