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tools/xenstore: introduce dummy nodes for special watch paths

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Instead of special casing the permission handling and watch event
firing for the special watch paths "@introduceDomain" and
"@releaseDomain", use static dummy nodes added to the data base when
starting Xenstore.

The node accounting needs to reflect that change by adding the special
nodes in the domain_entry_fix() call in setup_structure().

Note that this requires to rework the calls of fire_watches() for the
special events in order to avoid leaking memory.

Move the check for a valid node name from get_node() to
get_node_canonicalized(), as it allows to use get_node() for the
special nodes, too.

In order to avoid read and write accesses to the special nodes use a
special variant for obtaining the current node data for the permission
handling.

This allows to simplify quite some code. In future sub-nodes of the
special nodes will be possible due to this change, allowing more fine
grained permission control of special events for specific domains.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
This commit is contained in:
Juergen Gross authored and Julien Grall committed 2023-01-20 09:23:51 +00:00
1 parent ab5fa21c8d
commit d6bb63924f
5 files changed
+84 -202
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tools/xenstore/xenstored_control.c
-3
View File
@@ -676,9 +676,6 @@ static const char *lu_dump_state(const void *ctx, struct connection *conn)
if (ret)
goto out;
ret = dump_state_connections(fp);
if (ret)
goto out;
ret = dump_state_special_nodes(fp);
if (ret)
goto out;
ret = dump_state_nodes(fp, ctx);
tools/xenstore/xenstored_core.c
+59 -37
View File
@@ -597,12 +597,13 @@ static void get_acc_data(TDB_DATA *key, struct node_account_data *acc)
* Per-transaction nodes need to be accounted for the transaction owner.
* Those nodes are stored in the data base with the transaction generation
* count prepended (e.g. 123/local/domain/...). So testing for the node's
* key not to start with "/" is sufficient.
* key not to start with "/" or "@" is sufficient.
*/
static unsigned int get_acc_domid(struct connection *conn, TDB_DATA *key,
unsigned int domid)
{
return (!conn || key->dptr[0] == '/') ? domid : conn->id;
return (!conn || key->dptr[0] == '/' || key->dptr[0] == '@')
? domid : conn->id;
}
int do_tdb_write(struct connection *conn, TDB_DATA *key, TDB_DATA *data,
@@ -944,10 +945,6 @@ static struct node *get_node(struct connection *conn,
{
struct node *node;
if (!name || !is_valid_nodename(name)) {
errno = EINVAL;
return NULL;
}
node = read_node(conn, ctx, name);
/* If we don't have permission, we don't have node. */
if (node) {
@@ -1236,9 +1233,23 @@ static struct node *get_node_canonicalized(struct connection *conn,
*canonical_name = canonicalize(conn, ctx, name);
if (!*canonical_name)
return NULL;
if (!is_valid_nodename(*canonical_name)) {
errno = EINVAL;
return NULL;
}
return get_node(conn, ctx, *canonical_name, perm);
}
static struct node *get_spec_node(struct connection *conn, const void *ctx,
const char *name, char **canonical_name,
unsigned int perm)
{
if (name[0] == '@')
return get_node(conn, ctx, name, perm);
return get_node_canonicalized(conn, ctx, name, canonical_name, perm);
}
static int send_directory(const void *ctx, struct connection *conn,
struct buffered_data *in)
{
@@ -1723,8 +1734,7 @@ static int do_get_perms(const void *ctx, struct connection *conn,
char *strings;
unsigned int len;
node = get_node_canonicalized(conn, ctx, onearg(in), NULL,
XS_PERM_READ);
node = get_spec_node(conn, ctx, onearg(in), NULL, XS_PERM_READ);
if (!node)
return errno;
@@ -1766,17 +1776,9 @@ static int do_set_perms(const void *ctx, struct connection *conn,
if (perms.p[0].perms & XS_PERM_IGNORE)
return ENOENT;
/* First arg is node name. */
if (strstarts(in->buffer, "@")) {
if (set_perms_special(conn, in->buffer, &perms))
return errno;
send_ack(conn, XS_SET_PERMS);
return 0;
}
/* We must own node to do this (tools can do this too). */
node = get_node_canonicalized(conn, ctx, in->buffer, &name,
XS_PERM_WRITE | XS_PERM_OWNER);
node = get_spec_node(conn, ctx, in->buffer, &name,
XS_PERM_WRITE | XS_PERM_OWNER);
if (!node)
return errno;
@@ -2374,7 +2376,9 @@ void setup_structure(bool live_update)
manual_node("/", "tool");
manual_node("/tool", "xenstored");
manual_node("/tool/xenstored", NULL);
domain_entry_fix(dom0_domid, 3, true);
manual_node("@releaseDomain", NULL);
manual_node("@introduceDomain", NULL);
domain_entry_fix(dom0_domid, 5, true);
}
check_store();
@@ -3156,6 +3160,23 @@ static int dump_state_node(const void *ctx, struct connection *conn,
return WALK_TREE_OK;
}
static int dump_state_special_node(FILE *fp, const void *ctx,
struct dump_node_data *data,
const char *name)
{
struct node *node;
int ret;
node = read_node(NULL, ctx, name);
if (!node)
return dump_state_node_err(data, "Dump node read node error");
ret = dump_state_node(ctx, NULL, node, data);
talloc_free(node);
return ret;
}
const char *dump_state_nodes(FILE *fp, const void *ctx)
{
struct dump_node_data data = {
@@ -3167,6 +3188,11 @@ const char *dump_state_nodes(FILE *fp, const void *ctx)
if (walk_node_tree(ctx, NULL, "/", &walkfuncs, &data))
return data.err;
if (dump_state_special_node(fp, ctx, &data, "@releaseDomain"))
return data.err;
if (dump_state_special_node(fp, ctx, &data, "@introduceDomain"))
return data.err;
return NULL;
}
@@ -3340,26 +3366,22 @@ void read_state_node(const void *ctx, const void *state)
node->perms.p[i].id = sn->perms[i].domid;
}
if (strstarts(name, "@")) {
set_perms_special(&conn, name, &node->perms);
talloc_free(node);
return;
if (!strstarts(name, "@")) {
parentname = get_parent(node, name);
if (!parentname)
barf("allocation error restoring node");
parent = read_node(NULL, node, parentname);
if (!parent)
barf("read parent error restoring node");
if (add_child(node, parent, name))
barf("allocation error restoring node");
set_tdb_key(parentname, &key);
if (write_node_raw(NULL, &key, parent, true))
barf("write parent error restoring node");
}
parentname = get_parent(node, name);
if (!parentname)
barf("allocation error restoring node");
parent = read_node(NULL, node, parentname);
if (!parent)
barf("read parent error restoring node");
if (add_child(node, parent, name))
barf("allocation error restoring node");
set_tdb_key(parentname, &key);
if (write_node_raw(NULL, &key, parent, true))
barf("write parent error restoring node");
set_tdb_key(name, &key);
if (write_node_raw(NULL, &key, node, true))
barf("write node error restoring node");
tools/xenstore/xenstored_domain.c
+23 -141
View File
@@ -43,9 +43,6 @@ static evtchn_port_t virq_port;
xenevtchn_handle *xce_handle = NULL;
static struct node_perms dom_release_perms;
static struct node_perms dom_introduce_perms;
struct domain
{
/* The id of this domain */
@@ -225,27 +222,6 @@ static void unmap_interface(void *interface)
xengnttab_unmap(*xgt_handle, interface, 1);
}
static void remove_domid_from_perm(struct node_perms *perms,
struct domain *domain)
{
unsigned int cur, new;
if (perms->p[0].id == domain->domid)
perms->p[0].id = priv_domid;
for (cur = new = 1; cur < perms->num; cur++) {
if (perms->p[cur].id == domain->domid)
continue;
if (new != cur)
perms->p[new] = perms->p[cur];
new++;
}
perms->num = new;
}
static int domain_tree_remove_sub(const void *ctx, struct connection *conn,
struct node *node, void *arg)
{
@@ -297,8 +273,26 @@ static void domain_tree_remove(struct domain *domain)
"error when looking for orphaned nodes\n");
}
remove_domid_from_perm(&dom_release_perms, domain);
remove_domid_from_perm(&dom_introduce_perms, domain);
walk_node_tree(domain, NULL, "@releaseDomain", &walkfuncs, domain);
walk_node_tree(domain, NULL, "@introduceDomain", &walkfuncs, domain);
}
static void fire_special_watches(const char *name)
{
void *ctx = talloc_new(NULL);
struct node *node;
if (!ctx)
return;
node = read_node(NULL, ctx, name);
if (node)
fire_watches(NULL, ctx, name, node, true, NULL);
else
log("special node %s not found\n", name);
talloc_free(ctx);
}
static int destroy_domain(void *_domain)
@@ -326,7 +320,7 @@ static int destroy_domain(void *_domain)
unmap_interface(domain->interface);
}
fire_watches(NULL, domain, "@releaseDomain", NULL, true, NULL);
fire_special_watches("@releaseDomain");
wrl_domain_destroy(domain);
@@ -384,7 +378,7 @@ void check_domains(void)
;
if (notify)
fire_watches(NULL, NULL, "@releaseDomain", NULL, true, NULL);
fire_special_watches("@releaseDomain");
}
/* We scan all domains rather than use the information given here. */
@@ -633,8 +627,7 @@ static struct domain *introduce_domain(const void *ctx,
}
if (!is_master_domain && !restore)
fire_watches(NULL, ctx, "@introduceDomain", NULL,
true, NULL);
fire_special_watches("@introduceDomain");
} else {
/* Use XS_INTRODUCE for recreating the xenbus event-channel. */
if (domain->port)
@@ -840,59 +833,6 @@ const char *get_implicit_path(const struct connection *conn)
return conn->domain->path;
}
static int set_dom_perms_default(struct node_perms *perms)
{
perms->num = 1;
perms->p = talloc_array(NULL, struct xs_permissions, perms->num);
if (!perms->p)
return -1;
perms->p->id = 0;
perms->p->perms = XS_PERM_NONE;
return 0;
}
static struct node_perms *get_perms_special(const char *name)
{
if (!strcmp(name, "@releaseDomain"))
return &dom_release_perms;
if (!strcmp(name, "@introduceDomain"))
return &dom_introduce_perms;
return NULL;
}
int set_perms_special(struct connection *conn, const char *name,
struct node_perms *perms)
{
struct node_perms *p;
p = get_perms_special(name);
if (!p)
return EINVAL;
if ((perm_for_conn(conn, p) & (XS_PERM_WRITE | XS_PERM_OWNER)) !=
(XS_PERM_WRITE | XS_PERM_OWNER))
return EACCES;
p->num = perms->num;
talloc_free(p->p);
p->p = perms->p;
talloc_steal(NULL, perms->p);
return 0;
}
bool check_perms_special(const char *name, struct connection *conn)
{
struct node_perms *p;
p = get_perms_special(name);
if (!p)
return false;
return perm_for_conn(conn, p) & XS_PERM_READ;
}
void dom0_init(void)
{
evtchn_port_t port;
@@ -962,10 +902,6 @@ void domain_init(int evtfd)
if (xce_handle == NULL)
barf_perror("Failed to open evtchn device");
if (set_dom_perms_default(&dom_release_perms) ||
set_dom_perms_default(&dom_introduce_perms))
barf_perror("Failed to set special permissions");
if ((rc = xenevtchn_bind_virq(xce_handle, VIRQ_DOM_EXC)) == -1)
barf_perror("Failed to bind to domain exception virq port");
virq_port = rc;
@@ -1535,60 +1471,6 @@ const char *dump_state_connections(FILE *fp)
return ret;
}
static const char *dump_state_special_node(FILE *fp, const char *name,
const struct node_perms *perms)
{
struct xs_state_record_header head;
struct xs_state_node sn;
unsigned int pathlen;
const char *ret;
pathlen = strlen(name) + 1;
head.type = XS_STATE_TYPE_NODE;
head.length = sizeof(sn);
sn.conn_id = 0;
sn.ta_id = 0;
sn.ta_access = 0;
sn.perm_n = perms->num;
sn.path_len = pathlen;
sn.data_len = 0;
head.length += perms->num * sizeof(*sn.perms);
head.length += pathlen;
head.length = ROUNDUP(head.length, 3);
if (fwrite(&head, sizeof(head), 1, fp) != 1)
return "Dump special node error";
if (fwrite(&sn, sizeof(sn), 1, fp) != 1)
return "Dump special node error";
ret = dump_state_node_perms(fp, perms->p, perms->num);
if (ret)
return ret;
if (fwrite(name, pathlen, 1, fp) != 1)
return "Dump special node path error";
ret = dump_state_align(fp);
return ret;
}
const char *dump_state_special_nodes(FILE *fp)
{
const char *ret;
ret = dump_state_special_node(fp, "@releaseDomain",
&dom_release_perms);
if (ret)
return ret;
ret = dump_state_special_node(fp, "@introduceDomain",
&dom_introduce_perms);
return ret;
}
void read_state_connection(const void *ctx, const void *state)
{
const struct xs_state_connection *sc = state;
tools/xenstore/xenstored_domain.h
-6
View File
@@ -99,11 +99,6 @@ void domain_outstanding_domid_dec(unsigned int domid);
int domain_get_quota(const void *ctx, struct connection *conn,
unsigned int domid);
/* Special node permission handling. */
int set_perms_special(struct connection *conn, const char *name,
struct node_perms *perms);
bool check_perms_special(const char *name, struct connection *conn);
/* Write rate limiting */
#define WRL_FACTOR 1000 /* for fixed-point arithmetic */
@@ -132,7 +127,6 @@ void wrl_apply_debit_direct(struct connection *conn);
void wrl_apply_debit_trans_commit(struct connection *conn);
const char *dump_state_connections(FILE *fp);
const char *dump_state_special_nodes(FILE *fp);
void read_state_connection(const void *ctx, const void *state);
tools/xenstore/xenstored_watch.c
+2 -15
View File
@@ -46,13 +46,6 @@ struct watch
char *node;
};
static bool check_special_event(const char *name)
{
assert(name);
return strstarts(name, "@");
}
/* Is child a subnode of parent, or equal? */
static bool is_child(const char *child, const char *parent)
{
@@ -153,14 +146,8 @@ void fire_watches(struct connection *conn, const void *ctx, const char *name,
/* Create an event for each watch. */
list_for_each_entry(i, &connections, list) {
/* introduce/release domain watches */
if (check_special_event(name)) {
if (!check_perms_special(name, i))
continue;
} else {
if (!watch_permitted(i, ctx, name, node, perms))
continue;
}
if (!watch_permitted(i, ctx, name, node, perms))
continue;
list_for_each_entry(watch, &i->watches, list) {
if (exact) {
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