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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging-4.16] tools/xenstore: limit max number of nodes accessed in a transaction
commit 7017cfefc455db535054ebc09124af8101746a4a
Author: Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Tue Sep 13 07:35:09 2022 +0200
Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Nov 1 14:07:24 2022 +0000
tools/xenstore: limit max number of nodes accessed in a transaction
Today a guest is free to access as many nodes in a single transaction
as it wants. This can lead to unbounded memory consumption in Xenstore
as there is the need to keep track of all nodes having been accessed
during a transaction.
In oxenstored the number of requests in a transaction is being limited
via a quota maxrequests (default is 1024). As multiple accesses of a
node are not problematic in C Xenstore, limit the number of accessed
nodes.
In order to let read_node() detect a quota error in case too many nodes
are being accessed, check the return value of access_node() and return
NULL in case an error has been seen. Introduce __must_check and add it
to the access_node() prototype.
This is part of XSA-326 / CVE-2022-42314.
Suggested-by: Julien Grall <julien@xxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
(cherry picked from commit 268369d8e322d227a74a899009c5748d7b0ea142)
---
tools/include/xen-tools/libs.h | 4 +++
tools/xenstore/xenstored_core.c | 50 ++++++++++++++++++++++++----------
tools/xenstore/xenstored_core.h | 1 +
tools/xenstore/xenstored_transaction.c | 9 ++++++
tools/xenstore/xenstored_transaction.h | 4 +--
5 files changed, 52 insertions(+), 16 deletions(-)
diff --git a/tools/include/xen-tools/libs.h b/tools/include/xen-tools/libs.h
index a16e0c3807..bafc90e2f6 100644
--- a/tools/include/xen-tools/libs.h
+++ b/tools/include/xen-tools/libs.h
@@ -63,4 +63,8 @@
#define ROUNDUP(_x,_w) (((unsigned long)(_x)+(1UL<<(_w))-1) & ~((1UL<<(_w))-1))
#endif
+#ifndef __must_check
+#define __must_check __attribute__((__warn_unused_result__))
+#endif
+
#endif /* __XEN_TOOLS_LIBS__ */
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 692d863fce..f835aa1b2f 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -106,6 +106,7 @@ int quota_nb_watch_per_domain = 128;
int quota_max_entry_size = 2048; /* 2K */
int quota_max_transaction = 10;
int quota_nb_perms_per_node = 5;
+int quota_trans_nodes = 1024;
int quota_max_path_len = XENSTORE_REL_PATH_MAX;
int quota_req_outstanding = 20;
@@ -595,6 +596,7 @@ struct node *read_node(struct connection *conn, const void
*ctx,
TDB_DATA key, data;
struct xs_tdb_record_hdr *hdr;
struct node *node;
+ int err;
node = talloc(ctx, struct node);
if (!node) {
@@ -616,14 +618,13 @@ struct node *read_node(struct connection *conn, const
void *ctx,
if (data.dptr == NULL) {
if (tdb_error(tdb_ctx) == TDB_ERR_NOEXIST) {
node->generation = NO_GENERATION;
- access_node(conn, node, NODE_ACCESS_READ, NULL);
- errno = ENOENT;
+ err = access_node(conn, node, NODE_ACCESS_READ, NULL);
+ errno = err ? : ENOENT;
} else {
log("TDB error on read: %s", tdb_errorstr(tdb_ctx));
errno = EIO;
}
- talloc_free(node);
- return NULL;
+ goto error;
}
node->parent = NULL;
@@ -638,19 +639,36 @@ struct node *read_node(struct connection *conn, const
void *ctx,
/* Permissions are struct xs_permissions. */
node->perms.p = hdr->perms;
- if (domain_adjust_node_perms(conn, node)) {
- talloc_free(node);
- return NULL;
- }
+ if (domain_adjust_node_perms(conn, node))
+ goto error;
/* Data is binary blob (usually ascii, no nul). */
node->data = node->perms.p + hdr->num_perms;
/* Children is strings, nul separated. */
node->children = node->data + node->datalen;
- access_node(conn, node, NODE_ACCESS_READ, NULL);
+ if (access_node(conn, node, NODE_ACCESS_READ, NULL))
+ goto error;
return node;
+
+ error:
+ err = errno;
+ talloc_free(node);
+ errno = err;
+ return NULL;
+}
+
+static bool read_node_can_propagate_errno(void)
+{
+ /*
+ * 2 error cases for read_node() can always be propagated up:
+ * ENOMEM, because this has nothing to do with the node being in the
+ * data base or not, but is caused by a general lack of memory.
+ * ENOSPC, because this is related to hitting quota limits which need
+ * to be respected.
+ */
+ return errno == ENOMEM || errno == ENOSPC;
}
int write_node_raw(struct connection *conn, TDB_DATA *key, struct node *node,
@@ -767,7 +785,7 @@ static int ask_parents(struct connection *conn, const void
*ctx,
node = read_node(conn, ctx, name);
if (node)
break;
- if (errno == ENOMEM)
+ if (read_node_can_propagate_errno())
return errno;
} while (!streq(name, "/"));
@@ -829,7 +847,7 @@ static struct node *get_node(struct connection *conn,
}
}
/* Clean up errno if they weren't supposed to know. */
- if (!node && errno != ENOMEM)
+ if (!node && !read_node_can_propagate_errno())
errno = errno_from_parents(conn, ctx, name, errno, perm);
return node;
}
@@ -1235,7 +1253,7 @@ static struct node *construct_node(struct connection
*conn, const void *ctx,
/* If parent doesn't exist, create it. */
parent = read_node(conn, parentname, parentname);
- if (!parent)
+ if (!parent && errno == ENOENT)
parent = construct_node(conn, ctx, parentname);
if (!parent)
return NULL;
@@ -1509,7 +1527,7 @@ static int _rm(struct connection *conn, const void *ctx,
struct node *node,
parent = read_node(conn, ctx, parentname);
if (!parent)
- return (errno == ENOMEM) ? ENOMEM : EINVAL;
+ return read_node_can_propagate_errno() ? errno : EINVAL;
node->parent = parent;
return delete_node(conn, ctx, parent, node, false);
@@ -1539,7 +1557,7 @@ static int do_rm(struct connection *conn, struct
buffered_data *in)
return 0;
}
/* Restore errno, just in case. */
- if (errno != ENOMEM)
+ if (!read_node_can_propagate_errno())
errno = ENOENT;
}
return errno;
@@ -2384,6 +2402,8 @@ static void usage(void)
" -M, --path-max <chars> limit the allowed Xenstore node path length,\n"
" -Q, --quota <what>=<nb> set the quota <what> to the value <nb>, allowed\n"
" quotas are:\n"
+" transaction-nodes: number of accessed node per\n"
+" transaction\n"
" outstanding: number of outstanding requests\n"
" -w, --timeout <what>=<seconds> set the timeout in seconds for <what>,\n"
" allowed timeout candidates are:\n"
@@ -2468,6 +2488,8 @@ static void set_quota(const char *arg)
val = get_optval_int(eq + 1);
if (what_matches(arg, "outstanding"))
quota_req_outstanding = val;
+ else if (what_matches(arg, "transaction-nodes"))
+ quota_trans_nodes = val;
else
barf("unknown quota \"%s\"\n", arg);
}
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index b1a70488b9..245f925823 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -268,6 +268,7 @@ extern int dom0_event;
extern int priv_domid;
extern int quota_nb_entry_per_domain;
extern int quota_req_outstanding;
+extern int quota_trans_nodes;
extern unsigned int timeout_watch_event_msec;
diff --git a/tools/xenstore/xenstored_transaction.c
b/tools/xenstore/xenstored_transaction.c
index 86caf6c398..7bd41eb475 100644
--- a/tools/xenstore/xenstored_transaction.c
+++ b/tools/xenstore/xenstored_transaction.c
@@ -156,6 +156,9 @@ struct transaction
/* Connection-local identifier for this transaction. */
uint32_t id;
+ /* Node counter. */
+ unsigned int nodes;
+
/* Generation when transaction started. */
uint64_t generation;
@@ -260,6 +263,11 @@ int access_node(struct connection *conn, struct node *node,
i = find_accessed_node(trans, node->name);
if (!i) {
+ if (trans->nodes >= quota_trans_nodes &&
+ domain_is_unprivileged(conn)) {
+ ret = ENOSPC;
+ goto err;
+ }
i = talloc_zero(trans, struct accessed_node);
if (!i)
goto nomem;
@@ -297,6 +305,7 @@ int access_node(struct connection *conn, struct node *node,
i->ta_node = true;
}
}
+ trans->nodes++;
list_add_tail(&i->list, &trans->accessed);
}
diff --git a/tools/xenstore/xenstored_transaction.h
b/tools/xenstore/xenstored_transaction.h
index 0093cac807..e3cbd6b230 100644
--- a/tools/xenstore/xenstored_transaction.h
+++ b/tools/xenstore/xenstored_transaction.h
@@ -39,8 +39,8 @@ void transaction_entry_inc(struct transaction *trans,
unsigned int domid);
void transaction_entry_dec(struct transaction *trans, unsigned int domid);
/* This node was accessed. */
-int access_node(struct connection *conn, struct node *node,
- enum node_access_type type, TDB_DATA *key);
+int __must_check access_node(struct connection *conn, struct node *node,
+ enum node_access_type type, TDB_DATA *key);
/* Queue watches for a modified node. */
void queue_watches(struct connection *conn, const char *name, bool
watch_exact);
--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.16
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