[PATCH 5.15 282/317] kconfig: fix infinite loop when expanding a macro at the end of file

[Sasha Levin]

From: Masahiro Yamada <masahiroy@xxxxxxxxxx>

[ Upstream commit af8bbce92044dc58e4cc039ab94ee5d470a621f5 ]

A macro placed at the end of a file with no newline causes an infinite
loop.

[Test Kconfig]
  $(info,hello)
  \ No newline at end of file

I realized that flex-provided input() returns 0 instead of EOF when it
reaches the end of a file.

Fixes: 104daea149c4 ("kconfig: reference environment variables directly and remove 'option env='")
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 scripts/kconfig/lexer.l | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/scripts/kconfig/lexer.l b/scripts/kconfig/lexer.l
index 312cbad2d34d4..2a76393d52b5b 100644
--- a/scripts/kconfig/lexer.l
+++ b/scripts/kconfig/lexer.l
@@ -301,8 +301,11 @@ static char *expand_token(const char *in, size_t n)
 	new_string();
 	append_string(in, n);
 
-	/* get the whole line because we do not know the end of token. */
-	while ((c = input()) != EOF) {
+	/*
+	 * get the whole line because we do not know the end of token.
+	 * input() returns 0 (not EOF!) when it reachs the end of file.
+	 */
+	while ((c = input()) != 0) {
 		if (c == '\n') {
 			unput(c);
 			break;
-- 
2.43.0