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From 074b32e47174a30bb751f2e2c07628eb56117eb8 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Tue, 13 Sep 2022 07:35:11 +0200
Subject: [PATCH 72/87] tools/xenstore: remove recursion from construct_node()
In order to reduce stack usage due to recursion, switch
construct_node() to use a loop instead.
This is part of XSA-418 / CVE-2022-42321.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
(cherry picked from commit da8ee25d02a5447ba39a9800ee2a710ae1f54222)
---
tools/xenstore/xenstored_core.c | 86 +++++++++++++++++++++------------
1 file changed, 55 insertions(+), 31 deletions(-)
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index c676ee4e4e4f..3907c35643e9 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -1377,45 +1377,69 @@ static int add_child(const void *ctx, struct node *parent, const char *name)
static struct node *construct_node(struct connection *conn, const void *ctx,
const char *name)
{
- struct node *parent, *node;
- char *parentname = get_parent(ctx, name);
+ const char **names = NULL;
+ unsigned int levels = 0;
+ struct node *node = NULL;
+ struct node *parent = NULL;
+ const char *parentname = talloc_strdup(ctx, name);
if (!parentname)
return NULL;
- /* If parent doesn't exist, create it. */
- parent = read_node(conn, parentname, parentname);
- if (!parent && errno == ENOENT)
- parent = construct_node(conn, ctx, parentname);
- if (!parent)
- return NULL;
+ /* Walk the path up until an existing node is found. */
+ while (!parent) {
+ names = talloc_realloc(ctx, names, const char *, levels + 1);
+ if (!names)
+ goto nomem;
- /* Add child to parent. */
- if (add_child(ctx, parent, name))
- goto nomem;
+ /*
+ * names[0] is the name of the node to construct initially,
+ * names[1] is its parent, and so on.
+ */
+ names[levels] = parentname;
+ parentname = get_parent(ctx, parentname);
+ if (!parentname)
+ return NULL;
- /* Allocate node */
- node = talloc(ctx, struct node);
- if (!node)
- goto nomem;
- node->name = talloc_strdup(node, name);
- if (!node->name)
- goto nomem;
+ /* Try to read parent node until we found an existing one. */
+ parent = read_node(conn, ctx, parentname);
+ if (!parent && (errno != ENOENT || !strcmp(parentname, "/")))
+ return NULL;
- /* Inherit permissions, except unprivileged domains own what they create */
- node->perms.num = parent->perms.num;
- node->perms.p = talloc_memdup(node, parent->perms.p,
- node->perms.num * sizeof(*node->perms.p));
- if (!node->perms.p)
- goto nomem;
- if (domain_is_unprivileged(conn))
- node->perms.p[0].id = conn->id;
+ levels++;
+ }
+
+ /* Walk the path down again constructing the missing nodes. */
+ for (; levels > 0; levels--) {
+ /* Add child to parent. */
+ if (add_child(ctx, parent, names[levels - 1]))
+ goto nomem;
+
+ /* Allocate node */
+ node = talloc(ctx, struct node);
+ if (!node)
+ goto nomem;
+ node->name = talloc_steal(node, names[levels - 1]);
+
+ /* Inherit permissions, unpriv domains own what they create. */
+ node->perms.num = parent->perms.num;
+ node->perms.p = talloc_memdup(node, parent->perms.p,
+ node->perms.num *
+ sizeof(*node->perms.p));
+ if (!node->perms.p)
+ goto nomem;
+ if (domain_is_unprivileged(conn))
+ node->perms.p[0].id = conn->id;
+
+ /* No children, no data */
+ node->children = node->data = NULL;
+ node->childlen = node->datalen = 0;
+ node->acc.memory = 0;
+ node->parent = parent;
+
+ parent = node;
+ }
- /* No children, no data */
- node->children = node->data = NULL;
- node->childlen = node->datalen = 0;
- node->acc.memory = 0;
- node->parent = parent;
return node;
nomem:
--
2.37.4
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