Subject: Re: [PATCH v3 12/18] crypto: switch af_alg_make_sg() to iov_iter

From: Stephan Mueller <[email-masked]>
Date: Mon, 09 Feb 2015 14:33:48 +0100

Am Mittwoch, 4. Februar 2015, 06:40:03 schrieb Al Viro:

Hi Al,

> From: Al Viro <[email-masked]>
> 
> With that, all ->sendmsg() instances are converted to iov_iter primitives
> and are agnostic wrt the kind of iov_iter they are working with.
> So's the last remaining ->recvmsg() instance that wasn't kind-agnostic yet.
> All ->sendmsg() and ->recvmsg() advance ->msg_iter by the amount actually
> copied and none of them modifies the underlying iovec, etc.
> 
> Cc: [email-masked]
> Signed-off-by: Al Viro <[email-masked]>
> ---
>  crypto/af_alg.c         | 40 ++++++++------------------
>  crypto/algif_hash.c     | 45 ++++++++++++------------------
>  crypto/algif_skcipher.c | 74
> ++++++++++++++++++++++--------------------------- include/crypto/if_alg.h |
>  3 +-
>  4 files changed, 62 insertions(+), 100 deletions(-)
> 
> diff --git a/crypto/af_alg.c b/crypto/af_alg.c
> index 4665b79c..eb78fe8 100644
> --- a/crypto/af_alg.c
> +++ b/crypto/af_alg.c
> @@ -338,49 +338,31 @@ static const struct net_proto_family alg_family = {
>  	.owner	=	THIS_MODULE,
>  };
> 
> -int af_alg_make_sg(struct af_alg_sgl *sgl, void __user *addr, int len,
> -		   int write)
> +int af_alg_make_sg(struct af_alg_sgl *sgl, struct iov_iter *iter, int len)

Shouldn't len be size_t? iov_iter_get_pages wants a size_t. Also, the 
invocation of af_alg_make_sg uses an unsigned variable that is provided by 
userspace.
>  {
> -	unsigned long from = (unsigned long)addr;
> -	unsigned long npages;
> -	unsigned off;
> -	int err;
> -	int i;
> -
> -	err = -EFAULT;
> -	if (!access_ok(write ? VERIFY_READ : VERIFY_WRITE, addr, len))
> -		goto out;
> -
> -	off = from & ~PAGE_MASK;
> -	npages = (off + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
> -	if (npages > ALG_MAX_PAGES)
> -		npages = ALG_MAX_PAGES;
> +	size_t off;
> +	ssize_t n;
> +	int npages, i;
> 
> -	err = get_user_pages_fast(from, npages, write, sgl->pages);
> -	if (err < 0)
> -		goto out;
> +	n = iov_iter_get_pages(iter, sgl->pages, len, ALG_MAX_PAGES, &off);
> +	if (n < 0)
> +		return n;
> 
> -	npages = err;
> -	err = -EINVAL;
> +	npages = PAGE_ALIGN(off + n);
>  	if (WARN_ON(npages == 0))
> -		goto out;
> -
> -	err = 0;
> +		return -EINVAL;
> 
>  	sg_init_table(sgl->sg, npages);
> 
> -	for (i = 0; i < npages; i++) {
> +	for (i = 0, len = n; i < npages; i++) {
>  		int plen = min_t(int, len, PAGE_SIZE - off);
> 
>  		sg_set_page(sgl->sg + i, sgl->pages[i], plen, off);
> 
>  		off = 0;
>  		len -= plen;
> -		err += plen;
>  	}
> -
> -out:
> -	return err;
> +	return n;
>  }
>  EXPORT_SYMBOL_GPL(af_alg_make_sg);
> 
> diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
> index 01f56eb..01da360 100644
> --- a/crypto/algif_hash.c
> +++ b/crypto/algif_hash.c
> @@ -41,8 +41,6 @@ static int hash_sendmsg(struct kiocb *unused, struct
> socket *sock, struct sock *sk = sock->sk;
>  	struct alg_sock *ask = alg_sk(sk);
>  	struct hash_ctx *ctx = ask->private;
> -	unsigned long iovlen;
> -	const struct iovec *iov;
>  	long copied = 0;
>  	int err;
> 
> @@ -58,37 +56,28 @@ static int hash_sendmsg(struct kiocb *unused, struct
> socket *sock,
> 
>  	ctx->more = 0;
> 
> -	for (iov = msg->msg_iter.iov, iovlen = msg->msg_iter.nr_segs; iovlen > 
0;
> -	     iovlen--, iov++) {
> -		unsigned long seglen = iov->iov_len;
> -		char __user *from = iov->iov_base;
> +	while (iov_iter_count(&msg->msg_iter)) {
> +		int len = iov_iter_count(&msg->msg_iter);

size_t for len?

> 
> -		while (seglen) {
> -			int len = min_t(unsigned long, seglen, limit);
> -			int newlen;
> +		if (len > limit)
> +			len = limit;

If we leave int, do we have a wrap problem here?
> 
> -			newlen = af_alg_make_sg(&ctx->sgl, from, len, 0);
> -			if (newlen < 0) {
> -				err = copied ? 0 : newlen;
> -				goto unlock;
> -			}
> -
> -			ahash_request_set_crypt(&ctx->req, ctx->sgl.sg, NULL,
> -						newlen);
> -
> -			err = af_alg_wait_for_completion(
> -				crypto_ahash_update(&ctx->req),
> -				&ctx->completion);
> +		len = af_alg_make_sg(&ctx->sgl, &msg->msg_iter, len);
> +		if (len < 0) {
> +			err = copied ? 0 : len;
> +			goto unlock;
> +		}
> 
> -			af_alg_free_sg(&ctx->sgl);
> +		ahash_request_set_crypt(&ctx->req, ctx->sgl.sg, NULL, len);
> 
> -			if (err)
> -				goto unlock;
> +		err = af_alg_wait_for_completion(crypto_ahash_update(&ctx-
>req),
> +						 &ctx->completion);
> +		af_alg_free_sg(&ctx->sgl);
> +		if (err)
> +			goto unlock;
> 
> -			seglen -= newlen;
> -			from += newlen;
> -			copied += newlen;
> -		}
> +		copied += len;
> +		iov_iter_advance(&msg->msg_iter, len);
>  	}
> 
>  	err = 0;
> diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
> index c12207c..37110fd 100644
> --- a/crypto/algif_skcipher.c
> +++ b/crypto/algif_skcipher.c
> @@ -426,67 +426,59 @@ static int skcipher_recvmsg(struct kiocb *unused,
> struct socket *sock, &ctx->req));
>  	struct skcipher_sg_list *sgl;
>  	struct scatterlist *sg;
> -	unsigned long iovlen;
> -	const struct iovec *iov;
>  	int err = -EAGAIN;
>  	int used;
>  	long copied = 0;
> 
>  	lock_sock(sk);
> -	for (iov = msg->msg_iter.iov, iovlen = msg->msg_iter.nr_segs; iovlen > 
0;
> -	     iovlen--, iov++) {
> -		unsigned long seglen = iov->iov_len;
> -		char __user *from = iov->iov_base;
> -
> -		while (seglen) {
> -			sgl = list_first_entry(&ctx->tsgl,
> -					       struct skcipher_sg_list, list);
> -			sg = sgl->sg;
> -
> -			while (!sg->length)
> -				sg++;
> -
> -			if (!ctx->used) {
> -				err = skcipher_wait_for_data(sk, flags);
> -				if (err)
> -					goto unlock;
> -			}
> +	while (iov_iter_count(&msg->msg_iter)) {
> +		sgl = list_first_entry(&ctx->tsgl,
> +				       struct skcipher_sg_list, list);
> +		sg = sgl->sg;
> 
> -			used = min_t(unsigned long, ctx->used, seglen);
> +		while (!sg->length)
> +			sg++;
> 
> -			used = af_alg_make_sg(&ctx->rsgl, from, used, 1);
> -			err = used;
> -			if (err < 0)
> +		used = ctx->used;
> +		if (!used) {

I do not think that this change is correct. The following 
skcipher_wait_for_data puts the recvmsg to sleep. That means, ctx->used may 
change due to a new sendmsg() while sleeping.

Hence, I would think that we should leave the code as it was:

if (!ctx->used)

and then in the following

> +			err = skcipher_wait_for_data(sk, flags);
> +			if (err)
>  				goto unlock;
> +		}
> +
> +		used = min_t(unsigned long, used, iov_iter_count(&msg-
>msg_iter));

we use ctx->used here.

And shouldn't we use size_t here instead of unsigned long?

> +
> +		used = af_alg_make_sg(&ctx->rsgl, &msg->msg_iter, used);
> +		err = used;
> +		if (err < 0)
> +			goto unlock;
> 
> -			if (ctx->more || used < ctx->used)
> -				used -= used % bs;
> +		if (ctx->more || used < ctx->used)
> +			used -= used % bs;
> 
> -			err = -EINVAL;
> -			if (!used)
> -				goto free;
> +		err = -EINVAL;
> +		if (!used)
> +			goto free;
> 
> -			ablkcipher_request_set_crypt(&ctx->req, sg,
> -						     ctx->rsgl.sg, used,
> -						     ctx->iv);
> +		ablkcipher_request_set_crypt(&ctx->req, sg,
> +					     ctx->rsgl.sg, used,
> +					     ctx->iv);
> 
> -			err = af_alg_wait_for_completion(
> +		err = af_alg_wait_for_completion(
>  				ctx->enc ?
>  					crypto_ablkcipher_encrypt(&ctx->req) :
>  					crypto_ablkcipher_decrypt(&ctx->req),
>  				&ctx->completion);
> 
>  free:
> -			af_alg_free_sg(&ctx->rsgl);
> +		af_alg_free_sg(&ctx->rsgl);
> 
> -			if (err)
> -				goto unlock;
> +		if (err)
> +			goto unlock;
> 
> -			copied += used;
> -			from += used;
> -			seglen -= used;
> -			skcipher_pull_sgl(sk, used);
> -		}
> +		copied += used;
> +		skcipher_pull_sgl(sk, used);
> +		iov_iter_advance(&msg->msg_iter, used);
>  	}
> 
>  	err = 0;
> diff --git a/include/crypto/if_alg.h b/include/crypto/if_alg.h
> index cd62bf4..88ea64e 100644
> --- a/include/crypto/if_alg.h
> +++ b/include/crypto/if_alg.h
> @@ -67,8 +67,7 @@ int af_alg_unregister_type(const struct af_alg_type
> *type); int af_alg_release(struct socket *sock);
>  int af_alg_accept(struct sock *sk, struct socket *newsock);
> 
> -int af_alg_make_sg(struct af_alg_sgl *sgl, void __user *addr, int len,
> -		   int write);
> +int af_alg_make_sg(struct af_alg_sgl *sgl, struct iov_iter *iter, int len);
> void af_alg_free_sg(struct af_alg_sgl *sgl);
> 
>  int af_alg_cmsg_send(struct msghdr *msg, struct af_alg_control *con);

-- 
Ciao
Stephan