[PATCH][next] kobject: fix dereference before null check on kobj

[PATCH][next] kobject: fix dereference before null check on kobj

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

The kobj pointer is being null-checked so potentially it could be null,
however, the ktype declaration before the null check is dereferencing kobj
hence we have a potential null pointer deference. Fix this by moving the
assignment of ktype after kobj has been null checked.

Addresses-Coverity: ("Dereference before null check")
Fixes: aa30f47cf666 ("kobject: Add support for default attribute groups to kobj_type")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 lib/kobject.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/kobject.c b/lib/kobject.c
index a30ee0467942..095bcb55c2ba 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -603,12 +603,13 @@ EXPORT_SYMBOL_GPL(kobject_move);
 void kobject_del(struct kobject *kobj)
 {
 	struct kernfs_node *sd;
-	const struct kobj_type *ktype = get_ktype(kobj);
+	const struct kobj_type *ktype;
 
 	if (!kobj)
 		return;
 
 	sd = kobj->sd;
+	ktype = get_ktype(kobj);
 
 	if (ktype)
 		sysfs_remove_groups(kobj, ktype->default_groups);
-- 
2.20.1

Re: [PATCH][next] kobject: fix dereference before null check on kobj

[Greg Kroah-Hartman]

On Wed, May 01, 2019 at 01:43:17PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> The kobj pointer is being null-checked so potentially it could be null,
> however, the ktype declaration before the null check is dereferencing kobj
> hence we have a potential null pointer deference. Fix this by moving the
> assignment of ktype after kobj has been null checked.
> 
> Addresses-Coverity: ("Dereference before null check")
> Fixes: aa30f47cf666 ("kobject: Add support for default attribute groups to kobj_type")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  lib/kobject.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Nice catch, thanks, will go queue this up now.

greg k-h