[PATCH 15/15] lib/bootconfig: return empty string instead of NULL from xbc_node_get_data()

[Josh Law <objecting@objecting.org>]

xbc_node_get_data() uses WARN_ON (non-fatal) when it detects an
invalid data offset, but returns NULL. Multiple callers pass the
result directly to strlen() or strcmp() without NULL checks, which
would cause a NULL pointer dereference after the non-fatal warning:

  - xbc_node_match_prefix(): strlen(p) on line 197
  - find_match_node(): strcmp(xbc_node_get_data(node), k) on line 644
  - xbc_verify_tree(): strlen(xbc_node_get_data(n)) on lines 832, 853
  - xbc_node_find_next_key_value(): returns NULL to caller on line 404

Return an empty string instead so the WARN_ON remains non-fatal as
intended. The warning backtrace still signals corruption, but the
kernel won't crash in the callers.

Signed-off-by: Josh Law <objecting@objecting.org>
---
 lib/bootconfig.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index 0823491221f4..fae4e6790f34 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -179,14 +179,14 @@ struct xbc_node * __init xbc_node_get_next(struct xbc_node *node)
  * @node: An XBC node.
  *
  * Return the data (which is always a null terminated string) of @node.
- * If the node has invalid data, warn and return NULL.
+ * If the node has invalid data, warn and return an empty string.
  */
 const char * __init xbc_node_get_data(struct xbc_node *node)
 {
 	int offset = node->data & ~XBC_VALUE;
 
 	if (WARN_ON(offset >= xbc_data_size))
-		return NULL;
+		return "";
 
 	return xbc_data + offset;
 }
-- 
2.34.1