A call to ConformPixelInfo() in the SetImageAlphaChannel() routine of /MagickCore/channel.c caused a subsequent heap-use-after-free or heap-buffer-overflow READ when GetPixelRed() or GetPixelBlue() was called. This could occur if an attacker is able to submit a malicious image file to be processed by ImageMagick and could lead to denial of service. It likely would not lead to anything further because the memory is used as pixel data and not e.g. a function pointer. This flaw affects ImageMagick versions prior to 7.0.9-0.
### 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-use-after-free at MagickCore/pixel-accessor.h:378:10 in GetPixelRed
### 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/file/d/1liJ7nJK0A4M_us-LuLZjwmqKXukx3nbO/view?usp=sharing)
please run a following cmd with poc file.
`magick $PoC -despeckle -flip -monochrome -alpha Shape tmp.rla`

Here's ASAN log.
```
==8370==ERROR: AddressSanitizer: heap-use-after-free on address 0x62a000024200 at pc 0x000000796779 bp 0x7ffdf7956b10 sp 0x7ffdf7956b08
READ of size 4 at 0x62a000024200 thread T0
    #0 0x796778 in GetPixelRed ImageMagick/./MagickCore/pixel-accessor.h:378:10
    #1 0x7938d7 in GetPixelIntensity ImageMagick/MagickCore/pixel.c:2367:24
    #2 0x258de7a in SetImageAlphaChannel ImageMagick/MagickCore/channel.c:1298:28
    #3 0x625776b in CLISimpleOperatorImage ImageMagick/MagickWand/operation.c:1765:18
    #4 0x6250c70 in CLISimpleOperatorImages ImageMagick/MagickWand/operation.c:3685:12
    #5 0x632eddb in CLIOption ImageMagick/MagickWand/operation.c:5302:16
    #6 0x5588f52 in ProcessCommandOptions ImageMagick/MagickWand/magick-cli.c:477:7
    #7 0x55910cc in MagickImageCommand ImageMagick/MagickWand/magick-cli.c:796:5
    #8 0x559b0e3 in MagickCommandGenesis ImageMagick/MagickWand/mogrify.c:185:14
    #9 0x51c3e5 in MagickMain ImageMagick/utilities/magick.c:149:10
    #10 0x519c69 in main ImageMagick/utilities/magick.c:180:10
    #11 0x7fdc4a357b96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310
    #12 0x421849 in _start (magick+0x421849)

0x62a000024200 is located 0 bytes inside of 22592-byte region [0x62a000024200,0x62a000029a40)
freed by thread T0 here:
    #0 0x4e1530 in __interceptor_free.localalias.0 (magick+0x4e1530)
    #1 0x6c76f0 in RelinquishAlignedMemory ImageMagick/MagickCore/memory.c:1037:3
    #2 0x245efb2 in RelinquishPixelCachePixels ImageMagick/MagickCore/cache.c:974:40
    #3 0x24e304f in OpenPixelCache ImageMagick/MagickCore/cache.c:3762:19
    #4 0x2506bd7 in GetImagePixelCache ImageMagick/MagickCore/cache.c:1757:18
    #5 0x2533d59 in SyncImagePixelCache ImageMagick/MagickCore/cache.c:5501:28
    #6 0x2601f04 in SetImageColorspace ImageMagick/MagickCore/colorspace.c:1244:10
    #7 0x2609fa7 in TransformsRGBImage ImageMagick/MagickCore/colorspace.c:1981:11
    #8 0x2605cc8 in TransformImageColorspace ImageMagick/MagickCore/colorspace.c:1407:12
    #9 0x70c801 in ConformPixelInfo ImageMagick/MagickCore/pixel.c:232:12
    #10 0x258da15 in SetImageAlphaChannel ImageMagick/MagickCore/channel.c:1294:9
    #11 0x625776b in CLISimpleOperatorImage ImageMagick/MagickWand/operation.c:1765:18
    #12 0x6250c70 in CLISimpleOperatorImages ImageMagick/MagickWand/operation.c:3685:12
    #13 0x632eddb in CLIOption ImageMagick/MagickWand/operation.c:5302:16
    #14 0x5588f52 in ProcessCommandOptions ImageMagick/MagickWand/magick-cli.c:477:7
    #15 0x55910cc in MagickImageCommand ImageMagick/MagickWand/magick-cli.c:796:5
    #16 0x559b0e3 in MagickCommandGenesis ImageMagick/MagickWand/mogrify.c:185:14
    #17 0x51c3e5 in MagickMain ImageMagick/utilities/magick.c:149:10
    #18 0x519c69 in main ImageMagick/utilities/magick.c:180:10
    #19 0x7fdc4a357b96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310

previously allocated by thread T0 here:
    #0 0x4e2338 in __interceptor_posix_memalign (magick+0x4e2338)
    #1 0x6bcd6a in AcquireAlignedMemory ImageMagick/MagickCore/memory.c:265:7
    #2 0x24e0cbd in OpenPixelCache ImageMagick/MagickCore/cache.c:3733:46
    #3 0x2506bd7 in GetImagePixelCache ImageMagick/MagickCore/cache.c:1757:18
    #4 0x2533d59 in SyncImagePixelCache ImageMagick/MagickCore/cache.c:5501:28
    #5 0x56d7ad in SetImageStorageClass ImageMagick/MagickCore/image.c:2625:10
    #6 0x258d244 in SetImageAlphaChannel ImageMagick/MagickCore/channel.c:1266:14
    #7 0x625776b in CLISimpleOperatorImage ImageMagick/MagickWand/operation.c:1765:18
    #8 0x6250c70 in CLISimpleOperatorImages ImageMagick/MagickWand/operation.c:3685:12
    #9 0x632eddb in CLIOption ImageMagick/MagickWand/operation.c:5302:16
    #10 0x5588f52 in ProcessCommandOptions ImageMagick/MagickWand/magick-cli.c:477:7
    #11 0x55910cc in MagickImageCommand ImageMagick/MagickWand/magick-cli.c:796:5
    #12 0x559b0e3 in MagickCommandGenesis ImageMagick/MagickWand/mogrify.c:185:14
    #13 0x51c3e5 in MagickMain ImageMagick/utilities/magick.c:149:10
    #14 0x519c69 in main ImageMagick/utilities/magick.c:180:10
    #15 0x7fdc4a357b96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310

SUMMARY: AddressSanitizer: heap-use-after-free ImageMagick/./MagickCore/pixel-accessor.h:378:10 in GetPixelRed
Shadow bytes around the buggy address:
  0x0c547fffc7f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c547fffc800: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c547fffc810: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c547fffc820: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c547fffc830: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c547fffc840:[fd]fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc850: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc860: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc870: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc880: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc890: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
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
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  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
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==8370==ABORTING

```
### System Configuration
<!-- Tell us about the environment where you are experiencing the bug -->

- ImageMagick version:
Version: ImageMagick 7.0.8-68 Q16 x86_64 2019-10-06 https://imagemagick.org
- Environment (Operating system, version and so on):
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic

- Additional information:
CC=clang-6 CXX=clang++6 CFLAGS="-fsanitize=address,undefined -g" CXXFLAGS="-fsanitize=address,undefined -g" ./configure --disable-openmp


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

heap-use-after-free at MagickCore/pixel-accessor.h in GetPixelRed
This is a GitHub Issue
repo:ImageMagick
owner:ImageMagick
Title : heap-use-after-free at MagickCore/pixel-accessor.h in GetPixelRed
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-use-after-free at MagickCore/pixel-accessor.h:378:10 in GetPixelRed
### 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/file/d/1liJ7nJK0A4M_us-LuLZjwmqKXukx3nbO/view?usp=sharing)
please run a following cmd with poc file.
`magick $PoC -despeckle -flip -monochrome -alpha Shape tmp.rla`

Here's ASAN log.
```
==8370==ERROR: AddressSanitizer: heap-use-after-free on address 0x62a000024200 at pc 0x000000796779 bp 0x7ffdf7956b10 sp 0x7ffdf7956b08
READ of size 4 at 0x62a000024200 thread T0
    #0 0x796778 in GetPixelRed ImageMagick/./MagickCore/pixel-accessor.h:378:10
    #1 0x7938d7 in GetPixelIntensity ImageMagick/MagickCore/pixel.c:2367:24
    #2 0x258de7a in SetImageAlphaChannel ImageMagick/MagickCore/channel.c:1298:28
    #3 0x625776b in CLISimpleOperatorImage ImageMagick/MagickWand/operation.c:1765:18
    #4 0x6250c70 in CLISimpleOperatorImages ImageMagick/MagickWand/operation.c:3685:12
    #5 0x632eddb in CLIOption ImageMagick/MagickWand/operation.c:5302:16
    #6 0x5588f52 in ProcessCommandOptions ImageMagick/MagickWand/magick-cli.c:477:7
    #7 0x55910cc in MagickImageCommand ImageMagick/MagickWand/magick-cli.c:796:5
    #8 0x559b0e3 in MagickCommandGenesis ImageMagick/MagickWand/mogrify.c:185:14
    #9 0x51c3e5 in MagickMain ImageMagick/utilities/magick.c:149:10
    #10 0x519c69 in main ImageMagick/utilities/magick.c:180:10
    #11 0x7fdc4a357b96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310
    #12 0x421849 in _start (magick+0x421849)

0x62a000024200 is located 0 bytes inside of 22592-byte region [0x62a000024200,0x62a000029a40)
freed by thread T0 here:
    #0 0x4e1530 in __interceptor_free.localalias.0 (magick+0x4e1530)
    #1 0x6c76f0 in RelinquishAlignedMemory ImageMagick/MagickCore/memory.c:1037:3
    #2 0x245efb2 in RelinquishPixelCachePixels ImageMagick/MagickCore/cache.c:974:40
    #3 0x24e304f in OpenPixelCache ImageMagick/MagickCore/cache.c:3762:19
    #4 0x2506bd7 in GetImagePixelCache ImageMagick/MagickCore/cache.c:1757:18
    #5 0x2533d59 in SyncImagePixelCache ImageMagick/MagickCore/cache.c:5501:28
    #6 0x2601f04 in SetImageColorspace ImageMagick/MagickCore/colorspace.c:1244:10
    #7 0x2609fa7 in TransformsRGBImage ImageMagick/MagickCore/colorspace.c:1981:11
    #8 0x2605cc8 in TransformImageColorspace ImageMagick/MagickCore/colorspace.c:1407:12
    #9 0x70c801 in ConformPixelInfo ImageMagick/MagickCore/pixel.c:232:12
    #10 0x258da15 in SetImageAlphaChannel ImageMagick/MagickCore/channel.c:1294:9
    #11 0x625776b in CLISimpleOperatorImage ImageMagick/MagickWand/operation.c:1765:18
    #12 0x6250c70 in CLISimpleOperatorImages ImageMagick/MagickWand/operation.c:3685:12
    #13 0x632eddb in CLIOption ImageMagick/MagickWand/operation.c:5302:16
    #14 0x5588f52 in ProcessCommandOptions ImageMagick/MagickWand/magick-cli.c:477:7
    #15 0x55910cc in MagickImageCommand ImageMagick/MagickWand/magick-cli.c:796:5
    #16 0x559b0e3 in MagickCommandGenesis ImageMagick/MagickWand/mogrify.c:185:14
    #17 0x51c3e5 in MagickMain ImageMagick/utilities/magick.c:149:10
    #18 0x519c69 in main ImageMagick/utilities/magick.c:180:10
    #19 0x7fdc4a357b96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310

previously allocated by thread T0 here:
    #0 0x4e2338 in __interceptor_posix_memalign (magick+0x4e2338)
    #1 0x6bcd6a in AcquireAlignedMemory ImageMagick/MagickCore/memory.c:265:7
    #2 0x24e0cbd in OpenPixelCache ImageMagick/MagickCore/cache.c:3733:46
    #3 0x2506bd7 in GetImagePixelCache ImageMagick/MagickCore/cache.c:1757:18
    #4 0x2533d59 in SyncImagePixelCache ImageMagick/MagickCore/cache.c:5501:28
    #5 0x56d7ad in SetImageStorageClass ImageMagick/MagickCore/image.c:2625:10
    #6 0x258d244 in SetImageAlphaChannel ImageMagick/MagickCore/channel.c:1266:14
    #7 0x625776b in CLISimpleOperatorImage ImageMagick/MagickWand/operation.c:1765:18
    #8 0x6250c70 in CLISimpleOperatorImages ImageMagick/MagickWand/operation.c:3685:12
    #9 0x632eddb in CLIOption ImageMagick/MagickWand/operation.c:5302:16
    #10 0x5588f52 in ProcessCommandOptions ImageMagick/MagickWand/magick-cli.c:477:7
    #11 0x55910cc in MagickImageCommand ImageMagick/MagickWand/magick-cli.c:796:5
    #12 0x559b0e3 in MagickCommandGenesis ImageMagick/MagickWand/mogrify.c:185:14
    #13 0x51c3e5 in MagickMain ImageMagick/utilities/magick.c:149:10
    #14 0x519c69 in main ImageMagick/utilities/magick.c:180:10
    #15 0x7fdc4a357b96 in __libc_start_main /build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310

SUMMARY: AddressSanitizer: heap-use-after-free ImageMagick/./MagickCore/pixel-accessor.h:378:10 in GetPixelRed
Shadow bytes around the buggy address:
  0x0c547fffc7f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c547fffc800: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c547fffc810: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c547fffc820: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c547fffc830: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c547fffc840:[fd]fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc850: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc860: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc870: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc880: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c547fffc890: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
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
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  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
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==8370==ABORTING

```
### System Configuration
<!-- Tell us about the environment where you are experiencing the bug -->

- ImageMagick version:
Version: ImageMagick 7.0.8-68 Q16 x86_64 2019-10-06 https://imagemagick.org
- Environment (Operating system, version and so on):
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic

- Additional information:
CC=clang-6 CXX=clang++6 CFLAGS="-fsanitize=address,undefined -g" CXXFLAGS="-fsanitize=address,undefined -g" ./configure --disable-openmp


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

--- end body ---
