Re: [PATCH v1 2/2] async_tx: fix possible negative array indexing

[Dan Williams]

On Wed, Mar 18, 2020 at 12:17 AM Rayagonda Kokatanur
<rayagonda.kokatanur@xxxxxxxxxxxx> wrote:
>
> On Tue, Mar 17, 2020 at 11:06 PM Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> >
> > On Mon, Mar 16, 2020 at 11:16 PM Rayagonda Kokatanur
> > <rayagonda.kokatanur@xxxxxxxxxxxx> wrote:
> > >
> > > Fix possible negative array index read in __2data_recov_5() function.
> > >
> > > Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@xxxxxxxxxxxx>
> > > ---
> > >  crypto/async_tx/async_raid6_recov.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/crypto/async_tx/async_raid6_recov.c b/crypto/async_tx/async_raid6_recov.c
> > > index 33f2a8f8c9f4..9cd016cb2d09 100644
> > > --- a/crypto/async_tx/async_raid6_recov.c
> > > +++ b/crypto/async_tx/async_raid6_recov.c
> > > @@ -206,7 +206,7 @@ __2data_recov_5(int disks, size_t bytes, int faila, int failb,
> > >                 good_srcs++;
> > >         }
> > >
> > > -       if (good_srcs > 1)
> > > +       if ((good_srcs > 1) || (good < 0))
> > >                 return NULL;
> >
> > Read the code again, I don't see how this can happen.
>
> This case can happen and it is reported by coverity tool.
> In the for loop , the condition "if (blocks[i] == NULL)" true all the
> time then variable 'good' will be -1.

Just because coverity reports it does not make it true. Please go read
the full call path that gets us to this call and identify how all
entries in blocks[] could be NULL. Hint, the answer is in how
async_raid6_2data_recov() calls __2data_recov_5().