Move the xbc_node_num increment to after xbc_init_node() so a failed
init does not leave a partially initialized node counted in the array.

If xbc_init_node() fails on a data offset at the boundary of a
maximum-size bootconfig, the pre-incremented count causes subsequent
tree verification and traversal to consider the uninitialized node as
valid, potentially leading to an out-of-bounds read or unpredictable
boot behavior.

Signed-off-by: Josh Law <objecting@objecting.org>
---
 lib/bootconfig.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index ca668ead1db6..6b899e24189c 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -429,9 +429,10 @@ static struct xbc_node * __init xbc_add_node(char *data, uint16_t flag)
 	if (xbc_node_num == XBC_NODE_MAX)
 		return NULL;
 
-	node = &xbc_nodes[xbc_node_num++];
+	node = &xbc_nodes[xbc_node_num];
 	if (xbc_init_node(node, data, flag) < 0)
 		return NULL;
+	xbc_node_num++;
 
 	return node;
 }
-- 
2.34.1