[PATCH 3/3] kconfig: Clean up modules handling and fix crash

From: Ulf Magnusson
Date: Thu Oct 05 2017 - 08:03:14 EST

Kconfig currently doesn't handle 'm' appearing in a Kconfig file before
the modules symbol is defined (the symbol with 'option modules'). The
problem is the following code, which runs during parsing:

/* change 'm' into 'm' && MODULES */
if (e->left.sym == &symbol_mod)
return expr_alloc_and(e, expr_alloc_symbol(modules_sym));

If the modules symbol has not yet been defined, modules_sym is NULL,
giving an invalid expression.

Here is a test file where both BEFORE_1 and BEFORE_2 trigger a segfault.
If the modules symbol is removed, all symbols trigger segfaults.

config BEFORE_1
def_tristate y if m

if m
config BEFORE_2
def_tristate y

config MODULES
def_bool y
option modules

config AFTER_1
def_tristate y if m

if m
config AFTER_2
def_tristate y

Fix the issue by rewriting 'm' in menu_finalize() instead. This function
runs after parsing and is the proper place to do it. The following
existing code in conf_parse() in zconf.y ensures that the modules symbol
exists at that point:

if (!modules_sym)
modules_sym = sym_find( "n" );



The following tests were done to ensure no functional changes for
configurations that don't reference 'm' before the modules symbol:

- zconfdump(stdout) was run with ARCH=x86 and ARCH=arm before
and after the change and verified to produce identical output.
This function prints all symbols, choices, and menus together
with their properties and their dependency expressions. A
rewritten 'm' appears as 'm && MODULES'.

A small annoyance is that the assert(len != 0) in xfwrite()
needs to be disabled in order to use zconfdump(), because it
chokes on e.g. 'default ""'.

- The Kconfiglib test suite was run to indirectly verify that
alldefconfig, allyesconfig, allnoconfig, and all defconfigs in
the kernel still generate the same final .config.

- Valgrind was used to check for memory errors and (new) memory

Signed-off-by: Ulf Magnusson <ulfalizer@xxxxxxxxx>
scripts/kconfig/menu.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index 94f192de..a7396e4 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -110,7 +110,7 @@ static struct expr *rewrite_m(struct expr *e)

void menu_add_dep(struct expr *dep)
- current_entry->dep = expr_alloc_and(current_entry->dep, rewrite_m(dep));
+ current_entry->dep = expr_alloc_and(current_entry->dep, dep);

void menu_set_type(int type)
@@ -135,7 +135,7 @@ static struct property *menu_add_prop(enum prop_type type, char *prompt, struct

prop->menu = current_entry;
prop->expr = expr;
- prop->visible.expr = rewrite_m(dep);
+ prop->visible.expr = dep;

if (prompt) {
if (isspace(*prompt)) {
@@ -330,7 +330,8 @@ void menu_finalize(struct menu *parent)
* Propagate parent dependencies to the child menu
* node, also rewriting and simplifying expressions
- basedep = expr_transform(menu->dep);
+ basedep = rewrite_m(menu->dep);
+ basedep = expr_transform(basedep);
basedep = expr_alloc_and(expr_copy(parentdep), basedep);
basedep = expr_eliminate_dups(basedep);
menu->dep = basedep;
@@ -373,7 +374,8 @@ void menu_finalize(struct menu *parent)
* property's condition, rewriting and
* simplifying expressions at the same time
- dep = expr_transform(prop->visible.expr);
+ dep = rewrite_m(prop->visible.expr);
+ dep = expr_transform(dep);
dep = expr_alloc_and(expr_copy(basedep), dep);
dep = expr_eliminate_dups(dep);
if (menu->sym && menu->sym->type != S_TRISTATE)