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

[Konstantin Khlebnikov]

On Tue, Mar 10, 2015 at 8:32 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> 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.

Setting project id mapping for nested user-namespace also requires
this capability in parent namespace. The same as for setting uid/gid
mapping but without special case for mapping current uid/gid because
task has no "current" project id.

This is mentioned in cover letter but I forget it here. Sorry.

>
> --Andy
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