Re: [PATCH 1/4] block-crypto-fallback: use a bio_set for splitting bios

[Satya Tangirala <satyat@google.com>]

On Wed, Feb 24, 2021 at 08:24:04AM +0100, Christoph Hellwig wrote:
> bio_split with a NULL bs argumen used to fall back to kmalloc the
> bio, which does not guarantee forward progress and could to deadlocks.
> Now that the overloading of the NULL bs argument to bio_alloc_bioset
> has been removed it crashes instead.  Fix all that by using a special
> crafted bioset.
> 
> Fixes: 3175199ab0ac ("block: split bio_kmalloc from bio_alloc_bioset")
> Reported-by: John Stultz <john.stultz@linaro.org>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Tested-by: John Stultz <john.stultz@linaro.org>
> ---
>  block/blk-crypto-fallback.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-crypto-fallback.c b/block/blk-crypto-fallback.c
> index e8327c50d7c9f4..c176b7af56a7a5 100644
> --- a/block/blk-crypto-fallback.c
> +++ b/block/blk-crypto-fallback.c
> @@ -80,6 +80,7 @@ static struct blk_crypto_keyslot {
>  static struct blk_keyslot_manager blk_crypto_ksm;
>  static struct workqueue_struct *blk_crypto_wq;
>  static mempool_t *blk_crypto_bounce_page_pool;
> +static struct bio_set crypto_bio_split;
>  
>  /*
>   * This is the key we set when evicting a keyslot. This *should* be the all 0's
> @@ -224,7 +225,8 @@ static bool blk_crypto_split_bio_if_needed(struct bio **bio_ptr)
>  	if (num_sectors < bio_sectors(bio)) {
>  		struct bio *split_bio;
>  
> -		split_bio = bio_split(bio, num_sectors, GFP_NOIO, NULL);
> +		split_bio = bio_split(bio, num_sectors, GFP_NOIO,
> +				      &crypto_bio_split);
>  		if (!split_bio) {
>  			bio->bi_status = BLK_STS_RESOURCE;
>  			return false;
> @@ -538,9 +540,13 @@ static int blk_crypto_fallback_init(void)
>  
>  	prandom_bytes(blank_key, BLK_CRYPTO_MAX_KEY_SIZE);
>  
> -	err = blk_ksm_init(&blk_crypto_ksm, blk_crypto_num_keyslots);
> +	err = bioset_init(&crypto_bio_split, 64, 0, 0);
>  	if (err)
>  		goto out;
> +
> +	err = blk_ksm_init(&blk_crypto_ksm, blk_crypto_num_keyslots);
> +	if (err)
> +		goto fail_free_bioset;
>  	err = -ENOMEM;
>  
>  	blk_crypto_ksm.ksm_ll_ops = blk_crypto_ksm_ll_ops;
> @@ -591,6 +597,8 @@ static int blk_crypto_fallback_init(void)
>  	destroy_workqueue(blk_crypto_wq);
>  fail_free_ksm:
>  	blk_ksm_destroy(&blk_crypto_ksm);
> +fail_free_bioset:
> +	bioset_exit(&crypto_bio_split);
>  out:
>  	return err;
>  }
> -- 
> 2.29.2
> 
Thanks for fixing this! If needed, feel free to add
Reviewed-by: Satya Tangirala <satyat@google.com>