On Thu, Sep 29, 2022 at 02:18:43PM +0200, Mickaël Salaün wrote: > > On 29/09/2022 13:37, Christian Brauner wrote: > > On Thu, Sep 29, 2022 at 12:04:47PM +0200, Mickaël Salaün wrote: > > > A kernel daemon should not rely on the current thread, which is unknown > > > and might be malicious. Before this security fix, > > > ksmbd_override_fsids() didn't correctly override FS UID/GID which means > > > that arbitrary user space threads could trick the kernel to impersonate > > > arbitrary users or groups for file system access checks, leading to > > > file system access bypass. > > > > > > This was found while investigating truncate support for Landlock: > > > https://lore.kernel.org/r/CAKYAXd8fpMJ7guizOjHgxEyyjoUwPsx3jLOPZP=wPYcbhkVXqA@xxxxxxxxxxxxxx > > > > > > Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") > > > Cc: Hyunchul Lee <hyc.lee@xxxxxxxxx> > > > Cc: Namjae Jeon <linkinjeon@xxxxxxxxxx> > > > Cc: Steve French <smfrench@xxxxxxxxx> > > > Cc: stable@xxxxxxxxxxxxxxx > > > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx> > > > Link: https://lore.kernel.org/r/20220929100447.108468-1-mic@xxxxxxxxxxx > > > --- > > > > I think this is ok. The alternative would probably be to somehow use a > > relevant userns when struct ksmbd_user is created when the session is > > established. But these are deeper ksmbd design questions. The fix > > proposed here itself seems good. > > That would be better indeed. I guess ksmbd works whenever the netlink peer > is not in a user namespace with mapped UID/GID, but it should result in > obvious access bugs otherwise (which is already the case anyway). It seems > that the netlink peer must be trusted because it is the source of truth for > account/user mapping anyway. This change fixes the more critical side of the > issue and it should fit well for backports. Sorry, I also forgot, Acked-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
