samba - Jan 2021 - symlinks loop detection in Samba?

On Tue, Jan 19, 2021 at 04:05:47PM +0100, Giuseppe Lo Presti via samba
wrote:
>
>Thanks a lot Ralph,
>
>To be honest I did not wait for the 40 resolutions to be exceeded, as 
>currently [*] implemented by the kernel, and thought that some loop 
>detection would get triggered earlier (similarly to how e.g. `find -L` 
>is implemented). Indeed I confirm that a Windows client looking to the 
>properties of a shared folder with only one symlink to '.' does see 
>exactly 40 folders, so it's all consistent.
>
>At the same time, I acknowledge we must keep a loop protection in our 
>filesystem, because in the general case it does take too much time to 
>reach 40 path resolutions when a real folder structure is involved, 
>and a DoS is already happening.
>
>Cheers,
>Giuseppe
>
>
>P.S.: out of curiosity, why did you say "I hate to say, symlinks are 
>fully supported"? :-)
Symlinks are a blight on a perfectly well designed filesystem. Once
the VFS work is finished, expect an epic rant (talk :-) I'm planning
to give :-). Not often I'll say this, but Microsoft got it right
in Windows on this point.

On 19/01/2021 17:37, Jeremy Allison via samba wrote:
> On Tue, Jan 19, 2021 at 04:05:47PM +0100, Giuseppe Lo Presti via samba 
> wrote:
>>
>> Thanks a lot Ralph,
>>
>> To be honest I did not wait for the 40 resolutions to be exceeded, as 
>> currently [*] implemented by the kernel, and thought that some loop 
>> detection would get triggered earlier (similarly to how e.g. `find 
>> -L` is implemented). Indeed I confirm that a Windows client looking 
>> to the properties of a shared folder with only one symlink to
'.'
>> does see exactly 40 folders, so it's all consistent.
>>
>> At the same time, I acknowledge we must keep a loop protection in our 
>> filesystem, because in the general case it does take too much time to 
>> reach 40 path resolutions when a real folder structure is involved, 
>> and a DoS is already happening.
>>
>> Cheers,
>> Giuseppe
>>
>>
>> P.S.: out of curiosity, why did you say "I hate to say, symlinks
are
>> fully supported"? :-)
>
> Symlinks are a blight on a perfectly well designed filesystem. Once
> the VFS work is finished, expect an epic rant (talk :-) I'm planning
> to give :-). Not often I'll say this, but Microsoft got it right
> in Windows on this point.
>
Which is why I never understood why the default for 'follow symlinks' is
'yes'. I also cannot understand why 'allow insecure wide links'
was
created, probably someone asked for it, but they should have been told no.

Rowland