On Tue, Aug 27, 2019 at 08:01:16AM -0500, Eric Sandeen wrote:
> On 8/26/19 6:15 PM, Dave Chinner wrote:
> > On Mon, Aug 26, 2019 at 02:49:09PM -0700, Darrick J. Wong wrote:
> >> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >>
> >> In xfs_bmbt_diff_two_keys, we perform a signed int64_t subtraction with
> >> two unsigned 64-bit quantities. If the second quantity is actually the
> >> "maximum" key (all ones) as used in _query_all, the subtraction
> >> effectively becomes addition of two positive numbers and the function
> >> returns incorrect results. Fix this with explicit comparisons of the
> >> unsigned values. Nobody needs this now, but the online repair patches
> >> will need this to work properly.
> >>
> >> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >> ---
> >> fs/xfs/libxfs/xfs_bmap_btree.c | 16 ++++++++++++++--
> >> 1 file changed, 14 insertions(+), 2 deletions(-)
> >>
> >>
> >> diff --git a/fs/xfs/libxfs/xfs_bmap_btree.c b/fs/xfs/libxfs/xfs_bmap_btree.c
> >> index fbb18ba5d905..3c1a805b3775 100644
> >> --- a/fs/xfs/libxfs/xfs_bmap_btree.c
> >> +++ b/fs/xfs/libxfs/xfs_bmap_btree.c
> >> @@ -400,8 +400,20 @@ xfs_bmbt_diff_two_keys(
> >> union xfs_btree_key *k1,
> >> union xfs_btree_key *k2)
> >> {
> >> - return (int64_t)be64_to_cpu(k1->bmbt.br_startoff) -
> >> - be64_to_cpu(k2->bmbt.br_startoff);
> >> + uint64_t a = be64_to_cpu(k1->bmbt.br_startoff);
> >> + uint64_t b = be64_to_cpu(k2->bmbt.br_startoff);
> >> +
> >> + /*
> >> + * Note: This routine previously casted a and b to int64 and subtracted
> >> + * them to generate a result. This lead to problems if b was the
> >> + * "maximum" key value (all ones) being signed incorrectly, hence this
> >> + * somewhat less efficient version.
> >> + */
> >> + if (a > b)
> >> + return 1;
> >> + else if (b > a)
> >> + return -1;
> >
> > No need for an else here, but otherwise OK.
> >
> > Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
>
> In fact having the else means the a == b case isn't handled, even if it
> should never happen, so might a static checker eventually complain about
> reaching the end of a non-void function?
Hmm? There's a return 0 after that which Dave's reply clipped.
--D
> -Eric
>
