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

[Hanna Reitz]

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]?

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.

Hanna