Date: Thu, 4 Apr 2024 08:26:09 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Cong Wang <xiyou.wangcong@...il.com>, 
	Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net] net/sched: act_skbmod: prevent kernel-infoleak

On Wed, Apr 3, 2024 at 9:09 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> syzbot found that tcf_skbmod_dump() was copying four bytes
> from kernel stack to user space [1].
>
> The issue here is that 'struct tc_skbmod' has a four bytes hole.
>
> We need to clear the structure before filling fields.
>
> [1]
> BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
>  BUG: KMSAN: kernel-infoleak in copy_to_user_iter lib/iov_iter.c:24 [inline]
>  BUG: KMSAN: kernel-infoleak in iterate_ubuf include/linux/iov_iter.h:29 [inline]
>  BUG: KMSAN: kernel-infoleak in iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
>  BUG: KMSAN: kernel-infoleak in iterate_and_advance include/linux/iov_iter.h:271 [inline]
>  BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x366/0x2520 lib/iov_iter.c:185
>   instrument_copy_to_user include/linux/instrumented.h:114 [inline]
>   copy_to_user_iter lib/iov_iter.c:24 [inline]
>   iterate_ubuf include/linux/iov_iter.h:29 [inline]
>   iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
>   iterate_and_advance include/linux/iov_iter.h:271 [inline]
>   _copy_to_iter+0x366/0x2520 lib/iov_iter.c:185
>   copy_to_iter include/linux/uio.h:196 [inline]
>   simple_copy_to_iter net/core/datagram.c:532 [inline]
>   __skb_datagram_iter+0x185/0x1000 net/core/datagram.c:420
>   skb_copy_datagram_iter+0x5c/0x200 net/core/datagram.c:546
>   skb_copy_datagram_msg include/linux/skbuff.h:4050 [inline]
>   netlink_recvmsg+0x432/0x1610 net/netlink/af_netlink.c:1962
>   sock_recvmsg_nosec net/socket.c:1046 [inline]
>   sock_recvmsg+0x2c4/0x340 net/socket.c:1068
>   __sys_recvfrom+0x35a/0x5f0 net/socket.c:2242
>   __do_sys_recvfrom net/socket.c:2260 [inline]
>   __se_sys_recvfrom net/socket.c:2256 [inline]
>   __x64_sys_recvfrom+0x126/0x1d0 net/socket.c:2256
>  do_syscall_64+0xd5/0x1f0
>  entry_SYSCALL_64_after_hwframe+0x6d/0x75
>
> Uninit was stored to memory at:
>   pskb_expand_head+0x30f/0x19d0 net/core/skbuff.c:2253
>   netlink_trim+0x2c2/0x330 net/netlink/af_netlink.c:1317
>   netlink_unicast+0x9f/0x1260 net/netlink/af_netlink.c:1351
>   nlmsg_unicast include/net/netlink.h:1144 [inline]
>   nlmsg_notify+0x21d/0x2f0 net/netlink/af_netlink.c:2610
>   rtnetlink_send+0x73/0x90 net/core/rtnetlink.c:741
>   rtnetlink_maybe_send include/linux/rtnetlink.h:17 [inline]
>   tcf_add_notify net/sched/act_api.c:2048 [inline]
>   tcf_action_add net/sched/act_api.c:2071 [inline]
>   tc_ctl_action+0x146e/0x19d0 net/sched/act_api.c:2119
>   rtnetlink_rcv_msg+0x1737/0x1900 net/core/rtnetlink.c:6595
>   netlink_rcv_skb+0x375/0x650 net/netlink/af_netlink.c:2559
>   rtnetlink_rcv+0x34/0x40 net/core/rtnetlink.c:6613
>   netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
>   netlink_unicast+0xf4c/0x1260 net/netlink/af_netlink.c:1361
>   netlink_sendmsg+0x10df/0x11f0 net/netlink/af_netlink.c:1905
>   sock_sendmsg_nosec net/socket.c:730 [inline]
>   __sock_sendmsg+0x30f/0x380 net/socket.c:745
>   ____sys_sendmsg+0x877/0xb60 net/socket.c:2584
>   ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
>   __sys_sendmsg net/socket.c:2667 [inline]
>   __do_sys_sendmsg net/socket.c:2676 [inline]
>   __se_sys_sendmsg net/socket.c:2674 [inline]
>   __x64_sys_sendmsg+0x307/0x4a0 net/socket.c:2674
>  do_syscall_64+0xd5/0x1f0
>  entry_SYSCALL_64_after_hwframe+0x6d/0x75
>
> Uninit was stored to memory at:
>   __nla_put lib/nlattr.c:1041 [inline]
>   nla_put+0x1c6/0x230 lib/nlattr.c:1099
>   tcf_skbmod_dump+0x23f/0xc20 net/sched/act_skbmod.c:256
>   tcf_action_dump_old net/sched/act_api.c:1191 [inline]
>   tcf_action_dump_1+0x85e/0x970 net/sched/act_api.c:1227
>   tcf_action_dump+0x1fd/0x460 net/sched/act_api.c:1251
>   tca_get_fill+0x519/0x7a0 net/sched/act_api.c:1628
>   tcf_add_notify_msg net/sched/act_api.c:2023 [inline]
>   tcf_add_notify net/sched/act_api.c:2042 [inline]
>   tcf_action_add net/sched/act_api.c:2071 [inline]
>   tc_ctl_action+0x1365/0x19d0 net/sched/act_api.c:2119
>   rtnetlink_rcv_msg+0x1737/0x1900 net/core/rtnetlink.c:6595
>   netlink_rcv_skb+0x375/0x650 net/netlink/af_netlink.c:2559
>   rtnetlink_rcv+0x34/0x40 net/core/rtnetlink.c:6613
>   netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
>   netlink_unicast+0xf4c/0x1260 net/netlink/af_netlink.c:1361
>   netlink_sendmsg+0x10df/0x11f0 net/netlink/af_netlink.c:1905
>   sock_sendmsg_nosec net/socket.c:730 [inline]
>   __sock_sendmsg+0x30f/0x380 net/socket.c:745
>   ____sys_sendmsg+0x877/0xb60 net/socket.c:2584
>   ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
>   __sys_sendmsg net/socket.c:2667 [inline]
>   __do_sys_sendmsg net/socket.c:2676 [inline]
>   __se_sys_sendmsg net/socket.c:2674 [inline]
>   __x64_sys_sendmsg+0x307/0x4a0 net/socket.c:2674
>  do_syscall_64+0xd5/0x1f0
>  entry_SYSCALL_64_after_hwframe+0x6d/0x75
>
> Local variable opt created at:
>   tcf_skbmod_dump+0x9d/0xc20 net/sched/act_skbmod.c:244
>   tcf_action_dump_old net/sched/act_api.c:1191 [inline]
>   tcf_action_dump_1+0x85e/0x970 net/sched/act_api.c:1227
>
> Bytes 188-191 of 248 are uninitialized
> Memory access of size 248 starts at ffff888117697680
> Data copied to user address 00007ffe56d855f0
>
> Fixes: 86da71b57383 ("net_sched: Introduce skbmod action")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal

> ---
>  net/sched/act_skbmod.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/net/sched/act_skbmod.c b/net/sched/act_skbmod.c
> index 39945b139c4817584fb9803b9e65c89fef68eca0..cd0accaf844a18e4a6a626adba5fae05df66b0a3 100644
> --- a/net/sched/act_skbmod.c
> +++ b/net/sched/act_skbmod.c
> @@ -241,13 +241,13 @@ static int tcf_skbmod_dump(struct sk_buff *skb, struct tc_action *a,
>         struct tcf_skbmod *d = to_skbmod(a);
>         unsigned char *b = skb_tail_pointer(skb);
>         struct tcf_skbmod_params  *p;
> -       struct tc_skbmod opt = {
> -               .index   = d->tcf_index,
> -               .refcnt  = refcount_read(&d->tcf_refcnt) - ref,
> -               .bindcnt = atomic_read(&d->tcf_bindcnt) - bind,
> -       };
> +       struct tc_skbmod opt;
>         struct tcf_t t;
>
> +       memset(&opt, 0, sizeof(opt));
> +       opt.index   = d->tcf_index;
> +       opt.refcnt  = refcount_read(&d->tcf_refcnt) - ref,
> +       opt.bindcnt = atomic_read(&d->tcf_bindcnt) - bind;
>         spin_lock_bh(&d->tcf_lock);
>         opt.action = d->tcf_action;
>         p = rcu_dereference_protected(d->skbmod_p,
> --
> 2.44.0.478.gd926399ef9-goog
>

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