On 03/31/2017 04:47 PM, Max Reitz wrote: > On 31.03.2017 15:13, Peter Maydell wrote: >> Coverity (CID 1307776) points out that in the multiply: >> space = to_allocate * s->tracks; >> we are trying to calculate a 64 bit result but the types >> of to_allocate and s->tracks mean that we actually calculate >> a 32 bit result. Add an explicit cast to force a 64 bit >> multiply. >> >> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> >> --- >> NB: compile-and-make-check tested only... >> --- >> block/parallels.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/block/parallels.c b/block/parallels.c >> index 4173b3f..3886c30 100644 >> --- a/block/parallels.c >> +++ b/block/parallels.c >> @@ -206,7 +206,7 @@ static int64_t allocate_clusters(BlockDriverState *bs, >> int64_t sector_num, >> } >> >> to_allocate = DIV_ROUND_UP(sector_num + *pnum, s->tracks) - idx; >> - space = to_allocate * s->tracks; >> + space = (int64_t)to_allocate * s->tracks; >> if (s->data_end + space > bdrv_getlength(bs->file->bs) >> >> BDRV_SECTOR_BITS) { >> int ret; >> space += s->prealloc_size; > I think the division is technically fine because to_allocate will > roughly be *pnum / s->tracks (and since *pnum is an int, the > multiplication cannot overflow). > > However, it's still good to fix this, but I would do it differently: > Make idx, to_allocate, and i all uint64_t or int64_t instead of > uint32_t. This would also prevent accidental overflow when storing the > result of the division in: > > idx = sector_num / s->tracks; > if (idx >= s->bat_size) { > [...] > > The much greater problem to me appears to be that we don't check that > idx + to_allocate <= s->bat_size. I'm not sure whether there can be a > buffer overflow in the for loop below, but I'm not sure I really want to > know either... I think the block_status() call limits *pnum so that > there will not be an overflow, but then we should at least assert this. > > Max > technically we are protected by the check in
static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child, BdrvTrackedRequest *req, int64_t offset, unsigned int bytes, int64_t align, QEMUIOVector *qiov, int flags) ... /* Forward the request to the BlockDriver, possibly fragmenting it */ total_bytes = bdrv_getlength(bs); if (total_bytes < 0) { ret = total_bytes; goto out; } max_bytes = ROUND_UP(MAX(0, total_bytes - offset), align); if (bytes <= max_bytes && bytes <= max_transfer) { ret = bdrv_driver_preadv(bs, offset, bytes, qiov, 0); goto out; } which guarantees that the request is always inside the length of the device. Thus we should be on the safe side with the mentioned access as bat_size is calculated from the size of the entire virtual disk. Den