lib/bootconfig: use signed type for offset in xbc_init_node()

  lib/bootconfig.c:415:32: warning: conversion to 'long unsigned int'
  from 'long int' may change the sign of the result [-Wsign-conversion]

Pointer subtraction yields ptrdiff_t (signed), which was stored in
unsigned long.  The original unsigned type implicitly caught a negative
offset (data < xbc_data) because the wrapped value would exceed
XBC_DATA_MAX.  Make this intent explicit by using a signed long and
adding an offset < 0 check to the WARN_ON condition.

Link: https://lore.kernel.org/all/20260318155919.78168-12-objecting@objecting.org/
Signed-off-by: Josh Law <objecting@objecting.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index 9f059bb68e4102b2176c8d7c75827302408effa8..1f84748607b4206c376dbac8f18abb9d9e58bbb3 100644 (file)
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -412,9 +412,9 @@ const char * __init xbc_node_find_next_key_value(struct xbc_node *root,
 
 static int __init xbc_init_node(struct xbc_node *node, char *data, uint16_t flag)
 {
-       unsigned long offset = data - xbc_data;
+       long offset = data - xbc_data;
 
-       if (WARN_ON(offset >= XBC_DATA_MAX))
+       if (WARN_ON(offset < 0 || offset >= XBC_DATA_MAX))
                return -EINVAL;
 
        node->data = (uint16_t)offset | flag;