Re: [PATCH-for-6.2 v3 2/2] tests/qtest/fdc-test: Add a regression test for CVE-2021-20196

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 11/23/21 14:42, Hanna Reitz wrote:
> On 18.11.21 13:06, Philippe Mathieu-Daudé wrote:
>> From: Alexander Bulekov <alxndr@bu.edu>
>>
>> Without the previous commit, when running 'make check-qtest-i386'
>> with QEMU configured with '--enable-sanitizers' we get:
>>
>>    AddressSanitizer:DEADLYSIGNAL
>>    =================================================================
>>    ==287878==ERROR: AddressSanitizer: SEGV on unknown address
>> 0x000000000344
>>    ==287878==The signal is caused by a WRITE memory access.
>>    ==287878==Hint: address points to the zero page.
>>        #0 0x564b2e5bac27 in blk_inc_in_flight
>> block/block-backend.c:1346:5
>>        #1 0x564b2e5bb228 in blk_pwritev_part block/block-backend.c:1317:5
>>        #2 0x564b2e5bcd57 in blk_pwrite block/block-backend.c:1498:11
>>        #3 0x564b2ca1cdd3 in fdctrl_write_data hw/block/fdc.c:2221:17
>>        #4 0x564b2ca1b2f7 in fdctrl_write hw/block/fdc.c:829:9
>>        #5 0x564b2dc49503 in portio_write softmmu/ioport.c:201:9
>>
>> Add the reproducer for CVE-2021-20196.
>>
>> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
>> Message-Id: <20210319050906.14875-2-alxndr@bu.edu>
>> [PMD: Rebased, use global test_image]
>> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>>   tests/qtest/fdc-test.c | 21 +++++++++++++++++++++
>>   1 file changed, 21 insertions(+)
> 
> Not sure if I’m doing something wrong, but:
> 
> Using the global test_image brings a problem, namely that this test
> fails unconditionally (for me at least...?), with the reason being that
> the global QEMU instance (launched by qtest_start(), quit by
> qtest_end()) still has that image open, so by launching a second
> instance concurrently, I get this:
> 
> qemu-system-x86_64: Failed to get "write" lock
> Is another process using the image [/tmp/qtest.xV4IxX]?

Hmm I had too many odd problems running qtests in parallel so I
switched to 'make check-qtest -j1' more than 1 year ago, which
is probably why I haven't noticed that issue.

Using another 'test_image' seems against code reuse principle,
but at this point in release, duplicating it is simpler. Someone
will clean that later =)

> So either we need to use a different image file, or we need to quit the
> global instance before using it (e.g. putting a qtest_end() at the
> beginning of test_cve_*()), although the latter just seems wrong.
> 
> Second, I can’t make this test fail.  When I apply this patch first (to
> master) and run it, I don’t get a SIGSEGV.

Is your QEMU built with --enable-sanitizers ?