linux-kernel - Re: [PATCH 3.10 054/139] direct-io: Prevent NULL pointer access in submit_page

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Date:   Wed, 1 Nov 2017 23:43:26 +0100
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Willy Tarreau <w@....eu>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>, linux@...ck-us.net,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 3.10 054/139] direct-io: Prevent NULL pointer access in submit_page_section

Willy,

On 1 November 2017 at 22:25, Willy Tarreau <w@....eu> wrote:
> From: Andreas Gruenbacher <agruenba@...hat.com>
>
> commit 899f0429c7d3eed886406cd72182bee3b96aa1f9 upstream.
>
> In the code added to function submit_page_section by commit b1058b981,
> sdio->bio can currently be NULL when calling dio_bio_submit.  This then
> leads to a NULL pointer access in dio_bio_submit, so check for a NULL
> bio in submit_page_section before trying to submit it instead.
>
> Fixes xfstest generic/250 on gfs2.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
> Reviewed-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Willy Tarreau <w@....eu>
> ---
>  fs/direct-io.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index e17d919..85485c1 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -760,6 +760,8 @@ out:
>         if (sdio->boundary) {
>                 ret = dio_send_cur_page(dio, sdio, map_bh);
>                 dio_bio_submit(dio, sdio);
> +               if (sdio->bio)
> +                       dio_bio_submit(dio, sdio);
>                 page_cache_release(sdio->cur_page);
>                 sdio->cur_page = NULL;
>         }

this is incorrect; please compare with the upstream commit.

Thanks,
Andreas