On Fri, Mar 31, 2017 at 03:47:39PM +0200, 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.
Will you send a new patch that supercedes this one? Stefan
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