Re: [PATCH -next] btrfs: Fix type conversion in btrfs_read_root_item

Dan Carpenter
2019-02-20T06:10:42Z

On Wed, Feb 20, 2019 at 08:58:43AM +0300, Dan Carpenter wrote:
> On Wed, Feb 20, 2019 at 03:08:40AM +0000, YueHaibing wrote:
> > btrfs_item_size_nr return value is u32, convert it to int may result
> > in truncation.Also read_extent_buffer expect a unsigned param, so
> > min_t should use type u32 to compare.
> >
> > Fixes: 8ea05e3a4262 ("Btrfs: introduce subvol uuids and times")
> > Signed-off-by: YueHaibing <yuehaibing@huawei.com>
> > ---
> > fs/btrfs/root-tree.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
> > index 02d1a57af78b..893d12fbfda0 100644
> > --- a/fs/btrfs/root-tree.c
> > +++ b/fs/btrfs/root-tree.c
> > @@ -21,12 +21,12 @@ static void btrfs_read_root_item(struct extent_buffer *eb, int slot,
> > struct btrfs_root_item *item)
> > {
> > uuid_le uuid;
> > - int len;
> > + u32 len;
> > int need_reset = 0;
> >
> > len = btrfs_item_size_nr(eb, slot);
> > read_extent_buffer(eb, item, btrfs_item_ptr_offset(eb, slot),
> > - min_t(int, len, (int)sizeof(*item)));
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Yeah, min_t() should normally cast to unsigned and the extra cast is
> silly.
>

Btw, I shouldn't have had to dig through the patch to find the *real*
reason you wrote it. A better description would have said:

There is a messy cast here:

min_t(int, len, (int)sizeof(*item)));

min_t() should normally cast to unsigned. It's not possible for
"len" to be negative, but if it were then then we definitely
wouldn't want to pass negatives to read_extent_buffer(). Also there
is an extra cast.

This patch shouldn't affect runtime, it's just a clean up.

regards,
dan carpenter