In ImageMagick 7.0.8-40 Q16, there is a heap-based buffer over-read in the function WritePNMImage of coders/pnm.c, which allows an attacker to cause a denial of service or possibly information disclosure via a crafted image file. This is related to SetGrayscaleImage in MagickCore/quantize.c.
### Prerequisites

- [X] I have written a descriptive issue title
- [X] I have verified that I am using the latest version of ImageMagick
- [X] I have searched [open](https://github.com/ImageMagick/ImageMagick/issues) and [closed](https://github.com/ImageMagick/ImageMagick/issues?q=is%3Aissue+is%3Aclosed) issues to ensure it has not already been reported

### Description
<!-- A description of the bug or feature -->
There is a heap buffer overflow vulnerability in function WritePNMImage of coders/pnm.c.
### Steps to Reproduce
<!-- List of steps, sample code, failing test or link to a project that reproduces the behavior.
     Make sure you place a stack trace inside a code (```) block to avoid linking unrelated issues -->
[poc](https://drive.google.com/open?id=14WjaSf3CMM-h6HnuQ1xufVGkC_swvJma)
magick convert $poc ./test.pnm
`=================================================================`
`==16178==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60200000b6f0 at pc 0x0000009f987d bp 0x7fff206e34b0 sp 0x7fff206e34a0`
`READ of size 8 at 0x60200000b6f0 thread T0`
`==16178==AddressSanitizer: while reporting a bug found another one. Ignoring.`
`    #0 0x9f987c in SetGrayscaleImage._omp_fn.4 MagickCore/quantize.c:3453`
`    #1 0x7f12195becbe in GOMP_parallel (/usr/lib/x86_64-linux-gnu/libgomp.so.1+0xbcbe)`
`    #2 0x9f676d in SetGrayscaleImage MagickCore/quantize.c:3432`
`    #3 0x9f3ee7 in QuantizeImage MagickCore/quantize.c:2677`
`    #4 0x7cf518 in SetImageType MagickCore/attribute.c:1364`
`    #5 0x6766a7 in WritePNMImage coders/pnm.c:1938`
`    #6 0x8485ba in WriteImage MagickCore/constitute.c:1159`
`    #7 0x8492df in WriteImages MagickCore/constitute.c:1376`
`    #8 0xbf05a1 in ConvertImageCommand MagickWand/convert.c:3305`
`    #9 0xcdc6f2 in MagickCommandGenesis MagickWand/mogrify.c:184`
`    #10 0x410091 in MagickMain utilities/magick.c:149`
`    #11 0x410272 in main utilities/magick.c:180`
`    #12 0x7f1218cea82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)`
`    #13 0x40fba8 in _start (/home/ImageMagick/utilities/magick+0x40fba8)`
``
`0x60200000b6f4 is located 0 bytes to the right of 4-byte region [0x60200000b6f0,0x60200000b6f4)`
`allocated by thread T0 here:`
`    #0 0x7f121d489602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602)`
`    #1 0x4408a5 in AcquireMagickMemory MagickCore/memory.c:478`
`    #2 0x4408f9 in AcquireQuantumMemory MagickCore/memory.c:551`
`    #3 0x4c3f69 in ConstantString MagickCore/string.c:713`
`    #4 0x43d3e0 in AcquireMagickInfo MagickCore/magick.c:193`
`    #5 0x6747aa in RegisterPNMImage coders/pnm.c:1456`
`    #6 0x49fc1d in RegisterStaticModule MagickCore/static.c:257`
`    #7 0x43df66 in GetMagickInfo MagickCore/magick.c:642`
`    #8 0x42164a in SetImageInfo MagickCore/image.c:2855`
`    #9 0x849087 in WriteImages MagickCore/constitute.c:1336`
`    #10 0xbf05a1 in ConvertImageCommand MagickWand/convert.c:3305`
`    #11 0xcdc6f2 in MagickCommandGenesis MagickWand/mogrify.c:184`
`    #12 0x410091 in MagickMain utilities/magick.c:149`
`    #13 0x410272 in main utilities/magick.c:180`
`    #14 0x7f1218cea82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)`
``
`SUMMARY: AddressSanitizer: heap-buffer-overflow MagickCore/quantize.c:3453 SetGrayscaleImage._omp_fn.4`
`Shadow bytes around the buggy address:`
`  0x0c047fff9680: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`  0x0c047fff9690: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`  0x0c047fff96a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`  0x0c047fff96b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`  0x0c047fff96c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`=>0x0c047fff96d0: fa fa fa fa fa fa 00 00 fa fa 04 fa fa fa[04]fa`
`  0x0c047fff96e0: fa fa 00 00 fa fa 04 fa fa fa 04 fa fa fa 04 fa`
`  0x0c047fff96f0: fa fa 04 fa fa fa 04 fa fa fa 04 fa fa fa 04 fa`
`  0x0c047fff9700: fa fa 04 fa fa fa 04 fa fa fa 04 fa fa fa 00 04`
`  0x0c047fff9710: fa fa 00 04 fa fa 00 04 fa fa 00 04 fa fa 00 04`
`  0x0c047fff9720: fa fa 00 04 fa fa 00 04 fa fa 00 04 fa fa 00 04`
`Shadow byte legend (one shadow byte represents 8 application bytes):`
`  Addressable:           00`
`  Partially addressable: 01 02 03 04 05 06 07 `
`  Heap left redzone:       fa`
`  Heap right redzone:      fb`
`  Freed heap region:       fd`
`  Stack left redzone:      f1`
`  Stack mid redzone:       f2`
`  Stack right redzone:     f3`
`  Stack partial redzone:   f4`
`  Stack after return:      f5`
`  Stack use after scope:   f8`
`  Global redzone:          f9`
`  Global init order:       f6`
`  Poisoned by user:        f7`
`  Container overflow:      fc`
`  Array cookie:            ac`
`  Intra object redzone:    bb`
`  ASan internal:           fe`
`==16178==ABORTING`
### System Configuration
<!-- Tell us about the environment where you are experiencing the bug -->

- ImageMagick version:
```
Version: ImageMagick 7.0.8-40 Q16 x86_64 2019-04-08 https://imagemagick.org
Copyright: ? 1999-2019 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC HDRI OpenMP 
Delegates (built-in): bzlib djvu fftw fontconfig freetype jbig jng jpeg lcms lqr lzma openexr pangocairo png tiff wmf x xml zlib
```
- Environment (Operating system, version and so on):
```
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.1 LTS
Release:	16.04
Codename:	xenial
```
- Additional information:

<!-- Thanks for reporting the issue to ImageMagick! -->

heap-buffer-overflow in WritePNMImage of coders/pnm.c
This is a GitHub Issue
repo:ImageMagick
owner:ImageMagick
Title : heap-buffer-overflow in WritePNMImage of coders/pnm.c
Issue date:

--- start body ---
### Prerequisites

- [X] I have written a descriptive issue title
- [X] I have verified that I am using the latest version of ImageMagick
- [X] I have searched [open](https://github.com/ImageMagick/ImageMagick/issues) and [closed](https://github.com/ImageMagick/ImageMagick/issues?q=is%3Aissue+is%3Aclosed) issues to ensure it has not already been reported

### Description
<!-- A description of the bug or feature -->
There is a heap buffer overflow vulnerability in function WritePNMImage of coders/pnm.c.
### Steps to Reproduce
<!-- List of steps, sample code, failing test or link to a project that reproduces the behavior.
     Make sure you place a stack trace inside a code (```) block to avoid linking unrelated issues -->
[poc](https://drive.google.com/open?id=14WjaSf3CMM-h6HnuQ1xufVGkC_swvJma)
magick convert $poc ./test.pnm
`=================================================================`
`==16178==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60200000b6f0 at pc 0x0000009f987d bp 0x7fff206e34b0 sp 0x7fff206e34a0`
`READ of size 8 at 0x60200000b6f0 thread T0`
`==16178==AddressSanitizer: while reporting a bug found another one. Ignoring.`
`    #0 0x9f987c in SetGrayscaleImage._omp_fn.4 MagickCore/quantize.c:3453`
`    #1 0x7f12195becbe in GOMP_parallel (/usr/lib/x86_64-linux-gnu/libgomp.so.1+0xbcbe)`
`    #2 0x9f676d in SetGrayscaleImage MagickCore/quantize.c:3432`
`    #3 0x9f3ee7 in QuantizeImage MagickCore/quantize.c:2677`
`    #4 0x7cf518 in SetImageType MagickCore/attribute.c:1364`
`    #5 0x6766a7 in WritePNMImage coders/pnm.c:1938`
`    #6 0x8485ba in WriteImage MagickCore/constitute.c:1159`
`    #7 0x8492df in WriteImages MagickCore/constitute.c:1376`
`    #8 0xbf05a1 in ConvertImageCommand MagickWand/convert.c:3305`
`    #9 0xcdc6f2 in MagickCommandGenesis MagickWand/mogrify.c:184`
`    #10 0x410091 in MagickMain utilities/magick.c:149`
`    #11 0x410272 in main utilities/magick.c:180`
`    #12 0x7f1218cea82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)`
`    #13 0x40fba8 in _start (/home/ImageMagick/utilities/magick+0x40fba8)`
``
`0x60200000b6f4 is located 0 bytes to the right of 4-byte region [0x60200000b6f0,0x60200000b6f4)`
`allocated by thread T0 here:`
`    #0 0x7f121d489602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602)`
`    #1 0x4408a5 in AcquireMagickMemory MagickCore/memory.c:478`
`    #2 0x4408f9 in AcquireQuantumMemory MagickCore/memory.c:551`
`    #3 0x4c3f69 in ConstantString MagickCore/string.c:713`
`    #4 0x43d3e0 in AcquireMagickInfo MagickCore/magick.c:193`
`    #5 0x6747aa in RegisterPNMImage coders/pnm.c:1456`
`    #6 0x49fc1d in RegisterStaticModule MagickCore/static.c:257`
`    #7 0x43df66 in GetMagickInfo MagickCore/magick.c:642`
`    #8 0x42164a in SetImageInfo MagickCore/image.c:2855`
`    #9 0x849087 in WriteImages MagickCore/constitute.c:1336`
`    #10 0xbf05a1 in ConvertImageCommand MagickWand/convert.c:3305`
`    #11 0xcdc6f2 in MagickCommandGenesis MagickWand/mogrify.c:184`
`    #12 0x410091 in MagickMain utilities/magick.c:149`
`    #13 0x410272 in main utilities/magick.c:180`
`    #14 0x7f1218cea82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)`
``
`SUMMARY: AddressSanitizer: heap-buffer-overflow MagickCore/quantize.c:3453 SetGrayscaleImage._omp_fn.4`
`Shadow bytes around the buggy address:`
`  0x0c047fff9680: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`  0x0c047fff9690: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`  0x0c047fff96a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`  0x0c047fff96b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`  0x0c047fff96c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa`
`=>0x0c047fff96d0: fa fa fa fa fa fa 00 00 fa fa 04 fa fa fa[04]fa`
`  0x0c047fff96e0: fa fa 00 00 fa fa 04 fa fa fa 04 fa fa fa 04 fa`
`  0x0c047fff96f0: fa fa 04 fa fa fa 04 fa fa fa 04 fa fa fa 04 fa`
`  0x0c047fff9700: fa fa 04 fa fa fa 04 fa fa fa 04 fa fa fa 00 04`
`  0x0c047fff9710: fa fa 00 04 fa fa 00 04 fa fa 00 04 fa fa 00 04`
`  0x0c047fff9720: fa fa 00 04 fa fa 00 04 fa fa 00 04 fa fa 00 04`
`Shadow byte legend (one shadow byte represents 8 application bytes):`
`  Addressable:           00`
`  Partially addressable: 01 02 03 04 05 06 07 `
`  Heap left redzone:       fa`
`  Heap right redzone:      fb`
`  Freed heap region:       fd`
`  Stack left redzone:      f1`
`  Stack mid redzone:       f2`
`  Stack right redzone:     f3`
`  Stack partial redzone:   f4`
`  Stack after return:      f5`
`  Stack use after scope:   f8`
`  Global redzone:          f9`
`  Global init order:       f6`
`  Poisoned by user:        f7`
`  Container overflow:      fc`
`  Array cookie:            ac`
`  Intra object redzone:    bb`
`  ASan internal:           fe`
`==16178==ABORTING`
### System Configuration
<!-- Tell us about the environment where you are experiencing the bug -->

- ImageMagick version:
```
Version: ImageMagick 7.0.8-40 Q16 x86_64 2019-04-08 https://imagemagick.org
Copyright: ? 1999-2019 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC HDRI OpenMP 
Delegates (built-in): bzlib djvu fftw fontconfig freetype jbig jng jpeg lcms lqr lzma openexr pangocairo png tiff wmf x xml zlib
```
- Environment (Operating system, version and so on):
```
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.1 LTS
Release:	16.04
Codename:	xenial
```
- Additional information:

<!-- Thanks for reporting the issue to ImageMagick! -->

--- end body ---
