linux-kernel - Re: [PATCH] [SCSI] sg: Fix user memory corruption when SG

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Date:	Mon, 5 Aug 2013 16:38:22 -0700
From:	Roland Dreier <roland@...nel.org>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	Jens Axboe <axboe@...nel.dk>, Doug Gilbert <dgilbert@...erlog.com>,
	Costa Sapuntzakis <costa@...estorage.com>,
	Jörn Engel <joern@...estorage.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH] [SCSI] sg: Fix user memory corruption when SG_IO is
 interrupted by a signal

On Mon, Aug 5, 2013 at 4:31 PM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> I agree with the analysis.  The fix is a bit draconian, though.  A
> workqueue actually runs in a kernel thread and there's a simple test for
> that (!current->mm), so how about this instead (which is much less
> intrusive)

> ---

> diff --git a/fs/bio.c b/fs/bio.c
> index 94bbc04..e2ab39c 100644
> --- a/fs/bio.c
> +++ b/fs/bio.c
> @@ -1045,12 +1045,22 @@ static int __bio_copy_iov(struct bio *bio, struct bio_vec *iovecs,
>  int bio_uncopy_user(struct bio *bio)
>  {
>         struct bio_map_data *bmd = bio->bi_private;
> -       int ret = 0;
> +       struct bio_vec *bvec;
> +       int ret = 0, i;
>
> -       if (!bio_flagged(bio, BIO_NULL_MAPPED))
> -               ret = __bio_copy_iov(bio, bmd->iovecs, bmd->sgvecs,
> -                                    bmd->nr_sgvecs, bio_data_dir(bio) == READ,
> -                                    0, bmd->is_our_pages);
> +       if (!bio_flagged(bio, BIO_NULL_MAPPED)) {
> +               /*
> +                * if we're in a workqueue, the request is orphaned, so
> +                * don't copy into the kernel address space, just free
> +                */
> +               if (current->mm)
> +                       ret = __bio_copy_iov(bio, bmd->iovecs, bmd->sgvecs,
> +                                            bmd->nr_sgvecs, bio_data_dir(bio) == READ,
> +                                            0, bmd->is_our_pages);
> +               else if (bmd->is_our_pages)
> +                       bio_for_each_segment_all(bvec, bio, i)
> +                               __free_page(bvec->bv_page);
> +       }
>         bio_free_map_data(bmd);
>         bio_put(bio);
>         return ret;

Yes, looks reasonable -- I can't think of any reason why anyone would
ever want the bio code to copy to a random userspace address space.

Acked-by: Roland Dreier <roland@...estorage.com>
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