vhost: crash in vhost_user_tx_avx2

(gdb) bt
bt
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
(gdb) frame 5
frame 5
293	      if (PREDICT_FALSE (rxvq->last_avail_idx == rxvq->avail->idx))
(gdb) p *rxvq
p *rxvq
$3 = {cacheline0 = 0x7f290bcadd80 "\377\003", qsz_mask = 1023, last_avail_idx = 0, last_used_idx = 0, n_since_last_int = 0, desc = 0x0, avail = 0x0, used = 0x0, int_deadline = 0, started = 1 '\001', enabled = 1 '\001', log_used = 0 '\000', cacheline1 = 0x7f290bcaddc0 "\377\377\377\377\016", errfd = -1, callfd_idx = 14, kickfd_idx = 19, log_guest_addr = 5151049792, mode = 0}

The crash is because we access the null pointer rxvq->avail,
which is supposed to be derived from the mmap informed by the driver.
We fixed a similar issue before in

    https://gerrit.fd.io/r/#/c/14545/

The reason was the driver ummaps the memory without doing the disconnect in
SR-IOV environment. The fixed was applied to the RX path. Now it happens in the
TX path. We just need to apply the same check in the TX path.

Change-Id: I7b1dfc96797cb5b52845bc6cec09a8c5d4325280
Signed-off-by: Steven <sluong@cisco.com>

diff --git a/src/vnet/devices/virtio/vhost_user_output.c b/src/vnet/devices/virtio/vhost_user_output.c
index 8205949..9b6c017 100644 (file)
--- a/src/vnet/devices/virtio/vhost_user_output.c
+++ b/src/vnet/devices/virtio/vhost_user_output.c
@@ -261,6 +261,12 @@ VNET_DEVICE_CLASS_TX_FN (vhost_user_device_class) (vlib_main_t * vm,
     VHOST_VRING_IDX_RX (*vec_elt_at_index
                        (vui->per_cpu_tx_qid, thread_index));
   rxvq = &vui->vrings[qid];
+  if (PREDICT_FALSE (rxvq->avail == 0))
+    {
+      error = VHOST_USER_TX_FUNC_ERROR_MMAP_FAIL;
+      goto done3;
+    }
+
   if (PREDICT_FALSE (vui->use_tx_spinlock))
     vhost_user_vring_lock (vui, qid);