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

From: Hanna Reitz
Subject: Re: [PATCH-for-6.2 v3 2/2] tests/qtest/fdc-test: Add a regression test for CVE-2021-20196
Date: Tue, 23 Nov 2021 14:42:10 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0

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:

   ==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.


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