[PATCH] net: fix shift-out-of-bounds in nl802154_new_interface

[PATCH] net: fix shift-out-of-bounds in nl802154_new_interface

[Pavel Skripkin]

syzbot reported shift-out-of-bounds in nl802154_new_interface.
The problem was in signed representation of enum nl802154_iftype

enum nl802154_iftype {
	/* for backwards compatibility TODO */
	NL802154_IFTYPE_UNSPEC = -1,
...

Since, enum has negative value in it, objects of this type
will be represented as signed integer.

	type = nla_get_u32(info->attrs[NL802154_ATTR_IFTYPE]);

u32 will be casted to signed, which can cause negative value type.

Reported-by: syzbot+7bf7b22759195c9a21e9@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---
 net/ieee802154/nl802154.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ieee802154/nl802154.c b/net/ieee802154/nl802154.c
index 7c5a1aa5adb4..6cce045e3d40 100644
--- a/net/ieee802154/nl802154.c
+++ b/net/ieee802154/nl802154.c
@@ -910,7 +910,7 @@ static int nl802154_new_interface(struct sk_buff *skb, struct genl_info *info)
 
 	if (info->attrs[NL802154_ATTR_IFTYPE]) {
 		type = nla_get_u32(info->attrs[NL802154_ATTR_IFTYPE]);
-		if (type > NL802154_IFTYPE_MAX ||
+		if (type > NL802154_IFTYPE_MAX || type < 0 ||
 		    !(rdev->wpan_phy.supported.iftypes & BIT(type)))
 			return -EINVAL;
 	}
-- 
2.30.2

Re: [PATCH] net: fix shift-out-of-bounds in nl802154_new_interface

[Alexander Aring]

Hi,

On Mon, 5 Apr 2021 at 15:58, Pavel Skripkin <paskripkin@gmail.com> wrote:
>
> syzbot reported shift-out-of-bounds in nl802154_new_interface.
> The problem was in signed representation of enum nl802154_iftype
>
> enum nl802154_iftype {
>         /* for backwards compatibility TODO */
>         NL802154_IFTYPE_UNSPEC = -1,
> ...
>
> Since, enum has negative value in it, objects of this type
> will be represented as signed integer.
>
>         type = nla_get_u32(info->attrs[NL802154_ATTR_IFTYPE]);
>
> u32 will be casted to signed, which can cause negative value type.
>
> Reported-by: syzbot+7bf7b22759195c9a21e9@syzkaller.appspotmail.com
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>

Yes, this patch will fix the issue but we discussed that the problem
is deeper than such a fix. The real problem is that we are using a -1
value which doesn't fit into the u32 netlink value and it gets
converted back and forward which we should avoid.

- Alex

Re: [PATCH] net: fix shift-out-of-bounds in nl802154_new_interface

[Pavel Skripkin]

On Tue, 2021-04-06 at 08:21 -0400, Alexander Aring wrote:
> Hi,
> 
> On Mon, 5 Apr 2021 at 15:58, Pavel Skripkin <paskripkin@gmail.com>
> wrote:
> > 
> > syzbot reported shift-out-of-bounds in nl802154_new_interface.
> > The problem was in signed representation of enum nl802154_iftype
> > 
> > enum nl802154_iftype {
> >         /* for backwards compatibility TODO */
> >         NL802154_IFTYPE_UNSPEC = -1,
> > ...
> > 
> > Since, enum has negative value in it, objects of this type
> > will be represented as signed integer.
> > 
> >         type = nla_get_u32(info->attrs[NL802154_ATTR_IFTYPE]);
> > 
> > u32 will be casted to signed, which can cause negative value type.
> > 
> > Reported-by: syzbot+7bf7b22759195c9a21e9@syzkaller.appspotmail.com
> > Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
> 
> Yes, this patch will fix the issue but we discussed that the problem
> is deeper than such a fix. The real problem is that we are using a -1
> value which doesn't fit into the u32 netlink value and it gets
> converted back and forward which we should avoid.
> 

OK, thanks for feedback!

> 
> - Alex

With regards,
Pavel Skripkin