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

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Message-ID: <CAHO=5PE9SLg2O1fp5YUp0Z0sbNfKNiu5kGXBRtHmGyXRW5w3pg@mail.gmail.com>
Date:   Wed, 18 Mar 2020 12:47:09 +0530
From:   Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
To:     Dan Williams <dan.j.williams@...el.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 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.