Commit 98839750 authored by Alberto Garcia's avatar Alberto Garcia Committed by Max Reitz
Browse files

qcow2: Prevent allocating L2 tables at offset 0 



If the refcount data is corrupted then we can end up trying to
allocate a new L2 table at offset 0 in the image, triggering an
assertion in the qcow2 cache that would crash QEMU:

  qcow2_cache_entry_mark_dirty: Assertion `c->entries[i].offset != 0' failed

This patch adds an explicit check for this scenario and a new test
case.

Signed-off-by: default avatarAlberto Garcia <berto@igalia.com>
Reviewed-by: default avatarMax Reitz <mreitz@redhat.com>
Message-id: 92dac37191ae7844a2da22c122204eb493cc3133.1509718618.git.berto@igalia.com
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
parent 6bf45d59

block/qcow2-cluster.c

+8 −0
Original line number Diff line number Diff line
@@ -278,6 +278,14 @@ static int l2_allocate(BlockDriverState *bs, int l1_index, uint64_t **table) 
        goto fail;

    }



    /* If we're allocating the table at offset 0 then something is wrong */

    if (l2_offset == 0) {

        qcow2_signal_corruption(bs, true, -1, -1, "Preventing invalid "

                                "allocation of L2 table at offset 0");

        ret = -EIO;

        goto fail;

    }



    ret = qcow2_cache_flush(bs, s->refcount_block_cache);

    if (ret < 0) {

        goto fail;

tests/qemu-iotests/060

+7 −0
Original line number Diff line number Diff line
@@ -253,6 +253,13 @@ poke_file "$TEST_IMG" "$rt_offset" "\x00\x00\x00\x00\x00\x00\x00\x00" 
# causing a refcount block to be allocated at offset 0

$QEMU_IO -c "write 0 128k" "$TEST_IMG" | _filter_qemu_io



echo

echo "=== Testing empty refcount block ==="

echo

_make_test_img 64M

poke_file "$TEST_IMG" "$rb_offset"        "\x00\x00\x00\x00\x00\x00\x00\x00"

$QEMU_IO -c "write 0 64k" "$TEST_IMG" | _filter_qemu_io



# success, all done

echo "*** done"

rm -f $seq.full

tests/qemu-iotests/060.out

+6 −0
Original line number Diff line number Diff line
@@ -189,4 +189,10 @@ wrote 65536/65536 bytes at offset 0 
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)

qcow2: Marking image as corrupt: Preventing invalid allocation of refcount block at offset 0; further corruption events will be suppressed

write failed: Input/output error



=== Testing empty refcount block ===



Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864

qcow2: Marking image as corrupt: Preventing invalid allocation of L2 table at offset 0; further corruption events will be suppressed

write failed: Input/output error

*** done