Re: [PATCH v4 3/3] tests/qtest/fdc-test: Add a regression test for CVE-2021-20196

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

On 11/25/21 12:57, Hanna Reitz wrote:
> On 24.11.21 17:15, Philippe Mathieu-Daudé wrote:
>> 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.
>>
>> Suggested-by: Alexander Bulekov <alxndr@bu.edu>
>> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>>   tests/qtest/fdc-test.c | 38 ++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 38 insertions(+)
>>
>> diff --git a/tests/qtest/fdc-test.c b/tests/qtest/fdc-test.c
>> index 26b69f7c5cd..8f6eee84a47 100644
>> --- a/tests/qtest/fdc-test.c
>> +++ b/tests/qtest/fdc-test.c
>> @@ -32,6 +32,9 @@
>>   /* TODO actually test the results and get rid of this */
>>   #define qmp_discard_response(...) qobject_unref(qmp(__VA_ARGS__))
>>   +#define DRIVE_FLOPPY_BLANK \
>> +    "-drive
>> if=floppy,file=null-co://,file.read-zeroes=on,format=raw,size=1440k"
>> +
>>   #define TEST_IMAGE_SIZE 1440 * 1024
>>     #define FLOPPY_BASE 0x3f0
>> @@ -546,6 +549,40 @@ static void fuzz_registers(void)
>>       }
>>   }
>>   +static bool qtest_check_clang_sanitizer(void)
>> +{
>> +#if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
>> +    return true;
>> +#else
>> +    g_test_skip("QEMU not configured using --enable-sanitizers");
>> +    return false;
>> +#endif
>> +}
>> +static void test_cve_2021_20196(void)
>> +{
>> +    QTestState *s;
>> +
>> +    if (!qtest_check_clang_sanitizer()) {
>> +        return;
>> +    }
>> +
>> +    s = qtest_initf("-nographic -m 32M -nodefaults "
>> DRIVE_FLOPPY_BLANK);
>> +
>> +    qtest_outw(s, 0x3f4, 0x0500);
>> +    qtest_outb(s, 0x3f5, 0x00);
>> +    qtest_outb(s, 0x3f5, 0x00);
>> +    qtest_outw(s, 0x3f4, 0x0000);
>> +    qtest_outb(s, 0x3f5, 0x00);
>> +    qtest_outw(s, 0x3f1, 0x0400);
>> +    qtest_outw(s, 0x3f4, 0x0000);
>> +    qtest_outw(s, 0x3f4, 0x0000);
>> +    qtest_outb(s, 0x3f5, 0x00);
>> +    qtest_outb(s, 0x3f5, 0x01);
>> +    qtest_outw(s, 0x3f1, 0x0500);
>> +    qtest_outb(s, 0x3f5, 0x00);
>> +    qtest_quit(s);
>> +}
>> +
> 
> Now this works as a reproducer for me, but... this is a completely
> different I/O sequence now, right?

The patch Alexander sent [*] was indeed not working, but I could
manually reproduce, then I figure while the commit *description*
was working, the patch *content* was not accurate. This patch uses
the commit description.

[1] https://www.mail-archive.com/qemu-block@nongnu.org/msg82825.html

> Can’t complain, though, I didn’t understand the previous one, I can’t
> claim I need to understand this one or why they’re different.

Same here =)

> All the rest looks good to me, so all in all:
> 
> Reviewed-by: Hanna Reitz <hreitz@redhat.com>

Thank you!