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Date: Tue, 3 Jul 2018 20:48:54 +0200
From: Jann Horn <jannh@...gle.com>
To: hanno@...eck.de
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: Patch for SymlinksIfOwnerMatches

On Tue, Jul 3, 2018 at 8:29 PM Hanno Böck <hanno@...eck.de> wrote:
> There's a nasty problem in many webserver configurations on multiuser
> systems, I've blogged about it a while ago [1]. With a symlink it's
> often possible to read out configuration files of other users. This was
> famously used in the freedom hosting II hack [2].
>
> grsecurity had a workaround for this: By not allowing file operations
> to follow symlinks if the owner of the link and the target don't match
> it can block this kind of attack.
>
> I saw a need to keep this feature alive in a post-grsecurity world, so
> a while ago I extracted it from the grsecurity patch. I've now made
> that public:
> https://github.com/hannob/symlinkown
>
> I'm not sure about upstreaming, I think it's a worthy feature, but it
> might need some work in polishing it. But for now I'll just share it
> and I will hopefully be able to keep the patch working for future
> kernels.
>
> [1]
> https://blog.hboeck.de/archives/873-The-tricky-security-issue-with-FollowSymLinks-and-Apache.html
> [2]
> https://securityaffairs.co/wordpress/55990/deep-web/freedom-hosting-ii-hack.html

Does upstream's /proc/sys/fs/protected_symlinks not work for that?

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