kconfig: don't crash on NULL expressions in expr_eq()

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@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

diff --git a/config/expr.c b/config/expr.c
index 77ffff3a053ccb844a0f368ae59661a01bc8444c..9f1de58e9f0c995fba0a0a0cf076be4a18e79ca1 100644 (file)
--- a/config/expr.c
+++ b/config/expr.c
@@ -254,6 +254,13 @@ 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) {