Commit 42eb5817 authored by Kevin Wolf's avatar Kevin Wolf
Browse files

qcow1: Validate L2 table size (CVE-2014-0222) 



Too large L2 table sizes cause unbounded allocations. Images actually
created by qemu-img only have 512 byte or 4k L2 tables.

To keep things consistent with cluster sizes, allow ranges between 512
bytes and 64k (in fact, down to 1 entry = 8 bytes is technically
working, but L2 table sizes smaller than a cluster don't make a lot of
sense).

This also means that the number of bytes on the virtual disk that are
described by the same L2 table is limited to at most 8k * 64k or 2^29,
preventively avoiding any integer overflows.

Cc: qemu-stable@nongnu.org
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Reviewed-by: default avatarBenoit Canet <benoit@irqsave.net>
parent 7159a45b

block/qcow.c

+8 −0
Original line number Diff line number Diff line
@@ -139,6 +139,14 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags, 
        goto fail;

    }



    /* l2_bits specifies number of entries; storing a uint64_t in each entry,

     * so bytes = num_entries << 3. */

    if (header.l2_bits < 9 - 3 || header.l2_bits > 16 - 3) {

        error_setg(errp, "L2 table size must be between 512 and 64k");

        ret = -EINVAL;

        goto fail;

    }



    if (header.crypt_method > QCOW_CRYPT_AES) {

        error_setg(errp, "invalid encryption method in qcow header");

        ret = -EINVAL;

tests/qemu-iotests/092

+15 −0
Original line number Diff line number Diff line
@@ -44,6 +44,7 @@ _supported_proto generic 
_supported_os Linux



offset_cluster_bits=32

offset_l2_bits=33



echo

echo "== Invalid cluster size =="
@@ -57,6 +58,20 @@ poke_file "$TEST_IMG" "$offset_cluster_bits" "\x08" 
poke_file "$TEST_IMG" "$offset_cluster_bits" "\x11"

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



echo

echo "== Invalid L2 table size =="

_make_test_img 64M

poke_file "$TEST_IMG" "$offset_l2_bits" "\xff"

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

poke_file "$TEST_IMG" "$offset_l2_bits" "\x05"

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

poke_file "$TEST_IMG" "$offset_l2_bits" "\x0e"

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



# 1 << 0x1b = 2^31 / L2_CACHE_SIZE

poke_file "$TEST_IMG" "$offset_l2_bits" "\x1b"

{ $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/092.out

+11 −0
Original line number Diff line number Diff line
@@ -10,4 +10,15 @@ qemu-io: can't open device TEST_DIR/t.qcow: Cluster size must be between 512 and 
no file open, try 'help open'

qemu-io: can't open device TEST_DIR/t.qcow: Cluster size must be between 512 and 64k

no file open, try 'help open'



== Invalid L2 table size ==

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

qemu-io: can't open device TEST_DIR/t.qcow: L2 table size must be between 512 and 64k

no file open, try 'help open'

qemu-io: can't open device TEST_DIR/t.qcow: L2 table size must be between 512 and 64k

no file open, try 'help open'

qemu-io: can't open device TEST_DIR/t.qcow: L2 table size must be between 512 and 64k

no file open, try 'help open'

qemu-io: can't open device TEST_DIR/t.qcow: L2 table size must be between 512 and 64k

no file open, try 'help open'

*** done