Re: [PATCH RESEND] mac802154: Fix uninit-value access in ieee802154_hdr_push_sechdr

[Alexander Aring]

Hi,

On Sun, Jan 14, 2024 at 10:32 PM Alexander Aring <aahringo@xxxxxxxxxx> wrote:
>
> Hi,
>
> On Fri, Jan 12, 2024 at 8:16 AM Nikita Zhandarovich
> <n.zhandarovich@xxxxxxxxxx> wrote:
> >
> > >> > >
> > >> > > BUG: KMSAN: uninit-value in ieee802154_hdr_push_sechdr net/ieee802154=
> > > /header_ops.c:54 [inline]
> > >> > > BUG: KMSAN: uninit-value in ieee802154_hdr_push+0x971/0xb90 net/ieee8=
> > > 02154/header_ops.c:108
> > >> > >  ieee802154_hdr_push_sechdr net/ieee802154/header_ops.c:54 [inline]
> > >> > >  ieee802154_hdr_push+0x971/0xb90 net/ieee802154/header_ops.c:108
> > >> > >  ieee802154_header_create+0x9c0/0xc00 net/mac802154/iface.c:396
> > >> > >  wpan_dev_hard_header include/net/cfg802154.h:494 [inline]
> > >> > >  dgram_sendmsg+0xd1d/0x1500 net/ieee802154/socket.c:677
> > >> > >  ieee802154_sock_sendmsg+0x91/0xc0 net/ieee802154/socket.c:96
> > >> > >  sock_sendmsg_nosec net/socket.c:725 [inline]
> > >> > >  sock_sendmsg net/socket.c:748 [inline]
> > >> > >  ____sys_sendmsg+0x9c2/0xd60 net/socket.c:2494
> > >> > >  ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2548
> > >> > >  __sys_sendmsg+0x225/0x3c0 net/socket.c:2577
> > >> > >  __compat_sys_sendmsg net/compat.c:346 [inline]
> > >> > >  __do_compat_sys_sendmsg net/compat.c:353 [inline]
> > >> > >  __se_compat_sys_sendmsg net/compat.c:350 [inline]
> > >> > >
> > >> > > We found hdr->key_id_mode is uninitialized in mac802154_set_header_se=
> > > curity()
> > >> > > which indicates hdr.fc.security_enabled should be 0. However, it is s=
> > > et to be cb->secen before.
> > >> > > Later, ieee802154_hdr_push_sechdr is invoked, causing KMSAN complains=
> > >  uninit-value issue.
> > >> >
> > >> > I am not too deeply involved in the security header but for me it feels
> > >> > like your patch does the opposite of what's needed. We should maybe
> > >> > initialize hdr->key_id_mode based on the value in cb->secen, no? (maybe
> > >> > Alexander will have a better understanding than I have).
> > >>
> > >> I can't help yet with a better answer why syzkaller reports it but it
> > >> will break things as we using skb->cb to pass additional parameters
> > >> through header_ops->create()... in this case it is some sockopts of
> > >> af802154, I guess.
> > >>
> > >
> > > Maybe we just need to init some "more" defaults in [0]
> > >
> > > - Alex
> > >
> > > [0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree=
> > > /net/ieee802154/socket.c?h=3Dv6.7-rc5#n474
> >
> > Hello,
> >
> > I was looking into the same issue (now present in syzbot [1]) and since it has a
> > C-repro, the error is easy to recreate. Apparently, despite cb->secen (and
> > hdr.fc.security_enabled accordingly) being equal 1, mac802154_set_header_security()
> > finishes with 0 in:
> >
> >         if (!params.enabled ||
> >             (cb->secen_override && !cb->secen) ||
> >             !params.out_level)
> >             return 0;
> >
> > Not presuming to understand the issue fully but if we do end up leaving
> > mac802154_set_header_security() early, should we init hdr->key_id_mode
> > with IEEE802154_SCF_KEY_IMPLICIT before returning with 0?
> > I imagine that reseting hdr.fc.security_enabled to 0 ourselves in this
> > case is a wrong way to go too.
> >
>
> I think here are two problems:
>
> 1.
> When (in any way) secen path is hit then we should make sure some
> other security parameters are set, if not return with an error. This
> needs to be done somewhere in the 802.15.4 socket code. [0]
>

This would require that we init them with some invalid value defaults
but I think because we are using bit fields, we need to change the
whole struct to make some invalid number range available.
I am happy to init those values to some value at [0] to at least get
rid of the uninit value warning. We can change it so that it fails at
send() afterwards, I think it should fail in some later path of the
implementation that ends in a kernel log message.

- Alex

[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/ieee802154/socket.c#n474