From 1a58ffef993fe86fe8a7c1349881650e9b0fe8a7 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Tue, 13 Sep 2022 07:35:10 +0200
Subject: tools/xenstore: don't use conn->in as context for temporary
 allocations

Using the struct buffered data pointer of the current processed request
for temporary data allocations has a major drawback: the used area (and
with that the temporary data) is freed only after the response of the
request has been written to the ring page or has been read via the
socket. This can happen much later in case a guest isn't reading its
responses fast enough.

As the temporary data can be safely freed after creating the response,
add a temporary context for that purpose and use that for allocating
the temporary memory, as it was already the case before commit
cc0612464896 ("xenstore: add small default data buffer to internal
struct").

Some sub-functions need to gain the "const" attribute for the talloc
context.

This is XSA-416 / CVE-2022-42319.

Reported-by: Julien Grall <jgrall@amazon.com>
Fixes: cc0612464896 ("xenstore: add small default data buffer to internal struct")
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>

diff --git a/tools/xenstore/xenstored_control.c b/tools/xenstore/xenstored_control.c
index 454fe9d5ab18..3585d7c6950d 100644
--- a/tools/xenstore/xenstored_control.c
+++ b/tools/xenstore/xenstored_control.c
@@ -30,11 +30,11 @@
 
 struct cmd_s {
 	char *cmd;
-	int (*func)(void *, struct connection *, char **, int);
+	int (*func)(const void *, struct connection *, char **, int);
 	char *pars;
 };
 
-static int do_control_check(void *ctx, struct connection *conn,
+static int do_control_check(const void *ctx, struct connection *conn,
 			    char **vec, int num)
 {
 	if (num)
@@ -46,7 +46,7 @@ static int do_control_check(void *ctx, struct connection *conn,
 	return 0;
 }
 
-static int do_control_log(void *ctx, struct connection *conn,
+static int do_control_log(const void *ctx, struct connection *conn,
 			  char **vec, int num)
 {
 	if (num != 1)
@@ -63,7 +63,7 @@ static int do_control_log(void *ctx, struct connection *conn,
 	return 0;
 }
 
-static int do_control_logfile(void *ctx, struct connection *conn,
+static int do_control_logfile(const void *ctx, struct connection *conn,
 			      char **vec, int num)
 {
 	if (num != 1)
@@ -162,7 +162,7 @@ static int quota_get(const void *ctx, struct connection *conn,
 	return domain_get_quota(ctx, conn, atoi(vec[0]));
 }
 
-static int do_control_quota(void *ctx, struct connection *conn,
+static int do_control_quota(const void *ctx, struct connection *conn,
 			    char **vec, int num)
 {
 	if (num == 0)
@@ -174,7 +174,7 @@ static int do_control_quota(void *ctx, struct connection *conn,
 	return quota_get(ctx, conn, vec, num);
 }
 
-static int do_control_quota_s(void *ctx, struct connection *conn,
+static int do_control_quota_s(const void *ctx, struct connection *conn,
 			      char **vec, int num)
 {
 	if (num == 0)
@@ -186,7 +186,7 @@ static int do_control_quota_s(void *ctx, struct connection *conn,
 	return EINVAL;
 }
 
-static int do_control_memreport(void *ctx, struct connection *conn,
+static int do_control_memreport(const void *ctx, struct connection *conn,
 				char **vec, int num)
 {
 	FILE *fp;
@@ -225,7 +225,7 @@ static int do_control_memreport(void *ctx, struct connection *conn,
 	return 0;
 }
 
-static int do_control_print(void *ctx, struct connection *conn,
+static int do_control_print(const void *ctx, struct connection *conn,
 			    char **vec, int num)
 {
 	if (num != 1)
@@ -237,7 +237,7 @@ static int do_control_print(void *ctx, struct connection *conn,
 	return 0;
 }
 
-static int do_control_help(void *, struct connection *, char **, int);
+static int do_control_help(const void *, struct connection *, char **, int);
 
 static struct cmd_s cmds[] = {
 	{ "check", do_control_check, "" },
@@ -250,7 +250,7 @@ static struct cmd_s cmds[] = {
 	{ "help", do_control_help, "" },
 };
 
-static int do_control_help(void *ctx, struct connection *conn,
+static int do_control_help(const void *ctx, struct connection *conn,
 			   char **vec, int num)
 {
 	int cmd, len = 0;
@@ -286,7 +286,8 @@ static int do_control_help(void *ctx, struct connection *conn,
 	return 0;
 }
 
-int do_control(struct connection *conn, struct buffered_data *in)
+int do_control(const void *ctx, struct connection *conn,
+	       struct buffered_data *in)
 {
 	int num;
 	int cmd;
@@ -298,7 +299,7 @@ int do_control(struct connection *conn, struct buffered_data *in)
 	num = xs_count_strings(in->buffer, in->used);
 	if (num < 1)
 		return EINVAL;
-	vec = talloc_array(in, char *, num);
+	vec = talloc_array(ctx, char *, num);
 	if (!vec)
 		return ENOMEM;
 	if (get_strings(in, vec, num) != num)
@@ -306,7 +307,7 @@ int do_control(struct connection *conn, struct buffered_data *in)
 
 	for (cmd = 0; cmd < ARRAY_SIZE(cmds); cmd++)
 		if (streq(vec[0], cmds[cmd].cmd))
-			return cmds[cmd].func(in, conn, vec + 1, num - 1);
+			return cmds[cmd].func(ctx, conn, vec + 1, num - 1);
 
 	return EINVAL;
 }
diff --git a/tools/xenstore/xenstored_control.h b/tools/xenstore/xenstored_control.h
index 207e0a6fa352..faa955968db1 100644
--- a/tools/xenstore/xenstored_control.h
+++ b/tools/xenstore/xenstored_control.h
@@ -16,4 +16,5 @@
     along with this program; If not, see <http://www.gnu.org/licenses/>.
 */
 
-int do_control(struct connection *conn, struct buffered_data *in);
+int do_control(const void *ctx, struct connection *conn,
+	       struct buffered_data *in);
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 2c0f8fd99bbd..d6bbb532fb18 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -1145,11 +1145,13 @@ static struct node *get_node_canonicalized(struct connection *conn,
 	return get_node(conn, ctx, *canonical_name, perm);
 }
 
-static int send_directory(struct connection *conn, struct buffered_data *in)
+static int send_directory(const void *ctx, struct connection *conn,
+			  struct buffered_data *in)
 {
 	struct node *node;
 
-	node = get_node_canonicalized(conn, in, onearg(in), NULL, XS_PERM_READ);
+	node = get_node_canonicalized(conn, ctx, onearg(in), NULL,
+				      XS_PERM_READ);
 	if (!node)
 		return errno;
 
@@ -1158,7 +1160,7 @@ static int send_directory(struct connection *conn, struct buffered_data *in)
 	return 0;
 }
 
-static int send_directory_part(struct connection *conn,
+static int send_directory_part(const void *ctx, struct connection *conn,
 			       struct buffered_data *in)
 {
 	unsigned int off, len, maxlen, genlen;
@@ -1170,7 +1172,8 @@ static int send_directory_part(struct connection *conn,
 		return EINVAL;
 
 	/* First arg is node name. */
-	node = get_node_canonicalized(conn, in, in->buffer, NULL, XS_PERM_READ);
+	node = get_node_canonicalized(conn, ctx, in->buffer, NULL,
+				      XS_PERM_READ);
 	if (!node)
 		return errno;
 
@@ -1197,7 +1200,7 @@ static int send_directory_part(struct connection *conn,
 			break;
 	}
 
-	data = talloc_array(in, char, genlen + len + 1);
+	data = talloc_array(ctx, char, genlen + len + 1);
 	if (!data)
 		return ENOMEM;
 
@@ -1213,11 +1216,13 @@ static int send_directory_part(struct connection *conn,
 	return 0;
 }
 
-static int do_read(struct connection *conn, struct buffered_data *in)
+static int do_read(const void *ctx, struct connection *conn,
+		   struct buffered_data *in)
 {
 	struct node *node;
 
-	node = get_node_canonicalized(conn, in, onearg(in), NULL, XS_PERM_READ);
+	node = get_node_canonicalized(conn, ctx, onearg(in), NULL,
+				      XS_PERM_READ);
 	if (!node)
 		return errno;
 
@@ -1397,7 +1402,8 @@ static struct node *create_node(struct connection *conn, const void *ctx,
 }
 
 /* path, data... */
-static int do_write(struct connection *conn, struct buffered_data *in)
+static int do_write(const void *ctx, struct connection *conn,
+		    struct buffered_data *in)
 {
 	unsigned int offset, datalen;
 	struct node *node;
@@ -1411,12 +1417,12 @@ static int do_write(struct connection *conn, struct buffered_data *in)
 	offset = strlen(vec[0]) + 1;
 	datalen = in->used - offset;
 
-	node = get_node_canonicalized(conn, in, vec[0], &name, XS_PERM_WRITE);
+	node = get_node_canonicalized(conn, ctx, vec[0], &name, XS_PERM_WRITE);
 	if (!node) {
 		/* No permissions, invalid input? */
 		if (errno != ENOENT)
 			return errno;
-		node = create_node(conn, in, name, in->buffer + offset,
+		node = create_node(conn, ctx, name, in->buffer + offset,
 				   datalen);
 		if (!node)
 			return errno;
@@ -1427,18 +1433,19 @@ static int do_write(struct connection *conn, struct buffered_data *in)
 			return errno;
 	}
 
-	fire_watches(conn, in, name, node, false, NULL);
+	fire_watches(conn, ctx, name, node, false, NULL);
 	send_ack(conn, XS_WRITE);
 
 	return 0;
 }
 
-static int do_mkdir(struct connection *conn, struct buffered_data *in)
+static int do_mkdir(const void *ctx, struct connection *conn,
+		    struct buffered_data *in)
 {
 	struct node *node;
 	char *name;
 
-	node = get_node_canonicalized(conn, in, onearg(in), &name,
+	node = get_node_canonicalized(conn, ctx, onearg(in), &name,
 				      XS_PERM_WRITE);
 
 	/* If it already exists, fine. */
@@ -1446,10 +1453,10 @@ static int do_mkdir(struct connection *conn, struct buffered_data *in)
 		/* No permissions? */
 		if (errno != ENOENT)
 			return errno;
-		node = create_node(conn, in, name, NULL, 0);
+		node = create_node(conn, ctx, name, NULL, 0);
 		if (!node)
 			return errno;
-		fire_watches(conn, in, name, node, false, NULL);
+		fire_watches(conn, ctx, name, node, false, NULL);
 	}
 	send_ack(conn, XS_MKDIR);
 
@@ -1547,22 +1554,23 @@ static int _rm(struct connection *conn, const void *ctx, struct node *node,
 }
 
 
-static int do_rm(struct connection *conn, struct buffered_data *in)
+static int do_rm(const void *ctx, struct connection *conn,
+		 struct buffered_data *in)
 {
 	struct node *node;
 	int ret;
 	char *name;
 	char *parentname;
 
-	node = get_node_canonicalized(conn, in, onearg(in), &name,
+	node = get_node_canonicalized(conn, ctx, onearg(in), &name,
 				      XS_PERM_WRITE);
 	if (!node) {
 		/* Didn't exist already?  Fine, if parent exists. */
 		if (errno == ENOENT) {
-			parentname = get_parent(in, name);
+			parentname = get_parent(ctx, name);
 			if (!parentname)
 				return errno;
-			node = read_node(conn, in, parentname);
+			node = read_node(conn, ctx, parentname);
 			if (node) {
 				send_ack(conn, XS_RM);
 				return 0;
@@ -1577,7 +1585,7 @@ static int do_rm(struct connection *conn, struct buffered_data *in)
 	if (streq(name, "/"))
 		return EINVAL;
 
-	ret = _rm(conn, in, node, name);
+	ret = _rm(conn, ctx, node, name);
 	if (ret)
 		return ret;
 
@@ -1587,13 +1595,15 @@ static int do_rm(struct connection *conn, struct buffered_data *in)
 }
 
 
-static int do_get_perms(struct connection *conn, struct buffered_data *in)
+static int do_get_perms(const void *ctx, struct connection *conn,
+			struct buffered_data *in)
 {
 	struct node *node;
 	char *strings;
 	unsigned int len;
 
-	node = get_node_canonicalized(conn, in, onearg(in), NULL, XS_PERM_READ);
+	node = get_node_canonicalized(conn, ctx, onearg(in), NULL,
+				      XS_PERM_READ);
 	if (!node)
 		return errno;
 
@@ -1606,7 +1616,8 @@ static int do_get_perms(struct connection *conn, struct buffered_data *in)
 	return 0;
 }
 
-static int do_set_perms(struct connection *conn, struct buffered_data *in)
+static int do_set_perms(const void *ctx, struct connection *conn,
+			struct buffered_data *in)
 {
 	struct node_perms perms, old_perms;
 	char *name, *permstr;
@@ -1623,7 +1634,7 @@ static int do_set_perms(struct connection *conn, struct buffered_data *in)
 
 	permstr = in->buffer + strlen(in->buffer) + 1;
 
-	perms.p = talloc_array(in, struct xs_permissions, perms.num);
+	perms.p = talloc_array(ctx, struct xs_permissions, perms.num);
 	if (!perms.p)
 		return ENOMEM;
 	if (!xs_strings_to_perms(perms.p, perms.num, permstr))
@@ -1638,7 +1649,7 @@ static int do_set_perms(struct connection *conn, struct buffered_data *in)
 	}
 
 	/* We must own node to do this (tools can do this too). */
-	node = get_node_canonicalized(conn, in, in->buffer, &name,
+	node = get_node_canonicalized(conn, ctx, in->buffer, &name,
 				      XS_PERM_WRITE | XS_PERM_OWNER);
 	if (!node)
 		return errno;
@@ -1673,7 +1684,7 @@ static int do_set_perms(struct connection *conn, struct buffered_data *in)
 		return errno;
 	}
 
-	fire_watches(conn, in, name, node, false, &old_perms);
+	fire_watches(conn, ctx, name, node, false, &old_perms);
 	send_ack(conn, XS_SET_PERMS);
 
 	return 0;
@@ -1681,7 +1692,8 @@ static int do_set_perms(struct connection *conn, struct buffered_data *in)
 
 static struct {
 	const char *str;
-	int (*func)(struct connection *conn, struct buffered_data *in);
+	int (*func)(const void *ctx, struct connection *conn,
+		    struct buffered_data *in);
 	unsigned int flags;
 #define XS_FLAG_NOTID		(1U << 0)	/* Ignore transaction id. */
 #define XS_FLAG_PRIV		(1U << 1)	/* Privileged domain only. */
@@ -1754,6 +1766,7 @@ static void process_message(struct connection *conn, struct buffered_data *in)
 	struct transaction *trans;
 	enum xsd_sockmsg_type type = in->hdr.msg.type;
 	int ret;
+	void *ctx;
 
 	if ((unsigned int)type >= XS_TYPE_COUNT || !wire_funcs[type].func) {
 		eprintf("Client unknown operation %i", type);
@@ -1774,10 +1787,17 @@ static void process_message(struct connection *conn, struct buffered_data *in)
 		return;
 	}
 
+	ctx = talloc_new(NULL);
+	if (!ctx) {
+		send_error(conn, ENOMEM);
+		return;
+	}
+
 	assert(conn->transaction == NULL);
 	conn->transaction = trans;
 
-	ret = wire_funcs[type].func(conn, in);
+	ret = wire_funcs[type].func(ctx, conn, in);
+	talloc_free(ctx);
 	if (ret)
 		send_error(conn, ret);
 
diff --git a/tools/xenstore/xenstored_domain.c b/tools/xenstore/xenstored_domain.c
index f458314c8e01..04bdf5179227 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -337,7 +337,7 @@ bool domain_can_write(struct connection *conn)
 	return ((intf->rsp_prod - intf->rsp_cons) != XENSTORE_RING_SIZE);
 }
 
-static char *talloc_domain_path(void *context, unsigned int domid)
+static char *talloc_domain_path(const void *context, unsigned int domid)
 {
 	return talloc_asprintf(context, "/local/domain/%u", domid);
 }
@@ -479,7 +479,8 @@ static void domain_conn_reset(struct domain *domain)
 }
 
 /* domid, mfn, evtchn, path */
-int do_introduce(struct connection *conn, struct buffered_data *in)
+int do_introduce(const void *ctx, struct connection *conn,
+		 struct buffered_data *in)
 {
 	struct domain *domain;
 	char *vec[3];
@@ -563,7 +564,8 @@ static struct domain *find_connected_domain(unsigned int domid)
 	return domain;
 }
 
-int do_set_target(struct connection *conn, struct buffered_data *in)
+int do_set_target(const void *ctx, struct connection *conn,
+		  struct buffered_data *in)
 {
 	char *vec[2];
 	unsigned int domid, tdomid;
@@ -610,7 +612,8 @@ static struct domain *onearg_domain(struct connection *conn,
 }
 
 /* domid */
-int do_release(struct connection *conn, struct buffered_data *in)
+int do_release(const void *ctx, struct connection *conn,
+	       struct buffered_data *in)
 {
 	struct domain *domain;
 
@@ -625,7 +628,8 @@ int do_release(struct connection *conn, struct buffered_data *in)
 	return 0;
 }
 
-int do_resume(struct connection *conn, struct buffered_data *in)
+int do_resume(const void *ctx, struct connection *conn,
+	      struct buffered_data *in)
 {
 	struct domain *domain;
 
@@ -640,7 +644,8 @@ int do_resume(struct connection *conn, struct buffered_data *in)
 	return 0;
 }
 
-int do_get_domain_path(struct connection *conn, struct buffered_data *in)
+int do_get_domain_path(const void *ctx, struct connection *conn,
+		       struct buffered_data *in)
 {
 	char *path;
 	const char *domid_str = onearg(in);
@@ -648,18 +653,17 @@ int do_get_domain_path(struct connection *conn, struct buffered_data *in)
 	if (!domid_str)
 		return EINVAL;
 
-	path = talloc_domain_path(conn, atoi(domid_str));
+	path = talloc_domain_path(ctx, atoi(domid_str));
 	if (!path)
 		return errno;
 
 	send_reply(conn, XS_GET_DOMAIN_PATH, path, strlen(path) + 1);
 
-	talloc_free(path);
-
 	return 0;
 }
 
-int do_is_domain_introduced(struct connection *conn, struct buffered_data *in)
+int do_is_domain_introduced(const void *ctx, struct connection *conn,
+			    struct buffered_data *in)
 {
 	int result;
 	unsigned int domid;
@@ -680,7 +684,8 @@ int do_is_domain_introduced(struct connection *conn, struct buffered_data *in)
 }
 
 /* Allow guest to reset all watches */
-int do_reset_watches(struct connection *conn, struct buffered_data *in)
+int do_reset_watches(const void *ctx, struct connection *conn,
+		     struct buffered_data *in)
 {
 	conn_delete_all_watches(conn);
 	conn_delete_all_transactions(conn);
diff --git a/tools/xenstore/xenstored_domain.h b/tools/xenstore/xenstored_domain.h
index e013a9991ca8..732eb8fa75e1 100644
--- a/tools/xenstore/xenstored_domain.h
+++ b/tools/xenstore/xenstored_domain.h
@@ -22,25 +22,32 @@
 void handle_event(void);
 
 /* domid, mfn, eventchn, path */
-int do_introduce(struct connection *conn, struct buffered_data *in);
+int do_introduce(const void *ctx, struct connection *conn,
+		 struct buffered_data *in);
 
 /* domid */
-int do_is_domain_introduced(struct connection *conn, struct buffered_data *in);
+int do_is_domain_introduced(const void *ctx, struct connection *conn,
+			    struct buffered_data *in);
 
 /* domid */
-int do_release(struct connection *conn, struct buffered_data *in);
+int do_release(const void *ctx, struct connection *conn,
+	       struct buffered_data *in);
 
 /* domid */
-int do_resume(struct connection *conn, struct buffered_data *in);
+int do_resume(const void *ctx, struct connection *conn,
+	      struct buffered_data *in);
 
 /* domid, target */
-int do_set_target(struct connection *conn, struct buffered_data *in);
+int do_set_target(const void *ctx, struct connection *conn,
+		  struct buffered_data *in);
 
 /* domid */
-int do_get_domain_path(struct connection *conn, struct buffered_data *in);
+int do_get_domain_path(const void *ctx, struct connection *conn,
+		       struct buffered_data *in);
 
 /* Allow guest to reset all watches */
-int do_reset_watches(struct connection *conn, struct buffered_data *in);
+int do_reset_watches(const void *ctx, struct connection *conn,
+		     struct buffered_data *in);
 
 void domain_init(void);
 
diff --git a/tools/xenstore/xenstored_transaction.c b/tools/xenstore/xenstored_transaction.c
index 6e29118c800d..cd592845e7ca 100644
--- a/tools/xenstore/xenstored_transaction.c
+++ b/tools/xenstore/xenstored_transaction.c
@@ -487,7 +487,8 @@ struct transaction *transaction_lookup(struct connection *conn, uint32_t id)
 	return ERR_PTR(-ENOENT);
 }
 
-int do_transaction_start(struct connection *conn, struct buffered_data *in)
+int do_transaction_start(const void *ctx, struct connection *conn,
+			 struct buffered_data *in)
 {
 	struct transaction *trans, *exists;
 	char id_str[20];
@@ -500,8 +501,8 @@ int do_transaction_start(struct connection *conn, struct buffered_data *in)
 	    conn->transaction_started > quota_max_transaction)
 		return ENOSPC;
 
-	/* Attach transaction to input for autofree until it's complete */
-	trans = talloc_zero(in, struct transaction);
+	/* Attach transaction to ctx for autofree until it's complete */
+	trans = talloc_zero(ctx, struct transaction);
 	if (!trans)
 		return ENOMEM;
 
@@ -548,7 +549,8 @@ static int transaction_fix_domains(struct transaction *trans, bool update)
 	return 0;
 }
 
-int do_transaction_end(struct connection *conn, struct buffered_data *in)
+int do_transaction_end(const void *ctx, struct connection *conn,
+		       struct buffered_data *in)
 {
 	const char *arg = onearg(in);
 	struct transaction *trans;
@@ -564,8 +566,8 @@ int do_transaction_end(struct connection *conn, struct buffered_data *in)
 	list_del(&trans->list);
 	conn->transaction_started--;
 
-	/* Attach transaction to in for auto-cleanup */
-	talloc_steal(in, trans);
+	/* Attach transaction to ctx for auto-cleanup */
+	talloc_steal(ctx, trans);
 
 	if (streq(arg, "T")) {
 		if (trans->fail)
diff --git a/tools/xenstore/xenstored_transaction.h b/tools/xenstore/xenstored_transaction.h
index e3cbd6b23095..39d7f81c5127 100644
--- a/tools/xenstore/xenstored_transaction.h
+++ b/tools/xenstore/xenstored_transaction.h
@@ -29,8 +29,10 @@ struct transaction;
 
 extern uint64_t generation;
 
-int do_transaction_start(struct connection *conn, struct buffered_data *node);
-int do_transaction_end(struct connection *conn, struct buffered_data *in);
+int do_transaction_start(const void *ctx, struct connection *conn,
+			 struct buffered_data *node);
+int do_transaction_end(const void *ctx, struct connection *conn,
+		       struct buffered_data *in);
 
 struct transaction *transaction_lookup(struct connection *conn, uint32_t id);
 
diff --git a/tools/xenstore/xenstored_watch.c b/tools/xenstore/xenstored_watch.c
index 19d0fb01b1c4..13627ce97266 100644
--- a/tools/xenstore/xenstored_watch.c
+++ b/tools/xenstore/xenstored_watch.c
@@ -184,7 +184,7 @@ static int destroy_watch(void *_watch)
 	return 0;
 }
 
-int do_watch(struct connection *conn, struct buffered_data *in)
+int do_watch(const void *ctx, struct connection *conn, struct buffered_data *in)
 {
 	struct watch *watch;
 	char *vec[2];
@@ -200,7 +200,7 @@ int do_watch(struct connection *conn, struct buffered_data *in)
 		/* check if valid event */
 	} else {
 		relative = !strstarts(vec[0], "/");
-		vec[0] = canonicalize(conn, in, vec[0]);
+		vec[0] = canonicalize(conn, ctx, vec[0]);
 		if (!vec[0])
 			return ENOMEM;
 		if (!is_valid_nodename(vec[0]))
@@ -250,7 +250,8 @@ int do_watch(struct connection *conn, struct buffered_data *in)
 	return 0;
 }
 
-int do_unwatch(struct connection *conn, struct buffered_data *in)
+int do_unwatch(const void *ctx, struct connection *conn,
+	       struct buffered_data *in)
 {
 	struct watch *watch;
 	char *node, *vec[2];
@@ -258,7 +259,7 @@ int do_unwatch(struct connection *conn, struct buffered_data *in)
 	if (get_strings(in, vec, ARRAY_SIZE(vec)) != ARRAY_SIZE(vec))
 		return EINVAL;
 
-	node = canonicalize(conn, in, vec[0]);
+	node = canonicalize(conn, ctx, vec[0]);
 	if (!node)
 		return ENOMEM;
 	list_for_each_entry(watch, &conn->watches, list) {
diff --git a/tools/xenstore/xenstored_watch.h b/tools/xenstore/xenstored_watch.h
index 03094374f379..40455dff5d2b 100644
--- a/tools/xenstore/xenstored_watch.h
+++ b/tools/xenstore/xenstored_watch.h
@@ -21,8 +21,10 @@
 
 #include "xenstored_core.h"
 
-int do_watch(struct connection *conn, struct buffered_data *in);
-int do_unwatch(struct connection *conn, struct buffered_data *in);
+int do_watch(const void *ctx, struct connection *conn,
+	     struct buffered_data *in);
+int do_unwatch(const void *ctx, struct connection *conn,
+	       struct buffered_data *in);
 
 /* Fire all watches: !exact means all the children are affected (ie. rm). */
 void fire_watches(struct connection *conn, const void *tmp, const char *name,