[UBSAN Bug report]: signed integer overflow in UB in yura_hash of fs/reiserfs/hashes.c

[Changming Liu <liu.changm@xxxxxxxxxxxxxxxx>]

Hi Folks,

I'm a PhD student interested in testing kernel with UBSan,
syzkaller reported this UBSan report on function yura_hash in fs/reiserfs/hashes.c:135.

>From brief manual validation, the result of this signed-overflow is undefined.

If I remember correctly, it is said that all signed overflow in the kernel
module are essentially wrap-arounds, rather than being undefined.
I'm wondering does it apply to this case?

This will help me understand linux and UB a lot, any feedback is greatly appreciated.

===============================================================================
REISERFS (device loop0): checking transaction log (loop0)
REISERFS (device loop0): Using rupasov hash to sort names
================================================================================
UBSAN: Undefined behaviour in fs/reiserfs/hashes.c:135:7
signed integer overflow:
1000000000 * 10 cannot be represented in type 'int'
CPU: 0 PID: 10804 Comm: syz-executor.0 Not tainted 5.4.0+ #27
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0xc6/0x11e lib/dump_stack.c:118
 ubsan_epilogue+0xe/0x40 lib/ubsan.c:158
 handle_overflow+0xdf/0xf0 lib/ubsan.c:189
 yura_hash+0x266/0x2e0 fs/reiserfs/hashes.c:135
 get_third_component+0x97/0x1b0 fs/reiserfs/namei.c:195
 reiserfs_find_entry.part.4+0xc9/0x13b0 fs/reiserfs/namei.c:316
 reiserfs_find_entry fs/reiserfs/namei.c:367 [inline]
 reiserfs_lookup+0x238/0x410 fs/reiserfs/namei.c:366
 __lookup_slow+0x217/0x410 fs/namei.c:1663
 lookup_one_len+0x150/0x180 fs/namei.c:2533
 reiserfs_lookup_privroot+0x90/0x230 fs/reiserfs/xattr.c:964
 reiserfs_fill_super+0x1dc7/0x2540 fs/reiserfs/super.c:2173
 mount_bdev+0x2aa/0x360 fs/super.c:1415
 legacy_get_tree+0x103/0x200 fs/fs_context.c:647
 vfs_get_tree+0x86/0x340 fs/super.c:1545
 do_new_mount fs/namespace.c:2822 [inline]
 do_mount+0x109a/0x1730 fs/namespace.c:3142
 ksys_mount+0xa8/0x120 fs/namespace.c:3351
 __do_sys_mount fs/namespace.c:3365 [inline]
 __se_sys_mount fs/namespace.c:3362 [inline]
 __x64_sys_mount+0xba/0x150 fs/namespace.c:3362
 do_syscall_64+0x9d/0x5a0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4608aa
Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 ad 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 8a 89 fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007f167680ca88 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f167680cb20 RCX: 00000000004608aa
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f167680cae0
RBP: 00007f167680cae0 R08: 00007f167680cb20 R09: 0000000020000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000020000000
R13: 0000000020000100 R14: 0000000020000200 R15: 0000000020011500
================================================================================
================================================================================




C reproducer:
// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE

#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

#include <linux/loop.h>

static unsigned long long procid;

struct fs_image_segment {
  void* data;
  uintptr_t size;
  uintptr_t offset;
};

#define IMAGE_MAX_SEGMENTS 4096
#define IMAGE_MAX_SIZE (129 << 20)

#define sys_memfd_create 319

static unsigned long fs_image_segment_check(unsigned long size,
                                            unsigned long nsegs,
                                            struct fs_image_segment* segs)
{
  if (nsegs > IMAGE_MAX_SEGMENTS)
    nsegs = IMAGE_MAX_SEGMENTS;
  for (size_t i = 0; i < nsegs; i++) {
    if (segs[i].size > IMAGE_MAX_SIZE)
      segs[i].size = IMAGE_MAX_SIZE;
    segs[i].offset %= IMAGE_MAX_SIZE;
    if (segs[i].offset > IMAGE_MAX_SIZE - segs[i].size)
      segs[i].offset = IMAGE_MAX_SIZE - segs[i].size;
    if (size < segs[i].offset + segs[i].offset)
      size = segs[i].offset + segs[i].offset;
  }
  if (size > IMAGE_MAX_SIZE)
    size = IMAGE_MAX_SIZE;
  return size;
}
static int setup_loop_device(long unsigned size, long unsigned nsegs,
                             struct fs_image_segment* segs,
                             const char* loopname, int* memfd_p, int* loopfd_p)
{
  int err = 0, loopfd = -1;
  size = fs_image_segment_check(size, nsegs, segs);
  int memfd = syscall(sys_memfd_create, "syzkaller", 0);
  if (memfd == -1) {
    err = errno;
    goto error;
  }
  if (ftruncate(memfd, size)) {
    err = errno;
    goto error_close_memfd;
  }
  for (size_t i = 0; i < nsegs; i++) {
    if (pwrite(memfd, segs[i].data, segs[i].size, segs[i].offset) < 0) {
    }
  }
  loopfd = open(loopname, O_RDWR);
  if (loopfd == -1) {
    err = errno;
    goto error_close_memfd;
  }
  if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
    if (errno != EBUSY) {
      err = errno;
      goto error_close_loop;
    }
    ioctl(loopfd, LOOP_CLR_FD, 0);
    usleep(1000);
    if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
      err = errno;
      goto error_close_loop;
    }
  }
  *memfd_p = memfd;
  *loopfd_p = loopfd;
  return 0;

error_close_loop:
  close(loopfd);
error_close_memfd:
  close(memfd);
error:
  errno = err;
  return -1;
}

static long syz_mount_image(volatile long fsarg, volatile long dir,
                            volatile unsigned long size,
                            volatile unsigned long nsegs,
                            volatile long segments, volatile long flags,
                            volatile long optsarg)
{
  struct fs_image_segment* segs = (struct fs_image_segment*)segments;
  int res = -1, err = 0, loopfd = -1, memfd = -1, need_loop_device = !!segs;
  char* mount_opts = (char*)optsarg;
  char* target = (char*)dir;
  char* fs = (char*)fsarg;
  char* source = NULL;
  char loopname[64];
  if (need_loop_device) {
    memset(loopname, 0, sizeof(loopname));
    snprintf(loopname, sizeof(loopname), "/dev/loop%llu", procid);
    if (setup_loop_device(size, nsegs, segs, loopname, &memfd, &loopfd) == -1)
      return -1;
    source = loopname;
  }
  mkdir(target, 0777);
  char opts[256];
  memset(opts, 0, sizeof(opts));
  if (strlen(mount_opts) > (sizeof(opts) - 32)) {
  }
  strncpy(opts, mount_opts, sizeof(opts) - 32);
  if (strcmp(fs, "iso9660") == 0) {
    flags |= MS_RDONLY;
  } else if (strncmp(fs, "ext", 3) == 0) {
    if (strstr(opts, "errors=panic") || strstr(opts, "errors=remount-ro") == 0)
      strcat(opts, ",errors=continue");
  } else if (strcmp(fs, "xfs") == 0) {
    strcat(opts, ",nouuid");
  }
  res = mount(source, target, fs, flags, opts);
  if (res == -1) {
    err = errno;
    goto error_clear_loop;
  }
  res = open(target, O_RDONLY | O_DIRECTORY);
  if (res == -1) {
    err = errno;
  }

error_clear_loop:
  if (need_loop_device) {
    ioctl(loopfd, LOOP_CLR_FD, 0);
    close(loopfd);
    close(memfd);
  }
  errno = err;
  return res;
}

int main(void)
{
  syscall(__NR_mmap, 0x1ffff000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
  syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul);
  syscall(__NR_mmap, 0x21000000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);

  memcpy((void*)0x20000000, "reiserfs\000", 9);
  memcpy((void*)0x20000100, "./file0\000", 8);
  *(uint64_t*)0x20000200 = 0x20010000;
  memcpy((void*)0x20010000,
         "\x00\x04\x00\x00\xec\x01\x00\x00\x13\x02\x00\x00\x12\x00\x00\x00\x00"
         "\x00\x00\x00\x00\x02\x00\x00\x00\x01\x00\x00\x61\x1c\xad\x49\xe1\x00"
         "\x00\x00\x1e\x00\x00\x00\x00\x00\x00\x00\x00\x10\xcc\x03\x02\x00\x01"
         "\x00\x52\x65\x49\x73\x45\x72\x33\x46\x73\x00\x00\x00\x02\x00\x00\x00"
         "\x02\x00\x01\x00\x02\x00\x01\x02\x00\x00\x00\x00\x01\x00\x00\x00\x12"
         "\x31\x23\x12\x12\x33\x12\x33\x12\x31\x12\x34\x13\x41\x24\x12\x73\x79"
         "\x7a\x6b\x61\x6c\x6c\x65\x72\x00\x00\x00\x00\x00\x00\x00\x01\x00\x1e"
         "\x00\x3a\xc1\x65\x5f\x00\x4e\xed\x00",
         128);
  *(uint64_t*)0x20000208 = 0x80;
  *(uint64_t*)0x20000210 = 0x10000;
  *(uint64_t*)0x20000218 = 0;
  *(uint64_t*)0x20000220 = 0;
  *(uint64_t*)0x20000228 = 0x100c0;
  *(uint64_t*)0x20000230 = 0;
  *(uint64_t*)0x20000238 = 0;
  *(uint64_t*)0x20000240 = 0x11000;
  *(uint64_t*)0x20000248 = 0x20011200;
  memcpy((void*)0x20011200,
         "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x12\x00\x00\x00\x00"
         "\x00\x00\x00\x00\x02\x00\x00\x00\x01\x00\x00\x61\x1c\xad\x49\xe1\x00"
         "\x00\x00\x1e\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
         "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
         64);
  *(uint64_t*)0x20000250 = 0x40;
  *(uint64_t*)0x20000258 = 0x212000;
  *(uint64_t*)0x20000260 = 0x20011300;
  memcpy((void*)0x20011300,
         "\x01\x00\x02\x00\x5c\x0f\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
         "\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x02\x00\x00\x00\x00\x00"
         "\x00\x00\x00\x00\x00\x00\x00\x00\x2c\x00\xd4\x0f\x01\x00\x01\x00\x00"
         "\x00\x02\x00\x00\x00\x01\x00\x00\x00\xf4\x01\x00\x00\x02\x00\x30\x00"
         "\xa4\x0f\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
         "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
         96);
  *(uint64_t*)0x20000268 = 0x60;
  *(uint64_t*)0x20000270 = 0x213000;
  *(uint64_t*)0x20000278 = 0x20011400;
  memcpy((void*)0x20011400,
         "\x00\x00\x00\x00\x01\x00\x00\x00\x01\x00\x00\x00\x02\x00\x00\x00\x28"
         "\x00\x04\x00\x02\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x20\x00"
         "\x04\x00\x2e\x2e\x00\x00\x00\x00\x00\x00\x2e\x00\x00\x00\x00\x00\x00"
         "\x00\xed\x41\x00\x00\x03\x00\x00\x00\x30\x00\x00\x00\x00\x00\x00\x00"
         "\x5c\xf9\x01\x00\x53\x5f\x01\x00\x3a\xc1\x65\x5f\x3a\xc1\x65\x5f\x3a"
         "\xc1\x65\x5f\x01\x00\x00\x00\x00\x00\x00\x00",
         96);
  *(uint64_t*)0x20000280 = 0x60;
  *(uint64_t*)0x20000288 = 0x213fa0;
  *(uint8_t*)0x20011500 = 0;
  syz_mount_image(0x20000000, 0x20000100, 0x400000, 6, 0x20000200, 0,
                  0x20011500);
  return 0;
}



Best,
Changming Liu