On Mon, Aug 5, 2013 at 4:31 PM, James Bottomley
<James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
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