[PATCH v2] tools/xenstore: fix quota check in acc_fix_domains()

[Juergen Gross <jgross@xxxxxxxx>]

Today when finalizing a transaction the number of node quota is checked
to not being exceeded after the transaction. This check is always done,
even if the transaction is being performed by a privileged connection,
or if there were no nodes created in the transaction.

Correct that by checking quota only if:
- the transaction is being performed by an unprivileged guest, and
- at least one node was created in the transaction

Reported-by: Julien Grall <julien@xxxxxxx>
Fixes: f2bebf72c4d5 ("xenstore: rework of transaction handling")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V2:
- add comment (Julien Grall)
---
 tools/xenstore/xenstored_core.c        |  3 +++
 tools/xenstore/xenstored_domain.c      |  4 ++--
 tools/xenstore/xenstored_domain.h      |  7 ++++++-
 tools/xenstore/xenstored_transaction.c | 16 ++++++++++++++--
 tools/xenstore/xenstored_transaction.h |  3 +++
 5 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index a61db2db2d..3ca68681e3 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -1472,6 +1472,9 @@ static struct node *create_node(struct connection *conn, 
const void *ctx,
        if (!node)
                return NULL;
 
+       if (conn && conn->transaction)
+               ta_node_created(conn->transaction);
+
        node->data = data;
        node->datalen = datalen;
 
diff --git a/tools/xenstore/xenstored_domain.c 
b/tools/xenstore/xenstored_domain.c
index d7fc2fafc7..f62be2245c 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -544,7 +544,7 @@ static struct domain *find_domain_by_domid(unsigned int 
domid)
        return (d && d->introduced) ? d : NULL;
 }
 
-int acc_fix_domains(struct list_head *head, bool update)
+int acc_fix_domains(struct list_head *head, bool chk_quota, bool update)
 {
        struct changed_domain *cd;
        int cnt;
@@ -552,7 +552,7 @@ int acc_fix_domains(struct list_head *head, bool update)
        list_for_each_entry(cd, head, list) {
                cnt = domain_nbentry_fix(cd->domid, cd->nbentry, update);
                if (!update) {
-                       if (cnt >= quota_nb_entry_per_domain)
+                       if (chk_quota && cnt >= quota_nb_entry_per_domain)
                                return ENOSPC;
                        if (cnt < 0)
                                return ENOMEM;
diff --git a/tools/xenstore/xenstored_domain.h 
b/tools/xenstore/xenstored_domain.h
index dc4660861e..279cccb3ad 100644
--- a/tools/xenstore/xenstored_domain.h
+++ b/tools/xenstore/xenstored_domain.h
@@ -96,7 +96,12 @@ void domain_outstanding_dec(struct connection *conn);
 void domain_outstanding_domid_dec(unsigned int domid);
 int domain_get_quota(const void *ctx, struct connection *conn,
                     unsigned int domid);
-int acc_fix_domains(struct list_head *head, bool update);
+
+/*
+ * Update or check number of nodes per domain at the end of a transaction.
+ * If "update" is true, "chk_quota" is ignored.
+ */
+int acc_fix_domains(struct list_head *head, bool chk_quota, bool update);
 
 /* Write rate limiting */
 
diff --git a/tools/xenstore/xenstored_transaction.c 
b/tools/xenstore/xenstored_transaction.c
index 1aa9d3cb3d..2b15506953 100644
--- a/tools/xenstore/xenstored_transaction.c
+++ b/tools/xenstore/xenstored_transaction.c
@@ -160,12 +160,20 @@ struct transaction
        /* List of changed domains - to record the changed domain entry number 
*/
        struct list_head changed_domains;
 
+       /* There was at least one node created in the transaction. */
+       bool node_created;
+
        /* Flag for letting transaction fail. */
        bool fail;
 };
 
 uint64_t generation;
 
+void ta_node_created(struct transaction *trans)
+{
+       trans->node_created = true;
+}
+
 static struct accessed_node *find_accessed_node(struct transaction *trans,
                                                const char *name)
 {
@@ -509,6 +517,7 @@ int do_transaction_end(const void *ctx, struct connection 
*conn,
        const char *arg = onearg(in);
        struct transaction *trans;
        bool is_corrupt = false;
+       bool chk_quota;
        int ret;
 
        if (!arg || (!streq(arg, "T") && !streq(arg, "F")))
@@ -523,13 +532,16 @@ int do_transaction_end(const void *ctx, struct connection 
*conn,
        if (!conn->transaction_started)
                conn->ta_start_time = 0;
 
+       chk_quota = trans->node_created && domain_is_unprivileged(conn);
+
        /* Attach transaction to ctx for auto-cleanup */
        talloc_steal(ctx, trans);
 
        if (streq(arg, "T")) {
                if (trans->fail)
                        return ENOMEM;
-               ret = acc_fix_domains(&trans->changed_domains, false);
+               ret = acc_fix_domains(&trans->changed_domains, chk_quota,
+                                     false);
                if (ret)
                        return ret;
                ret = finalize_transaction(conn, trans, &is_corrupt);
@@ -539,7 +551,7 @@ int do_transaction_end(const void *ctx, struct connection 
*conn,
                wrl_apply_debit_trans_commit(conn);
 
                /* fix domain entry for each changed domain */
-               acc_fix_domains(&trans->changed_domains, true);
+               acc_fix_domains(&trans->changed_domains, false, true);
 
                if (is_corrupt)
                        corrupt(conn, "transaction inconsistency");
diff --git a/tools/xenstore/xenstored_transaction.h 
b/tools/xenstore/xenstored_transaction.h
index b6f8cb7d0a..883145163f 100644
--- a/tools/xenstore/xenstored_transaction.h
+++ b/tools/xenstore/xenstored_transaction.h
@@ -36,6 +36,9 @@ int do_transaction_end(const void *ctx, struct connection 
*conn,
 
 struct transaction *transaction_lookup(struct connection *conn, uint32_t id);
 
+/* Set flag for created node. */
+void ta_node_created(struct transaction *trans);
+
 /* This node was accessed. */
 int __must_check access_node(struct connection *conn, struct node *node,
                              enum node_access_type type, TDB_DATA *key);
-- 
2.35.3