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xen.27494
xsa326-09.patch
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File xsa326-09.patch of Package xen.27494
From 7d313f4322e44425882b21764bc9c42a790d030a Mon Sep 17 00:00:00 2001 From: Juergen Gross <jgross@suse.com> Date: Tue, 13 Sep 2022 07:35:09 +0200 Subject: 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@xen.org> Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Julien Grall <jgrall@amazon.com> diff --git a/tools/include/xen-tools/libs.h b/tools/include/xen-tools/libs.h index cc7dfc8c6453..34db3b784732 100644 --- a/tools/include/xen-tools/libs.h +++ b/tools/include/xen-tools/libs.h @@ -59,4 +59,8 @@ }) #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 98d242e06241..57c999129215 100644 --- a/tools/xenstore/xenstored_core.c +++ b/tools/xenstore/xenstored_core.c @@ -102,6 +102,7 @@ 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_req_outstanding = 20; unsigned int timeout_watch_event_msec = 20000; @@ -500,6 +501,7 @@ 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) { @@ -521,14 +523,13 @@ 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; @@ -543,19 +544,36 @@ 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, @@ -670,7 +688,7 @@ 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, "/")); @@ -733,7 +751,7 @@ 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; } @@ -1115,7 +1133,7 @@ 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; @@ -1394,7 +1412,7 @@ 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); @@ -1422,7 +1440,7 @@ 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; @@ -2192,6 +2210,8 @@ static void usage(void) " -A, --perm-nb <nb> limit the number of permissions per node,\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" @@ -2273,6 +2293,8 @@ 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 98db4afcaabf..7e371253d2d1 100644 --- a/tools/xenstore/xenstored_core.h +++ b/tools/xenstore/xenstored_core.h @@ -34,6 +34,7 @@ #include "list.h" #include "tdb.h" #include "hashtable.h" +#include "utils.h" /* DEFAULT_BUFFER_SIZE should be large enough for each errno string. */ #define DEFAULT_BUFFER_SIZE 16 @@ -223,6 +224,7 @@ 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 bf2fda8234b3..778b7e439cb3 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; @@ -266,6 +269,11 @@ 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; @@ -303,6 +311,7 @@ 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 0093cac807e3..e3cbd6b23095 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);
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