symlinked directories don't work as bind mount source on 1803 technical preview

[sesmith177]

Tested on Kernel Version: 10.0 17093 (17093.1000.amd64fre.rs_prerelease.180202-1400)

If the source of a bind mount is a symlink, container creation will succeed, but the directory will not be accessible inside the container. This is a regression from 1709. To reproduce:

$dockerImage = "microsoft/windowsservercore-insider:10.0.17093.1000"

$mountDir = "$env:TEMP\mountdir"
mkdir $mountDir

echo hello > "$mountDir\hello.txt"

$symlink = "$env:TEMP\symlink"
cmd.exe /c "mklink /D $symlink $mountDir"

docker run -v"$symlink":c:\containerDir $dockerImage cmd.exe /C "type c:\containerDir\hello.txt"

cmd.exe /c "rmdir $symlink"
rm -r -force $mountDir

The output of this script:

    Directory: C:\Windows\TEMP                                                                                                                 
                                                                                                                                               
                                                                                                                                               
Mode                LastWriteTime         Length Name                                                                                          
----                -------------         ------ ----                                                                                          
d-----         3/9/2018   9:09 AM                mountdir                                                                                      
symbolic link created for C:\Windows\TEMP\symlink <<===>> C:\Windows\TEMP\mountdir                                                             
The create operation failed because the name contained at least one mount point which resolves to a volume to which the specified device object is not attached.

On 1709, (with the container image changed appropriately) running the script show that the container mounts the symlinked directory correctly:

    Directory: C:\Windows\TEMP                                                    
                                                                                  
                                                                                  
Mode                LastWriteTime         Length Name                             
----                -------------         ------ ----                             
d-----         3/9/2018   9:07 AM                mountdir                         
symbolic link created for C:\Windows\TEMP\symlink <<===>> C:\Windows\TEMP\mountdir
hello                                                                             

[darstahl]

Thanks for the report. We caught this bug internally a few weeks ago and this bug is fixed in the latest internal builds 😄

Testing on Kernel Version: 10.0 17119 .... It will flight to insider builds soon.

PS C:\test> .\mount.ps1


    Directory: C:\Users\vmadmin\AppData\Local\Temp


Mode                LastWriteTime         Length Name
----                -------------         ------ ----
d-----         3/9/2018  12:52 PM                mountdir
symbolic link created for C:\Users\vmadmin\AppData\Local\Temp\symlink <<===>> C:\Users\vmadmin\AppData\Local\Temp\mountdir
hello