Commit 8aa34834 authored by Alberto Garcia's avatar Alberto Garcia Committed by Max Reitz
Browse files

qcow2: Prevent allocating compressed clusters at offset 0 



If the refcount data is corrupted then we can end up trying to
allocate a new compressed cluster at offset 0 in the image, triggering
an assertion in qcow2_alloc_bytes() that would crash QEMU:

  qcow2_alloc_bytes: Assertion `offset' failed.

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

Signed-off-by: default avatarAlberto Garcia <berto@igalia.com>
Message-id: fb53467cf48e95ff3330def1cf1003a5b862b7d9.1509718618.git.berto@igalia.com
Reviewed-by: default avatarMax Reitz <mreitz@redhat.com>
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
parent 98839750

block/qcow2-refcount.c

+7 −0
Original line number Diff line number Diff line
@@ -1082,6 +1082,13 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size) 
                return new_cluster;

            }



            if (new_cluster == 0) {

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

                                        "allocation of compressed cluster "

                                        "at offset 0");

                return -EIO;

            }



            if (!offset || ROUND_UP(offset, s->cluster_size) != new_cluster) {

                offset = new_cluster;

                free_in_cluster = s->cluster_size;

tests/qemu-iotests/060

+10 −0
Original line number Diff line number Diff line
@@ -260,6 +260,16 @@ _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



echo

echo "=== Testing empty refcount block with compressed write ==="

echo

_make_test_img 64M

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

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

# The previous write already allocated an L2 table, so now this new

# write will try to allocate a compressed data cluster at offset 0.

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



# success, all done

echo "*** done"

rm -f $seq.full

tests/qemu-iotests/060.out

+8 −0
Original line number Diff line number Diff line
@@ -195,4 +195,12 @@ write failed: Input/output error 
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



=== Testing empty refcount block with compressed write ===



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

wrote 65536/65536 bytes at offset 65536

64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)

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

write failed: Input/output error

*** done