[xen staging] tools/ocaml/xenstored: Check for maxrequests before performing operations

[patchbot@xxxxxxx]

commit 329f4d1a6535c6c5a34025ca0d03fc5c7228fcff
Author:     Edwin Török <edvin.torok@xxxxxxxxxx>
AuthorDate: Thu Jul 28 17:08:15 2022 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Nov 1 13:05:44 2022 +0000

    tools/ocaml/xenstored: Check for maxrequests before performing operations
    
    Previously we'd perform the operation, record the updated tree in the
    transaction record, then try to insert a watchop path and the reply packet.
    
    If we exceeded max requests we would've returned EQUOTA, but still:
    * have performed the operation on the transaction's tree
    * have recorded the watchop, making this queue effectively unbounded
    
    It is better if we check whether we'd have room to store the operation 
before
    performing the transaction, and raise EQUOTA there.  Then the transaction
    record won't grow.
    
    This is part of XSA-326 / CVE-2022-42317.
    
    Signed-off-by: Edwin Török <edvin.torok@xxxxxxxxxx>
    Acked-by: Christian Lindig <christian.lindig@xxxxxxxxxx>
---
 tools/ocaml/xenstored/process.ml     |  4 +++-
 tools/ocaml/xenstored/transaction.ml | 16 ++++++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml
index 86eed02413..d0400419ab 100644
--- a/tools/ocaml/xenstored/process.ml
+++ b/tools/ocaml/xenstored/process.ml
@@ -389,6 +389,7 @@ let input_handle_error ~cons ~doms ~fct ~con ~t ~req =
        let reply_error e =
                Packet.Error e in
        try
+               Transaction.check_quota_exn ~perm:(Connection.get_perm con) t;
                fct con t doms cons req.Packet.data
        with
        | Define.Invalid_path          -> reply_error "EINVAL"
@@ -682,9 +683,10 @@ let process_packet ~store ~cons ~doms ~con ~req =
                in
 
                let response = try
+                       Transaction.check_quota_exn ~perm:(Connection.get_perm 
con) t;
                        if tid <> Transaction.none then
                                (* Remember the request and response for this 
operation in case we need to replay the transaction *)
-                               Transaction.add_operation 
~perm:(Connection.get_perm con) t req response;
+                               Transaction.add_operation t req response;
                        response
                with Quota.Limit_reached ->
                        Packet.Error "EQUOTA"
diff --git a/tools/ocaml/xenstored/transaction.ml 
b/tools/ocaml/xenstored/transaction.ml
index 17b1bdf2ea..294143e233 100644
--- a/tools/ocaml/xenstored/transaction.ml
+++ b/tools/ocaml/xenstored/transaction.ml
@@ -85,6 +85,7 @@ type t = {
        oldroot: Store.Node.t;
        mutable paths: (Xenbus.Xb.Op.operation * Store.Path.t) list;
        mutable operations: (Packet.request * Packet.response) list;
+       mutable quota_reached: bool;
        mutable read_lowpath: Store.Path.t option;
        mutable write_lowpath: Store.Path.t option;
 }
@@ -127,6 +128,7 @@ let make ?(internal=false) id store =
                oldroot = Store.get_root store;
                paths = [];
                operations = [];
+               quota_reached = false;
                read_lowpath = None;
                write_lowpath = None;
        } in
@@ -143,13 +145,19 @@ let get_root t = Store.get_root t.store
 
 let is_read_only t = t.paths = []
 let add_wop t ty path = t.paths <- (ty, path) :: t.paths
-let add_operation ~perm t request response =
+let get_operations t = List.rev t.operations
+
+let check_quota_exn ~perm t =
        if !Define.maxrequests >= 0
                && not (Perms.Connection.is_dom0 perm)
-               && List.length t.operations >= !Define.maxrequests
-               then raise Quota.Limit_reached;
+               && (t.quota_reached || List.length t.operations >= 
!Define.maxrequests)
+               then begin
+                       t.quota_reached <- true;
+                       raise Quota.Limit_reached;
+               end
+
+let add_operation t request response =
        t.operations <- (request, response) :: t.operations
-let get_operations t = List.rev t.operations
 let set_read_lowpath t path = t.read_lowpath <- get_lowest path t.read_lowpath
 let set_write_lowpath t path = t.write_lowpath <- get_lowest path 
t.write_lowpath
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging