[PATCH 4.9 74/91] kconfig: dont crash on NULL expressions in expr_eq()

[Greg Kroah-Hartman]

From: Thomas Hebb <tommyhebb@xxxxxxxxx>

[ Upstream commit 272a72103012862e3a24ea06635253ead0b6e808 ]

NULL expressions are taken to always be true, as implemented by the
expr_is_yes() macro and by several other functions in expr.c. As such,
they ought to be valid inputs to expr_eq(), which compares two
expressions.

Signed-off-by: Thomas Hebb <tommyhebb@xxxxxxxxx>
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 scripts/kconfig/expr.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/scripts/kconfig/expr.c b/scripts/kconfig/expr.c
index ed29bad1f03a..96420b620963 100644
--- a/scripts/kconfig/expr.c
+++ b/scripts/kconfig/expr.c
@@ -201,6 +201,13 @@ static int expr_eq(struct expr *e1, struct expr *e2)
 {
 	int res, old_count;
 
+	/*
+	 * A NULL expr is taken to be yes, but there's also a different way to
+	 * represent yes. expr_is_yes() checks for either representation.
+	 */
+	if (!e1 || !e2)
+		return expr_is_yes(e1) && expr_is_yes(e2);
+
 	if (e1->type != e2->type)
 		return 0;
 	switch (e1->type) {
-- 
2.20.1