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xen.28173
xsa326-05.patch
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File xsa326-05.patch of Package xen.28173
From c3e397f2d77645584cc955c223b2894a4239ea4c Mon Sep 17 00:00:00 2001 From: Juergen Gross <jgross@suse.com> Date: Tue, 13 Sep 2022 07:35:08 +0200 Subject: tools/xenstore: limit outstanding requests Add another quota for limiting the number of outstanding requests of a guest. As the way to specify quotas on the command line is becoming rather nasty, switch to a new scheme using [--quota|-Q] <what>=<val> allowing to add more quotas in future easily. Set the default value to 20 (basically a random value not seeming to be too high or too low). A request is said to be outstanding if any message generated by this request (the direct response plus potential watch events) is not yet completely stored into a ring buffer. The initial watch event sent as a result of registering a watch is an exception. Note that across a live update the relation to buffered watch events for other domains is lost. Use talloc_zero() for allocating the domain structure in order to have all per-domain quota zeroed initially. This is part of XSA-326 / CVE-2022-42312. Signed-off-by: Juergen Gross <jgross@suse.com> Acked-by: Julien Grall <jgrall@amazon.com> --- 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_req_outstanding = 20; unsigned int timeout_watch_event_msec = 20000; @@ -217,12 +218,24 @@ static uint64_t get_now_msec(void) return now_ts.tv_sec * 1000 + now_ts.tv_nsec / 1000000; } +/* + * Remove a struct buffered_data from the list of outgoing data. + * A struct buffered_data related to a request having caused watch events to be + * sent is kept until all those events have been written out. + * Each watch event is referencing the related request via pend.req, while the + * number of watch events caused by a request is kept in pend.ref.event_cnt + * (those two cases are mutually exclusive, so the two fields can share memory + * via a union). + * The struct buffered_data is freed only if no related watch event is + * referencing it. The related return data can be freed right away. + */ static void free_buffered_data(struct buffered_data *out, struct connection *conn) { struct buffered_data *req; list_del(&out->list); + out->on_out_list = false; /* * Update conn->timeout_msec with the next found timeout value in the @@ -238,6 +251,30 @@ static void free_buffered_data(struct bu } } + if (out->hdr.msg.type == XS_WATCH_EVENT) { + req = out->pend.req; + if (req) { + req->pend.ref.event_cnt--; + if (!req->pend.ref.event_cnt && !req->on_out_list) { + if (req->on_ref_list) { + domain_outstanding_domid_dec( + req->pend.ref.domid); + list_del(&req->list); + } + talloc_free(req); + } + } + } else if (out->pend.ref.event_cnt) { + /* Hang out off from conn. */ + talloc_steal(NULL, out); + if (out->buffer != out->default_buffer) + talloc_free(out->buffer); + list_add(&out->list, &conn->ref_list); + out->on_ref_list = true; + return; + } else + domain_outstanding_dec(conn); + talloc_free(out); } @@ -346,6 +383,7 @@ static bool write_messages(struct connec static int destroy_conn(void *_conn) { struct connection *conn = _conn; + struct buffered_data *req; /* Flush outgoing if possible, but don't block. */ if (!conn->domain) { @@ -359,6 +397,11 @@ static int destroy_conn(void *_conn) break; close(conn->fd); } + + conn_free_buffered_data(conn); + list_for_each_entry(req, &conn->ref_list, list) + req->on_ref_list = false; + if (conn->target) talloc_unlink(conn, conn->target); list_del(&conn->list); @@ -798,6 +841,8 @@ void send_reply(struct connection *conn, /* Queue for later transmission. */ list_add_tail(&bdata->list, &conn->out_list); + bdata->on_out_list = true; + domain_outstanding_inc(conn); } /* @@ -805,7 +850,8 @@ void send_reply(struct connection *conn, * As this is not directly related to the current command, errors can't be * reported. */ -void send_event(struct connection *conn, const char *path, const char *token) +void send_event(struct buffered_data *req, struct connection *conn, + const char *path, const char *token) { struct buffered_data *bdata; unsigned int len; @@ -835,8 +881,13 @@ void send_event(struct connection *conn, conn->timeout_msec = bdata->timeout_msec; } + bdata->pend.req = req; + if (req) + req->pend.ref.event_cnt++; + /* Queue for later transmission. */ list_add_tail(&bdata->list, &conn->out_list); + bdata->on_out_list = true; } /* Some routines (write, mkdir, etc) just need a non-error return */ @@ -1572,6 +1623,7 @@ static void handle_input(struct connecti return; } in = conn->in; + in->pend.ref.domid = conn->id; /* Not finished header yet? */ if (in->inhdr) { @@ -1642,6 +1694,7 @@ struct connection *new_connection(connwr new->is_ignored = false; new->transaction_started = 0; INIT_LIST_HEAD(&new->out_list); + INIT_LIST_HEAD(&new->ref_list); INIT_LIST_HEAD(&new->watches); INIT_LIST_HEAD(&new->transaction_list); @@ -2094,6 +2147,9 @@ static void usage(void) " -W, --watch-nb <nb> limit the number of watches per domain,\n" " -t, --transaction <nb> limit the number of transaction allowed per domain,\n" " -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" +" outstanding: number of outstanding requests\n" " -w, --timeout <what>=<seconds> set the timeout in seconds for <what>,\n" " allowed timeout candidates are:\n" " watch-event: time a watch-event is kept pending\n" @@ -2118,6 +2174,7 @@ static struct option options[] = { { "trace-file", 1, NULL, 'T' }, { "transaction", 1, NULL, 't' }, { "perm-nb", 1, NULL, 'A' }, + { "quota", 1, NULL, 'Q' }, { "timeout", 1, NULL, 'w' }, { "no-recovery", 0, NULL, 'R' }, { "internal-db", 0, NULL, 'I' }, @@ -2163,6 +2220,20 @@ static void set_timeout(const char *arg) barf("unknown timeout \"%s\"\n", arg); } +static void set_quota(const char *arg) +{ + const char *eq = strchr(arg, '='); + int val; + + if (!eq) + barf("quotas must be specified via <what>=<nb>\n"); + val = get_optval_int(eq + 1); + if (what_matches(arg, "outstanding")) + quota_req_outstanding = val; + else + barf("unknown quota \"%s\"\n", arg); +} + int main(int argc, char *argv[]) { int opt, *sock = NULL, *ro_sock = NULL; @@ -2174,7 +2245,7 @@ int main(int argc, char *argv[]) int timeout; - while ((opt = getopt_long(argc, argv, "DE:F:HNPS:t:A:T:RVW:w:", options, + while ((opt = getopt_long(argc, argv, "DE:F:HNPS:t:A:Q:T:RVW:w:", options, NULL)) != -1) { switch (opt) { case 'D': @@ -2219,6 +2290,9 @@ int main(int argc, char *argv[]) case 'A': quota_nb_perms_per_node = strtol(optarg, NULL, 10); break; + case 'Q': + set_quota(optarg); + break; case 'w': set_timeout(optarg); break; --- a/tools/xenstore/xenstored_core.h +++ b/tools/xenstore/xenstored_core.h @@ -45,6 +45,8 @@ typedef int32_t wrl_creditt; struct buffered_data { struct list_head list; + bool on_out_list; + bool on_ref_list; /* Are we still doing the header? */ bool inhdr; @@ -52,6 +54,17 @@ struct buffered_data /* How far are we? */ unsigned int used; + /* Outstanding request accounting. */ + union { + /* ref is being used for requests. */ + struct { + unsigned int event_cnt; /* # of outstanding events. */ + unsigned int domid; /* domid of request. */ + } ref; + /* req is being used for watch events. */ + struct buffered_data *req; /* request causing event. */ + } pend; + union { struct xsd_sockmsg msg; char raw[sizeof(struct xsd_sockmsg)]; @@ -93,6 +106,9 @@ struct connection struct list_head out_list; uint64_t timeout_msec; + /* Referenced requests no longer pending. */ + struct list_head ref_list; + /* Transaction context for current request (NULL if none). */ struct transaction *transaction; @@ -154,7 +170,8 @@ unsigned int get_strings(struct buffered void send_reply(struct connection *conn, enum xsd_sockmsg_type type, const void *data, unsigned int len); -void send_event(struct connection *conn, const char *path, const char *token); +void send_event(struct buffered_data *req, struct connection *conn, + const char *path, const char *token); /* Some routines (write, mkdir, etc) just need a non-error return */ void send_ack(struct connection *conn, enum xsd_sockmsg_type type); @@ -202,6 +219,7 @@ extern int dom0_domid; extern int dom0_event; extern int priv_domid; extern int quota_nb_entry_per_domain; +extern int quota_req_outstanding; extern unsigned int timeout_watch_event_msec; --- a/tools/xenstore/xenstored_domain.c +++ b/tools/xenstore/xenstored_domain.c @@ -86,6 +86,9 @@ struct domain /* number of watch for this domain */ int nbwatch; + /* Number of outstanding requests. */ + int nboutstanding; + /* write rate limit */ wrl_creditt wrl_credit; /* [ -wrl_config_writecost, +_dburst ] */ struct wrl_timestampt wrl_timestamp; @@ -296,8 +299,12 @@ bool domain_can_read(struct connection * { struct xenstore_domain_interface *intf = conn->domain->interface; - if (domain_is_unprivileged(conn) && conn->domain->wrl_credit < 0) - return false; + if (domain_is_unprivileged(conn)) { + if (conn->domain->wrl_credit < 0) + return false; + if (conn->domain->nboutstanding >= quota_req_outstanding) + return false; + } if (conn->is_ignored) return false; @@ -346,7 +353,7 @@ static struct domain *alloc_domain(void { struct domain *domain; - domain = talloc(context, struct domain); + domain = talloc_zero(context, struct domain); if (!domain) { errno = ENOMEM; return NULL; @@ -395,8 +402,6 @@ static int new_domain(struct domain *dom domain->conn->id = domain->domid; domain->remote_port = port; - domain->nbentry = 0; - domain->nbwatch = 0; return 0; } @@ -937,6 +942,28 @@ int domain_watch(struct connection *conn : 0; } +void domain_outstanding_inc(struct connection *conn) +{ + if (!conn || !conn->domain) + return; + conn->domain->nboutstanding++; +} + +void domain_outstanding_dec(struct connection *conn) +{ + if (!conn || !conn->domain) + return; + conn->domain->nboutstanding--; +} + +void domain_outstanding_domid_dec(unsigned int domid) +{ + struct domain *d = find_domain_by_domid(domid); + + if (d) + d->nboutstanding--; +} + static wrl_creditt wrl_config_writecost = WRL_FACTOR; static wrl_creditt wrl_config_rate = WRL_RATE * WRL_FACTOR; static wrl_creditt wrl_config_dburst = WRL_DBURST * WRL_FACTOR; --- a/tools/xenstore/xenstored_domain.h +++ b/tools/xenstore/xenstored_domain.h @@ -67,6 +67,9 @@ int domain_entry(struct connection *conn void domain_watch_inc(struct connection *conn); void domain_watch_dec(struct connection *conn); int domain_watch(struct connection *conn); +void domain_outstanding_inc(struct connection *conn); +void domain_outstanding_dec(struct connection *conn); +void domain_outstanding_domid_dec(unsigned int domid); /* Special node permission handling. */ int set_perms_special(struct connection *conn, const char *name, --- a/tools/xenstore/xenstored_watch.c +++ b/tools/xenstore/xenstored_watch.c @@ -142,6 +142,7 @@ void fire_watches(struct connection *con struct node *node, bool exact, struct node_perms *perms) { struct connection *i; + struct buffered_data *req; struct watch *watch; /* During transactions, don't fire watches, but queue them. */ @@ -150,6 +151,8 @@ void fire_watches(struct connection *con return; } + req = domain_is_unprivileged(conn) ? conn->in : NULL; + /* Create an event for each watch. */ list_for_each_entry(i, &connections, list) { /* introduce/release domain watches */ @@ -164,12 +167,12 @@ void fire_watches(struct connection *con list_for_each_entry(watch, &i->watches, list) { if (exact) { if (streq(name, watch->node)) - send_event(i, + send_event(req, i, get_watch_path(watch, name), watch->token); } else { if (is_child(name, watch->node)) - send_event(i, + send_event(req, i, get_watch_path(watch, name), watch->token); } @@ -238,8 +241,12 @@ int do_watch(struct connection *conn, st talloc_set_destructor(watch, destroy_watch); send_ack(conn, XS_WATCH); - /* We fire once up front: simplifies clients and restart. */ - send_event(conn, get_watch_path(watch, watch->node), watch->token); + /* + * We fire once up front: simplifies clients and restart. + * This event will not be linked to the XS_WATCH request. + */ + send_event(NULL, conn, get_watch_path(watch, watch->node), + watch->token); return 0; }
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