Re: Assertion failure through vring_split_desc_read

[John Snow <jsnow@redhat.com>]

On 5/14/20 9:50 AM, Alexander Bulekov wrote:
> On 200514 1012, Philippe Mathieu-Daudé wrote:
>> On 5/14/20 1:24 AM, John Snow wrote:
>>>
>>>
>>> On 5/10/20 11:51 PM, Alexander Bulekov wrote:
>>>> 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: <20200511033001.dzvtbdhl3oz5pgiy@mozz.bu.edu>
>>>> 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
>>>>
>>>
>>> Do you have a writeup somewhere of how you are approaching fuzzing and
>>> how you've found this pile of bugs so far?
>>
>> There is docs/devel/fuzzing.txt:
>>
>> https://git.qemu.org/?p=qemu.git;a=blob;f=docs/devel/fuzzing.txt;hb=v5.0.0
>>
>>>
>>> Might make for a good blog post.
> 
> I am working on a patchset for the particular fuzzer I used to find
> these bugs. With that, I'll also update docs/devel/fuzzing.txt.
> 
>>
>> Good idea!
> 
> Yes I agree :)
> 

Awesome, I look forward to it. Thanks for the reports and the bugs filed
on LP.

--js