[PATCH v2 2/3] lib/bootconfig: check bounds before writing in __xbc_open_brace()

[Josh Law <hlcj1234567@gmail.com>]

From: Josh Law <objecting@objecting.org>

The bounds check for brace_index happens after the array write.
While the current call pattern prevents an actual out-of-bounds
access (the previous call would have returned an error), the
write-before-check pattern is fragile and would become a real
out-of-bounds write if the error return were ever not propagated.

Move the bounds check before the array write so the function is
self-contained and safe regardless of caller behavior.

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

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index a1e6a2e14b01..62b4ed7a0ba6 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -532,9 +532,9 @@ static char *skip_spaces_until_newline(char *p)
 static int __init __xbc_open_brace(char *p)
 {
 	/* Push the last key as open brace */
-	open_brace[brace_index++] = xbc_node_index(last_parent);
 	if (brace_index >= XBC_DEPTH_MAX)
 		return xbc_parse_error("Exceed max depth of braces", p);
+	open_brace[brace_index++] = xbc_node_index(last_parent);
 
 	return 0;
 }
-- 
2.34.1