tools/xenstore: fix quota check in transaction_fix_domains()

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@xen.org>
Fixes: f2bebf72c4d5 ("xenstore: rework of transaction handling")
Signed-off-by: Juergen Gross <jgross@suse.com>
master commit: f6b801c36bd5e4ab22a9f80c8d57121b62b139af
master date: 2023-03-29 22:02:36 +0100

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index ccb7f0a92578d525870c84751aa2f72fb47fe9c7..feb7bbaa528c66e71bf788964d1f705d6747db4d 100644 (file)
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -1478,6 +1478,9 @@ 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_transaction.c b/tools/xenstore/xenstored_transaction.c
index ac854197cadbd95083a1f46bee7e48b9ebdfc5a1..8ebd16aed2d592e507627b85ea135960eb402216 100644 (file)
--- a/tools/xenstore/xenstored_transaction.c
+++ b/tools/xenstore/xenstored_transaction.c
@@ -172,12 +172,20 @@ 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)
 {
@@ -514,7 +522,12 @@ int do_transaction_start(const void *ctx, struct connection *conn,
        return 0;
 }
 
-static int transaction_fix_domains(struct transaction *trans, bool update)
+/*
+ * Update or check number of nodes per domain at the end of a transaction.
+ * If "update" is true, "chk_quota" is ignored.
+ */
+static int transaction_fix_domains(struct transaction *trans, bool chk_quota,
+                                  bool update)
 {
        struct changed_domain *d;
        int cnt;
@@ -522,7 +535,7 @@ static int transaction_fix_domains(struct transaction *trans, bool update)
        list_for_each_entry(d, &trans->changed_domains, list) {
                cnt = domain_entry_fix(d->domid, d->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;
@@ -538,6 +551,7 @@ 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")))
@@ -552,13 +566,15 @@ 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 = transaction_fix_domains(trans, false);
+               ret = transaction_fix_domains(trans, chk_quota, false);
                if (ret)
                        return ret;
                ret = finalize_transaction(conn, trans, &is_corrupt);
@@ -568,7 +584,7 @@ int do_transaction_end(const void *ctx, struct connection *conn,
                wrl_apply_debit_trans_commit(conn);
 
                /* fix domain entry for each changed domain */
-               transaction_fix_domains(trans, true);
+               transaction_fix_domains(trans, false, true);
 
                if (is_corrupt)
                        corrupt(conn, "transaction inconsistency");

diff --git a/tools/xenstore/xenstored_transaction.h b/tools/xenstore/xenstored_transaction.h
index 3417303f94272838086f8cfbf10f46eeea7dfc0c..f57d204cc06d7fc7c7d505068dcc53d5402a4bd5 100644 (file)
--- 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);
+
 /* inc/dec entry number local to trans while changing a node */
 void transaction_entry_inc(struct transaction *trans, unsigned int domid);
 void transaction_entry_dec(struct transaction *trans, unsigned int domid);