[xen stable-4.10] tools/ocaml/xenstored: only Dom0 can change node owner

[patchbot@xxxxxxx]

commit fef52f19ed59bbb379b04a711079c67aaaf788d4
Author:     Edwin Török <edvin.torok@xxxxxxxxxx>
AuthorDate: Tue Dec 15 14:45:47 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Dec 15 14:45:47 2020 +0100

    tools/ocaml/xenstored: only Dom0 can change node owner
    
    Otherwise we can give quota away to another domain, either causing it to run
    out of quota, or in case of Dom0 use unbounded amounts of memory and bypass
    the quota system entirely.
    
    This was fixed in the C version of xenstored in 2006 (c/s db34d2aaa5f5,
    predating the XSA process by 5 years).
    
    It was also fixed in the mirage version of xenstore in 2012, with a unit 
test
    demonstrating the vulnerability:
    
      
https://github.com/mirage/ocaml-xenstore/commit/6b91f3ac46b885d0530a51d57a9b3a57d64923a7
      
https://github.com/mirage/ocaml-xenstore/commit/22ee5417c90b8fda905c38de0d534506152eace6
    
    but possibly without realising that the vulnerability still affected the
    in-tree oxenstored (added c/s f44af660412 in 2010).
    
    This is XSA-352.
    
    Signed-off-by: Edwin Török <edvin.torok@xxxxxxxxxx>
    Acked-by: Christian Lindig <christian.lindig@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/ocaml/xenstored/store.ml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/ocaml/xenstored/store.ml b/tools/ocaml/xenstored/store.ml
index 6bbbd05552..2a694562bb 100644
--- a/tools/ocaml/xenstored/store.ml
+++ b/tools/ocaml/xenstored/store.ml
@@ -437,7 +437,8 @@ let setperms store perm path nperms =
        | Some node ->
                let old_owner = Node.get_owner node in
                let new_owner = Perms.Node.get_owner nperms in
-               if not ((old_owner = new_owner) || (Perms.Connection.is_dom0 
perm)) then Quota.check store.quota new_owner 0;
+               if not ((old_owner = new_owner) || (Perms.Connection.is_dom0 
perm)) then
+                       raise Define.Permission_denied;
                store.root <- path_setperms store perm path nperms;
                Quota.del_entry store.quota old_owner;
                Quota.add_entry store.quota new_owner
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.10