Assertion failure through vring_split_desc_read

[Alexander Bulekov]

Hello,
While fuzzing, I found an input that triggers an assertion failure
through virtio-rng -> vring_split_desc_read. Maybe this is related to:
Message-ID: <address@hidden> 
Assertion failure through virtio_lduw_phys_cached

#8 0x7fe6a9acf091 in __assert_fail 
/build/glibc-GwnBeO/glibc-2.30/assert/assert.c:101:3
#9 0x564cbe7d96fd in address_space_read_cached include/exec/memory.h:2423:5
#10 0x564cbe7e79c5 in vring_split_desc_read hw/virtio/virtio.c:236:5
#11 0x564cbe7e84ce in virtqueue_split_read_next_desc hw/virtio/virtio.c:929:5
#12 0x564cbe78f86b in virtqueue_split_get_avail_bytes hw/virtio/virtio.c:1009:18
#13 0x564cbe78ab22 in virtqueue_get_avail_bytes hw/virtio/virtio.c:1208:9
#14 0x564cc08aade1 in get_request_size hw/virtio/virtio-rng.c:40:5
#15 0x564cc08aa20b in virtio_rng_process hw/virtio/virtio-rng.c:115:12
#16 0x564cc08a8c48 in virtio_rng_set_status hw/virtio/virtio-rng.c:172:5
#17 0x564cbe7a50be in virtio_set_status hw/virtio/virtio.c:1876:9
#18 0x564cc08d1b8f in virtio_pci_common_write hw/virtio/virtio-pci.c:1245:9

I can reproduce it in a qemu 5.0 build using these qtest commands:
https://paste.debian.net/plain/1146089
(not including them here, as some are quite long)

wget https://paste.debian.net/plain/1146089 -O qtest-trace; 
~/Development/qemu/build/i386-softmmu/qemu-system-i386 -M pc-q35-5.0  -device 
virtio-rng-pci,addr=04.0 -display none -nodefaults -nographic -qtest stdio < 
qtest-trace

Please let me know if I can provide any further info.
-Alex