Linux Virtualization - Dec 2019 - [PATCH net 0/2] vsock/virtio: fix null-pointer dereference and related precautions

This series mainly solves a possible null-pointer dereference in
virtio_transport_recv_listen() introduced with the multi-transport
support [PATCH 1].

PATCH 2 adds a WARN_ON check for the same potential issue
and a returned error in the virtio_transport_send_pkt_info() function
to avoid crashing the kernel.

Stefano Garzarella (2):
  vsock/virtio: fix null-pointer dereference in
    virtio_transport_recv_listen()
  vsock/virtio: add WARN_ON check on virtio_transport_get_ops()

 net/vmw_vsock/virtio_transport_common.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

-- 
2.23.0

With multi-transport support, listener sockets are not bound to any
transport. So, calling virtio_transport_reset(), when an error
occurs, on a listener socket produces the following null-pointer
dereference:

  BUG: kernel NULL pointer dereference, address: 00000000000000e8
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] SMP PTI
  CPU: 0 PID: 20 Comm: kworker/0:1 Not tainted
5.5.0-rc1-ste-00003-gb4be21f316ac-dirty #56
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
  Workqueue: virtio_vsock virtio_transport_rx_work [vmw_vsock_virtio_transport]
  RIP: 0010:virtio_transport_send_pkt_info+0x20/0x130
[vmw_vsock_virtio_transport_common]
  Code: 1f 84 00 00 00 00 00 0f 1f 00 55 48 89 e5 41 57 41 56 41 55 49 89 f5 41
54 49 89 fc 53 48 83 ec 10 44 8b 76 20 e8 c0 ba fe ff <48> 8b 80 e8 00 00
00 e8 64 e3 7d c1 45 8b 45 00 41 8b 8c 24 d4 02
  RSP: 0018:ffffc900000b7d08 EFLAGS: 00010282
  RAX: 0000000000000000 RBX: ffff88807bf12728 RCX: 0000000000000000
  RDX: ffff88807bf12700 RSI: ffffc900000b7d50 RDI: ffff888035c84000
  RBP: ffffc900000b7d40 R08: ffff888035c84000 R09: ffffc900000b7d08
  R10: ffff8880781de800 R11: 0000000000000018 R12: ffff888035c84000
  R13: ffffc900000b7d50 R14: 0000000000000000 R15: ffff88807bf12724
  FS:  0000000000000000(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00000000000000e8 CR3: 00000000790f4004 CR4: 0000000000160ef0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   virtio_transport_reset+0x59/0x70 [vmw_vsock_virtio_transport_common]
   virtio_transport_recv_pkt+0x5bb/0xe50 [vmw_vsock_virtio_transport_common]
   ? detach_buf_split+0xf1/0x130
   virtio_transport_rx_work+0xba/0x130 [vmw_vsock_virtio_transport]
   process_one_work+0x1c0/0x300
   worker_thread+0x45/0x3c0
   kthread+0xfc/0x130
   ? current_work+0x40/0x40
   ? kthread_park+0x90/0x90
   ret_from_fork+0x35/0x40
  Modules linked in: sunrpc kvm_intel kvm vmw_vsock_virtio_transport
vmw_vsock_virtio_transport_common irqbypass vsock virtio_rng rng_core
  CR2: 00000000000000e8
  ---[ end trace e75400e2ea2fa824 ]---

This happens because virtio_transport_reset() calls
virtio_transport_send_pkt_info() that can be used only on
connecting/connected sockets.

This patch fixes the issue, using virtio_transport_reset_no_sock()
instead of virtio_transport_reset() when we are handling a listener
socket.

Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
---
 net/vmw_vsock/virtio_transport_common.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c
b/net/vmw_vsock/virtio_transport_common.c
index e5ea29c6bca7..f5991006190e 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -1021,18 +1021,18 @@ virtio_transport_recv_listen(struct sock *sk, struct
virtio_vsock_pkt *pkt,
 	int ret;
 
 	if (le16_to_cpu(pkt->hdr.op) != VIRTIO_VSOCK_OP_REQUEST) {
-		virtio_transport_reset(vsk, pkt);
+		virtio_transport_reset_no_sock(t, pkt);
 		return -EINVAL;
 	}
 
 	if (sk_acceptq_is_full(sk)) {
-		virtio_transport_reset(vsk, pkt);
+		virtio_transport_reset_no_sock(t, pkt);
 		return -ENOMEM;
 	}
 
 	child = vsock_create_connected(sk);
 	if (!child) {
-		virtio_transport_reset(vsk, pkt);
+		virtio_transport_reset_no_sock(t, pkt);
 		return -ENOMEM;
 	}
 
@@ -1054,7 +1054,7 @@ virtio_transport_recv_listen(struct sock *sk, struct
virtio_vsock_pkt *pkt,
 	 */
 	if (ret || vchild->transport != &t->transport) {
 		release_sock(child);
-		virtio_transport_reset(vsk, pkt);
+		virtio_transport_reset_no_sock(t, pkt);
 		sock_put(child);
 		return ret;
 	}
-- 
2.23.0

virtio_transport_get_ops() and virtio_transport_send_pkt_info()
can only be used on connecting/connected sockets, since a socket
assigned to a transport is required.

This patch adds a WARN_ON() on virtio_transport_get_ops() to check
this requirement, a comment and a returned error on
virtio_transport_send_pkt_info(),

Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
---
 net/vmw_vsock/virtio_transport_common.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c
b/net/vmw_vsock/virtio_transport_common.c
index f5991006190e..6abec3fc81d1 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -34,6 +34,9 @@ virtio_transport_get_ops(struct vsock_sock *vsk)
 {
 	const struct vsock_transport *t = vsock_core_get_transport(vsk);
 
+	if (WARN_ON(!t))
+		return NULL;
+
 	return container_of(t, struct virtio_transport, transport);
 }
 
@@ -161,15 +164,25 @@ void virtio_transport_deliver_tap_pkt(struct
virtio_vsock_pkt *pkt)
 }
 EXPORT_SYMBOL_GPL(virtio_transport_deliver_tap_pkt);
 
+/* This function can only be used on connecting/connected sockets,
+ * since a socket assigned to a transport is required.
+ *
+ * Do not use on listener sockets!
+ */
 static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 					  struct virtio_vsock_pkt_info *info)
 {
 	u32 src_cid, src_port, dst_cid, dst_port;
+	const struct virtio_transport *t_ops;
 	struct virtio_vsock_sock *vvs;
 	struct virtio_vsock_pkt *pkt;
 	u32 pkt_len = info->pkt_len;
 
-	src_cid = virtio_transport_get_ops(vsk)->transport.get_local_cid();
+	t_ops = virtio_transport_get_ops(vsk);
+	if (unlikely(!t_ops))
+		return -EFAULT;
+
+	src_cid = t_ops->transport.get_local_cid();
 	src_port = vsk->local_addr.svm_port;
 	if (!info->remote_cid) {
 		dst_cid	= vsk->remote_addr.svm_cid;
@@ -202,7 +215,7 @@ static int virtio_transport_send_pkt_info(struct vsock_sock
*vsk,
 
 	virtio_transport_inc_tx_pkt(vvs, pkt);
 
-	return virtio_transport_get_ops(vsk)->send_pkt(pkt);
+	return t_ops->send_pkt(pkt);
 }
 
 static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
-- 
2.23.0

From: Stefano Garzarella <sgarzare at redhat.com>
Date: Fri, 13 Dec 2019 19:47:59 +0100
> This series mainly solves a possible null-pointer dereference in
> virtio_transport_recv_listen() introduced with the multi-transport
> support [PATCH 1].
> 
> PATCH 2 adds a WARN_ON check for the same potential issue
> and a returned error in the virtio_transport_send_pkt_info() function
> to avoid crashing the kernel.
Series applied, thanks.