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[xen stable-4.12] tools/ocaml/xenstored: only Dom0 can change node owner

commit 3c13a871cb2188958fc41f43bc5c4d28c280cfd2
Author:     Edwin Török <edvin.torok@xxxxxxxxxx>
AuthorDate: Tue Dec 15 14:30:21 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Dec 15 14:30:21 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 
    demonstrating the vulnerability:
    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 52b88b3ee1..ef32f66991 100644
--- a/tools/ocaml/xenstored/store.ml
+++ b/tools/ocaml/xenstored/store.ml
@@ -430,7 +430,8 @@ 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-4.12



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