[PATCH v3 20/25] tools/xenstore: alloc new memory in domain_adjust_node_perms()

[Juergen Gross <jgross@suse.com>]

In order to avoid modifying the node data in the data base in case a
domain is gone, let domain_adjust_node_perms() allocate new memory for
the permissions in case they need to be modified. As this should
happen only in very rare cases, it is fine to do this even when having
copied the node data already.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V3:
- new patch
---
 tools/xenstore/xenstored_core.c   | 10 +++++-----
 tools/xenstore/xenstored_domain.c | 19 +++++++++++++++----
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 404ecd0c62..ea3d20a372 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -751,6 +751,11 @@ struct node *read_node(struct connection *conn, const void *ctx,
 		goto error;
 	}
 
+	/* Data is binary blob (usually ascii, no nul). */
+	node->data = node->perms + hdr->num_perms;
+	/* Children is strings, nul separated. */
+	node->children = node->data + node->hdr.datalen;
+
 	if (domain_adjust_node_perms(node))
 		goto error;
 
@@ -758,11 +763,6 @@ struct node *read_node(struct connection *conn, const void *ctx,
 	if (node->acc.domid != get_node_owner(node))
 		node->acc.memory = 0;
 
-	/* Data is binary blob (usually ascii, no nul). */
-	node->data = node->perms + hdr->num_perms;
-	/* Children is strings, nul separated. */
-	node->children = node->data + node->hdr.datalen;
-
 	if (access_node(conn, node, NODE_ACCESS_READ, NULL))
 		goto error;
 
diff --git a/tools/xenstore/xenstored_domain.c b/tools/xenstore/xenstored_domain.c
index fdf1095acb..cdef6efef4 100644
--- a/tools/xenstore/xenstored_domain.c
+++ b/tools/xenstore/xenstored_domain.c
@@ -1334,13 +1334,24 @@ int domain_alloc_permrefs(struct node_perms *perms)
 int domain_adjust_node_perms(struct node *node)
 {
 	unsigned int i;
+	struct xs_permissions *perms = node->perms;
+	bool copied = false;
 
 	for (i = 1; i < node->hdr.num_perms; i++) {
-		if (node->perms[i].perms & XS_PERM_IGNORE)
+		if ((perms[i].perms & XS_PERM_IGNORE) ||
+		    chk_domain_generation(perms[i].id, node->hdr.generation))
 			continue;
-		if (!chk_domain_generation(node->perms[i].id,
-					   node->hdr.generation))
-			node->perms[i].perms |= XS_PERM_IGNORE;
+
+		if (!copied) {
+			perms = talloc_memdup(node, node->perms,
+					node->hdr.num_perms * sizeof(*perms));
+			if (!perms)
+				return ENOMEM;
+			node->perms = perms;
+			copied = true;
+		}
+
+		perms[i].perms |= XS_PERM_IGNORE;
 	}
 
 	return 0;
-- 
2.35.3