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From:   Vishnu Dasa <vdasa@vmware.com>
To:     Alexander Potapenko <glider@google.com>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "georgezhang@vmware.com" <georgezhang@vmware.com>,
        Bryan Tan <bryantan@vmware.com>,
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        "syzbot+39be4da489ed2493ba25@syzkaller.appspotmail.com" 
        <syzbot+39be4da489ed2493ba25@syzkaller.appspotmail.com>
Subject: Re: [PATCH] misc/vmw_vmci: fix an infoleak in
 vmci_host_do_receive_datagram()
Thread-Topic: [PATCH] misc/vmw_vmci: fix an infoleak in
 vmci_host_do_receive_datagram()
Thread-Index: AQHY8HccmPEqSy5Tt0iqpaQK6n1bVa4z4mKA
Date:   Mon, 7 Nov 2022 19:46:42 +0000
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> On Nov 4, 2022, at 10:58 AM, Alexander Potapenko <glider@google.com> wrot=
e:
>=20
> `struct vmci_event_qp` allocated by qp_notify_peer() contains padding,
> which may carry uninitialized data to the userspace, as observed by
> KMSAN:
>=20
>  BUG: KMSAN: kernel-infoleak in instrument_copy_to_user ./include/linux/i=
nstrumented.h:121
>   instrument_copy_to_user ./include/linux/instrumented.h:121
>   _copy_to_user+0x5f/0xb0 lib/usercopy.c:33
>   copy_to_user ./include/linux/uaccess.h:169
>   vmci_host_do_receive_datagram drivers/misc/vmw_vmci/vmci_host.c:431
>   vmci_host_unlocked_ioctl+0x33d/0x43d0 drivers/misc/vmw_vmci/vmci_host.c=
:925
>   vfs_ioctl fs/ioctl.c:51
>  ...
>=20
>  Uninit was stored to memory at:
>   kmemdup+0x74/0xb0 mm/util.c:131
>   dg_dispatch_as_host drivers/misc/vmw_vmci/vmci_datagram.c:271
>   vmci_datagram_dispatch+0x4f8/0xfc0 drivers/misc/vmw_vmci/vmci_datagram.=
c:339
>   qp_notify_peer+0x19a/0x290 drivers/misc/vmw_vmci/vmci_queue_pair.c:1479
>   qp_broker_attach drivers/misc/vmw_vmci/vmci_queue_pair.c:1662
>   qp_broker_alloc+0x2977/0x2f30 drivers/misc/vmw_vmci/vmci_queue_pair.c:1=
750
>   vmci_qp_broker_alloc+0x96/0xd0 drivers/misc/vmw_vmci/vmci_queue_pair.c:=
1940
>   vmci_host_do_alloc_queuepair drivers/misc/vmw_vmci/vmci_host.c:488
>   vmci_host_unlocked_ioctl+0x24fd/0x43d0 drivers/misc/vmw_vmci/vmci_host.=
c:927
>  ...
>=20
>  Local variable ev created at:
>   qp_notify_peer+0x54/0x290 drivers/misc/vmw_vmci/vmci_queue_pair.c:1456
>   qp_broker_attach drivers/misc/vmw_vmci/vmci_queue_pair.c:1662
>   qp_broker_alloc+0x2977/0x2f30 drivers/misc/vmw_vmci/vmci_queue_pair.c:1=
750
>=20
>  Bytes 28-31 of 48 are uninitialized
>  Memory access of size 48 starts at ffff888035155e00
>  Data copied to user address 0000000020000100
>=20
> Use memset() to prevent the infoleaks.
>=20
> Also speculatively fix qp_notify_peer_local(), which may suffer from the
> same problem.
>=20

Thanks for the fix!

Regards,
Vishnu

> Reported-by: syzbot+39be4da489ed2493ba25@syzkaller.appspotmail.com
> Fixes: 06164d2b72aa ("VMCI: queue pairs implementation.")
> Signed-off-by: Alexander Potapenko <glider@google.com>

Reviewed-by: Vishnu Dasa <vdasa@vmware.com>

> ---
> drivers/misc/vmw_vmci/vmci_queue_pair.c | 2 ++
> 1 file changed, 2 insertions(+)
>=20
> diff --git a/drivers/misc/vmw_vmci/vmci_queue_pair.c b/drivers/misc/vmw_v=
mci/vmci_queue_pair.c
> index e71068f7759b3..844264e1b88cc 100644
> --- a/drivers/misc/vmw_vmci/vmci_queue_pair.c
> +++ b/drivers/misc/vmw_vmci/vmci_queue_pair.c
> @@ -854,6 +854,7 @@ static int qp_notify_peer_local(bool attach, struct v=
mci_handle handle)
> 	u32 context_id =3D vmci_get_context_id();
> 	struct vmci_event_qp ev;
>=20
> +	memset(&ev, 0, sizeof(ev));
> 	ev.msg.hdr.dst =3D vmci_make_handle(context_id, VMCI_EVENT_HANDLER);
> 	ev.msg.hdr.src =3D vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
> 					  VMCI_CONTEXT_RESOURCE_ID);
> @@ -1467,6 +1468,7 @@ static int qp_notify_peer(bool attach,
> 	 * kernel.
> 	 */
>=20
> +	memset(&ev, 0, sizeof(ev));
> 	ev.msg.hdr.dst =3D vmci_make_handle(peer_id, VMCI_EVENT_HANDLER);
> 	ev.msg.hdr.src =3D vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
> 					  VMCI_CONTEXT_RESOURCE_ID);
> --=20
> 2.38.1.431.g37b22c650d-goog
>=20