fuse doesn't use security_inode_init_security?

[Miklos Szeredi]

On Fri, May 1, 2020 at 8:55 AM Chirantan Ekbote <chirantan at chromium.org> wrote:
>
> Hello,
>
> I noticed that the fuse module doesn't currently call
> security_inode_init_security and I was wondering if there is a
> specific reason for that.  I found a patch from 2013[1] that would
> change fuse so that it would call that function but it doesn't appear
> that the patch was merged.
>
> For background: I currently have a virtio-fs server with a guest VM
> that wants to use selinux.  I was able to enable selinux support
> without much issue by adding
>
>     fs_use_xattr virtiofs u:object_r:labeledfs:s0;
>
> to the selinux policy in the guest.  This works for the most part
> except that `setfscreatecon` doesn't appear to work.  From what I can
> tell, this ends up writing to `/proc/[pid]/attr/fscreate` and the
> attributes actually get set via the `inode_init_security` lsm hook in
> selinux.  However, since fuse doesn't call
> `security_inode_init_security` the hook never runs so the
> file/directory doesn't have the right attributes.
>
> Is it safe to just call `security_inode_init_security` whenever fuse
> creates a new inode?  How does this affect non-virtiofs fuse servers?

Not sure,  Adding more Cc's.

I know there's a deadlock scenario with getxattr called on root inode
before mount returns, which causes a deadlock unless mount is run in
the background.  Current libfuse doesn't handle this, but I think some
fuse fs work around this by not using libfuse, or at least have some
special setup code (glusterfs? ceph-fuse? not sure...).  I also don't
know whether the ->inode_init_security hook is related to this or not.


Thanks,
Miklos