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

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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: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
This commit is contained in:
Kevin Wolf 2014-05-15 16:10:11 +02:00
parent 7159a45b2b
commit 42eb58179b
3 changed files with 34 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
block/qcow.c
View File

@ -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;

15
tests/qemu-iotests/092
View File

@ -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

11
tests/qemu-iotests/092.out
View File

@ -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