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From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 12 Mar 2020 13:06:23 +0100
Message-ID: <CAG_fn=WP0xeCaWpWzhzvT-uxW4w1dvVvxZ=yBGKGTNFwjD=gJw@mail.gmail.com>
Subject: Re: [PATCH] lib/stackdepot.c: fix a condition in stack_depot_fetch()
To:     Dan Carpenter <dan.carpenter@oracle.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Miles Chen <miles.chen@mediatek.com>,
        LKML <linux-kernel@vger.kernel.org>,
        kernel-janitors@vger.kernel.org
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On Thu, Mar 12, 2020 at 12:30 PM Dan Carpenter <dan.carpenter@oracle.com> w=
rote:
>
> We should check for a NULL pointer first before adding the offset.
> Otherwise if the pointer is NULL and the offset is non-zero, it will
> lead to an Oops.

 Thanks!

> Fixes: d45048e65a59 ("lib/stackdepot.c: check depot_index before accessin=
g the stack slab")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

Acked-by: Alexander Potapenko <glider@google.com>

> ---
>  lib/stackdepot.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index da5d1880bf34..2caffc64e4c8 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -207,18 +207,16 @@ unsigned int stack_depot_fetch(depot_stack_handle_t=
 handle,
>         size_t offset =3D parts.offset << STACK_ALLOC_ALIGN;
>         struct stack_record *stack;
>
> +       *entries =3D NULL;
>         if (parts.slabindex > depot_index) {
>                 WARN(1, "slab index %d out of bounds (%d) for stack id %0=
8x\n",
>                         parts.slabindex, depot_index, handle);
> -               *entries =3D NULL;
>                 return 0;
>         }
>         slab =3D stack_slabs[parts.slabindex];
> -       stack =3D slab + offset;
> -       if (!stack) {
> -               *entries =3D NULL;
> +       if (!slab)
>                 return 0;
> -       }
> +       stack =3D slab + offset;
>
>         *entries =3D stack->entries;
>         return stack->size;
> --
> 2.20.1
>


--=20
Alexander Potapenko
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