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

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Date:   Wed, 18 Mar 2020 08:53:07 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Allison Randal <allison@...utok.net>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-crypto <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] async_tx: fix possible negative array indexing

On Wed, Mar 18, 2020 at 12:17 AM Rayagonda Kokatanur
<rayagonda.kokatanur@...adcom.com> wrote:
>
> On Tue, Mar 17, 2020 at 11:06 PM Dan Williams <dan.j.williams@...el.com> wrote:
> >
> > On Mon, Mar 16, 2020 at 11:16 PM Rayagonda Kokatanur
> > <rayagonda.kokatanur@...adcom.com> wrote:
> > >
> > > Fix possible negative array index read in __2data_recov_5() function.
> > >
> > > Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
> > > ---
> > >  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().