block: Catch integer overflow in bdrv_rw_co()

Insanely large requests could cause an integer overflow in
bdrv_rw_co() while converting sectors to bytes. This patch catches the
problem and returns an error (if we hadn't overflown the integer here,
bdrv_check_byte_request() would have rejected the request, so we're not
breaking anything that was supposed to work before).

We actually do have a test case that triggers behaviour where we
accidentally let such a request pass, so that it would return success,
but read 0 bytes instead of the requested 4 GB. It fails now like it
should.

If the vdi block driver wants to be able to deal with huge images, it
can't read the whole block bitmap at once into memory like it does
today, but needs to use a metadata cache like qcow2 does.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 5 insertions, 4 deletions

diff --git a/block.c b/block.c
index 5a0b421655..ec3fa503df 100644
--- a/block.c
+++ b/block.c
@@ -2690,6 +2690,10 @@ static int bdrv_rw_co(BlockDriverState *bs, int64_t sector_num, uint8_t *buf,
         .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
     };
 
+    if (nb_sectors < 0 || nb_sectors > INT_MAX / BDRV_SECTOR_SIZE) {
+        return -EINVAL;
+    }
+
     qemu_iovec_init_external(&qiov, &iov, 1);
     return bdrv_prwv_co(bs, sector_num << BDRV_SECTOR_BITS,
                         &qiov, is_write, flags);
diff --git a/tests/qemu-iotests/084.out b/tests/qemu-iotests/084.out
index e681924b85..c7120d9b0b 100644
--- a/tests/qemu-iotests/084.out
+++ b/tests/qemu-iotests/084.out
@@ -4,10 +4,7 @@ QA output created by 084
 
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 
 Test 1: Maximum size (1024 TB):
-image: TEST_DIR/t.IMGFMT
-file format: IMGFMT
-virtual size: 1024T (1125899905794048 bytes)
-cluster_size: 1048576
+qemu-img: Could not open 'TEST_DIR/t.IMGFMT': Could not open 'TEST_DIR/t.IMGFMT': Invalid argument
 
 Test 2: Size too large (1024TB + 1)
 qemu-img: Could not open 'TEST_DIR/t.IMGFMT': Unsupported VDI image size (size is 0x3fffffff10000, max supported is 0x3fffffff00000)