linux-kernel - Re: [PATCH] st: fix race in st_scsi_execute

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Date:	Fri, 21 Oct 2011 20:00:54 +0300 (EEST)
From:	Kai Makisara <Kai.Makisara@...umbus.fi>
To:	Petr Uzel <petr.uzel@...e.cz>
cc:	linux-kernel@...r.kernel.org, Willem Riede <osst@...de.org>,
	jack@...e.cz, linux-scsi@...r.kernel.org,
	juergen.gross@...fujitsu.com
Subject: Re: [PATCH] st: fix race in st_scsi_execute_end

On Fri, 21 Oct 2011, Petr Uzel wrote:

> The call to complete() in st_scsi_execute_end() wakes up sleeping thread
> in write_behind_check(), which frees the st_request, thus invalidating
> the pointer to the associated bio structure, which is then passed to the
> blk_rq_unmap_user(). Fix by storing pointer to bio structure into
> temporary local variable.
> 
> This bug is present since at least linux-2.6.32.
> 
> CC: stable@...nel.org
> Signed-off-by: Petr Uzel <petr.uzel@...e.cz>
> Reported-by: Juergen Groß <juergen.gross@...fujitsu.com>
> Reviewed-by: Jan Kara <jack@...e.cz>

Acked-by: Kai Mäkisara <kai.makisara@...umbus.fi>

> ---
>  drivers/scsi/st.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
> index 1871b8a..9b28f39 100644
> --- a/drivers/scsi/st.c
> +++ b/drivers/scsi/st.c
> @@ -462,14 +462,16 @@ static void st_scsi_execute_end(struct request *req, int uptodate)
>  {
>  	struct st_request *SRpnt = req->end_io_data;
>  	struct scsi_tape *STp = SRpnt->stp;
> +	struct bio *tmp;
>  
>  	STp->buffer->cmdstat.midlevel_result = SRpnt->result = req->errors;
>  	STp->buffer->cmdstat.residual = req->resid_len;
>  
> +	tmp = SRpnt->bio;
>  	if (SRpnt->waiting)
>  		complete(SRpnt->waiting);
>  
> -	blk_rq_unmap_user(SRpnt->bio);
> +	blk_rq_unmap_user(tmp);
>  	__blk_put_request(req->q, req);
>  }
>  
> 

Thanks for the fix.

Kai