Commit a1b3955c authored by Kevin Wolf's avatar Kevin Wolf Committed by Stefan Hajnoczi
Browse files

qcow2: Check backing_file_offset (CVE-2014-0144) 



Header, header extension and the backing file name must all be stored in
the first cluster. Setting the backing file to a much higher value
allowed header extensions to become much bigger than we want them to be
(unbounded allocation).

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Reviewed-by: default avatarMax Reitz <mreitz@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 24342f2c

block/qcow2.c

+6 −0
Original line number Diff line number Diff line
@@ -511,6 +511,12 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags, 
        }

    }



    if (header.backing_file_offset > s->cluster_size) {

        error_setg(errp, "Invalid backing file offset");

        ret = -EINVAL;

        goto fail;

    }



    if (header.backing_file_offset) {

        ext_end = header.backing_file_offset;

    } else {

tests/qemu-iotests/080

+12 −0
Original line number Diff line number Diff line
@@ -43,6 +43,8 @@ _supported_proto generic 
_supported_os Linux



header_size=104



offset_backing_file_offset=8

offset_header_size=100

offset_ext_magic=$header_size

offset_ext_size=$((header_size + 4))
@@ -55,6 +57,16 @@ poke_file "$TEST_IMG" "$offset_header_size" "\xff\xff\xff\xff" 
poke_file "$TEST_IMG" "$offset_header_size" "\x7f\xff\xff\xff"

{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir



echo

echo "== Huge unknown header extension =="

_make_test_img 64M

poke_file "$TEST_IMG" "$offset_backing_file_offset" "\xff\xff\xff\xff\xff\xff\xff\xff"

poke_file "$TEST_IMG" "$offset_ext_magic" "\x12\x34\x56\x78"

poke_file "$TEST_IMG" "$offset_ext_size" "\x7f\xff\xff\xff"

{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir

poke_file "$TEST_IMG" "$offset_backing_file_offset" "\x00\x00\x00\x00\x00\x00\x00\x00"

{ $QEMU_IO -c "read 0 512" $TEST_IMG; } 2>&1 | _filter_qemu_io | _filter_testdir



# success, all done

echo "*** done"

rm -f $seq.full

tests/qemu-iotests/080.out

+7 −0
Original line number Diff line number Diff line
@@ -6,4 +6,11 @@ qemu-io: can't open device TEST_DIR/t.qcow2: qcow2 header exceeds cluster size 
no file open, try 'help open'

qemu-io: can't open device TEST_DIR/t.qcow2: qcow2 header exceeds cluster size

no file open, try 'help open'



== Huge unknown header extension ==

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

qemu-io: can't open device TEST_DIR/t.qcow2: Invalid backing file offset

no file open, try 'help open'

qemu-io: can't open device TEST_DIR/t.qcow2: Header extension too large

no file open, try 'help open'

*** done