linux-kernel - Re: [PATCH 1/3] aio: Fix a null pointer deref in batch_complete

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Message-ID: <CAJd=RBBFxLeSporsG9xZH=g9G1xCvsmFuu1uQr0CtOa2YntDVA@mail.gmail.com>
Date:	Fri, 25 Jan 2013 21:15:37 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	akpm@...ux-foundation.org, Valdis.Kletnieks@...edu, bcrl@...ck.org,
	zab@...bo.net, linux-kernel@...r.kernel.org, linux-aio@...ck.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/3] aio: Fix a null pointer deref in batch_complete_aio

On Fri, Jan 25, 2013 at 5:43 AM, Kent Overstreet <koverstreet@...gle.com> wrote:
> The batch completion code was trying to be a bit too clever, and skip
> checking ctx where it couldn't be NULL - but that broke if a kiocb had
> been cancelled. Move the check to kioctx_ring_unlock().
>
> Reported-by: Valdis Kletnieks <Valdis.Kletnieks@...edu>
> Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
> ---

Acked-by: Hillf Danton <dhillf@...il.com>

>  fs/aio.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 62573d3..0d2f39d 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -683,6 +683,9 @@ static inline void kioctx_ring_unlock(struct kioctx *ctx, unsigned tail)
>  {
>         struct aio_ring *ring;
>
> +       if (!ctx)
> +               return;
> +
>         smp_wmb();
>         /* make event visible before updating tail */
>
> @@ -760,8 +763,7 @@ void batch_complete_aio(struct batch_complete *batch)
>                 }
>
>                 if (unlikely(req->ki_ctx != ctx)) {
> -                       if (ctx)
> -                               kioctx_ring_unlock(ctx, tail);
> +                       kioctx_ring_unlock(ctx, tail);
>
>                         ctx = req->ki_ctx;
>                         tail = kioctx_ring_lock(ctx);
> --
> 1.7.12
>
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