Messages in this thread | | | From | (Eric W. Biederman) | Date | Tue, 12 Jan 2021 12:49:12 -0600 | Subject | Re: [PATCH v2 01/10] vfs: move cap_convert_nscap() call into vfs_setxattr() |
| |
ebiederm@xmission.com (Eric W. Biederman) writes:
> So there is the basic question do we want to read the raw bytes on disk > or do we want to return something meaningful to the reader. As the > existing tools use the xattr interface to set/clear fscaps returning > data to user space rather than raw bytes seems the perfered interface. > > My ideal semantics would be: > > - If current_user_ns() == sb->s_user_ns return the raw data. > > I don't know how to implement this first scenario while permitting > stacked filesystems.
After a little more thought I do.
In getxattr if the get_cap method is not implemented by the filesystem if current_user_ns() == sb->s_user_ns simply treat it as an ordinary xattr read/write.
Otherwise call vfs_get_cap and translate the result as described below.
The key point of this is it allows for seeing what is actually on disk (when it is not confusing).
> - Calculate the cpu_vfs_cap_data as get_vfs_caps_from_disk does. > That gives the meaning of the xattr. > > - If "from_kuid(current_userns(), krootid) == 0" return a v2 cap. > > - If "rootid_owns_currentns()" return a v2 cap. > > - Else return an error. Probably a permission error. > > The fscap simply can not make sense to the user if the rootid does not > map. Return a v2 cap would imply that the caps are present on the > executable (in the current context) which they are not.
Eric
| |