[dpdk-stable] [17.11 LTS PATCH v2] vhost: fix vring requests validation broken if no FD

[Maxime Coquelin]

From: Zhike Wang <wangzk320 at 163.com>

When VHOST_USER_VRING_NOFD_MASK is set, the fd_num is 0,
so validate_msg_fds() will return error. In this case,
the negotiation of vring message between vhost user front end and
back end would fail, and as a result, vhost user link could NOT be up.

How to reproduce:
1.Run dpdk testpmd insides VM, which locates at host with ovs+dpdk.
2.Notice that inside ovs there are endless logs regarding failure to
handle VHOST_USER_SET_VRING_CALL, and link of vm could NOT be up.

Fixes: 1f6147d9a01f ("vhost: fix possible denial of service by leaking FDs")
Cc: stable at dpdk.org

Signed-off-by: Zhike Wang <wangzk320 at 163.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin at redhat.com>
---
 lib/librte_vhost/vhost_user.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index d4643dc350..155394a6d9 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -1409,6 +1409,7 @@ vhost_user_msg_handler(int vid, int fd)
 	struct VhostUserMsg msg;
 	int ret;
 	int unlock_required = 0;
+	int expected_fds;
 
 	dev = get_device(vid);
 	if (dev == NULL)
@@ -1586,20 +1587,26 @@ vhost_user_msg_handler(int vid, int fd)
 		break;
 
 	case VHOST_USER_SET_VRING_KICK:
-		if (validate_msg_fds(&msg, 1) != 0)
+		expected_fds =
+			(msg.payload.u64 & VHOST_USER_VRING_NOFD_MASK) ? 0 : 1;
+		if (validate_msg_fds(&msg, expected_fds) != 0)
 			return -1;
 
 		vhost_user_set_vring_kick(&dev, &msg);
 		break;
 	case VHOST_USER_SET_VRING_CALL:
-		if (validate_msg_fds(&msg, 1) != 0)
+		expected_fds =
+			(msg.payload.u64 & VHOST_USER_VRING_NOFD_MASK) ? 0 : 1;
+		if (validate_msg_fds(&msg, expected_fds) != 0)
 			return -1;
 
 		vhost_user_set_vring_call(dev, &msg);
 		break;
 
 	case VHOST_USER_SET_VRING_ERR:
-		if (validate_msg_fds(&msg, 1) != 0)
+		expected_fds =
+			(msg.payload.u64 & VHOST_USER_VRING_NOFD_MASK) ? 0 : 1;
+		if (validate_msg_fds(&msg, expected_fds) != 0)
 			return -1;
 
 		if (!(msg.payload.u64 & VHOST_USER_VRING_NOFD_MASK))
-- 
2.21.0