Re: [PATCH RFC v2 2/6] fs: protected project id

From: Andy Lutomirski
Date: Tue Mar 10 2015 - 13:33:19 EST

On Tue, Mar 10, 2015 at 10:22 AM, Konstantin Khlebnikov
<khlebnikov@xxxxxxxxxxxxxx> wrote:
> Historically XFS project id doesn't have any permission control: file owner
> is able to set any project id. Later they was sealed with user-namespace:
> XFS allows to change it only from init user-ns. That works fine for isolated
> containers or if user doesn't have direct access to the filesystem (NFS/FTP).
> This patch adds sysctl fs.protected_projects which makes changing project id
> privileged operation which requires CAP_SYS_RESOURCE in current user-namespace.
> Thus there are two levels of protection: project id mapping in user-ns defines
> set of permitted projects and capability protects operations within this set.

If I understand this right, this doesn't work. If I lack
CAP_SYS_RESOURCE but I have two projids mapped, then I can create a
new userns, map both projids, and get CAP_SYS_RESOURCE.

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