crypto: af_alg - consolidation of duplicate code

Consolidate following data structures:

skcipher_async_req, aead_async_req -> af_alg_async_req
skcipher_rsgl, aead_rsql -> af_alg_rsgl
skcipher_tsgl, aead_tsql -> af_alg_tsgl
skcipher_ctx, aead_ctx -> af_alg_ctx

Consolidate following functions:

skcipher_sndbuf, aead_sndbuf -> af_alg_sndbuf
skcipher_writable, aead_writable -> af_alg_writable
skcipher_rcvbuf, aead_rcvbuf -> af_alg_rcvbuf
skcipher_readable, aead_readable -> af_alg_readable
aead_alloc_tsgl, skcipher_alloc_tsgl -> af_alg_alloc_tsgl
aead_count_tsgl, skcipher_count_tsgl -> af_alg_count_tsgl
aead_pull_tsgl, skcipher_pull_tsgl -> af_alg_pull_tsgl
aead_free_areq_sgls, skcipher_free_areq_sgls -> af_alg_free_areq_sgls
aead_wait_for_wmem, skcipher_wait_for_wmem -> af_alg_wait_for_wmem
aead_wmem_wakeup, skcipher_wmem_wakeup -> af_alg_wmem_wakeup
aead_wait_for_data, skcipher_wait_for_data -> af_alg_wait_for_data
aead_data_wakeup, skcipher_data_wakeup -> af_alg_data_wakeup
aead_sendmsg, skcipher_sendmsg -> af_alg_sendmsg
aead_sendpage, skcipher_sendpage -> af_alg_sendpage
aead_async_cb, skcipher_async_cb -> af_alg_async_cb
aead_poll, skcipher_poll -> af_alg_poll

Split out the following common code from recvmsg:

af_alg_alloc_areq: allocation of the request data structure for the
cipher operation

af_alg_get_rsgl: creation of the RX SGL anchored in the request data
structure

The following changes to the implementation without affecting the
functionality have been applied to synchronize slightly different code
bases in algif_skcipher and algif_aead:

The wakeup in af_alg_wait_for_data is triggered when either more data
is received or the indicator that more data is to be expected is
released. The first is triggered by user space, the second is
triggered by the kernel upon finishing the processing of data
(i.e. the kernel is ready for more).

af_alg_sendmsg uses size_t in min_t calculation for obtaining len.
Return code determination is consistent with algif_skcipher. The
scope of the variable i is reduced to match algif_aead. The type of the
variable i is switched from int to unsigned int to match algif_aead.

af_alg_sendpage does not contain the superfluous err = 0 from
aead_sendpage.

af_alg_async_cb requires to store the number of output bytes in
areq->outlen before the AIO callback is triggered.

The POLLIN / POLLRDNORM is now set when either not more data is given or
the kernel is supplied with data. This is consistent to the wakeup from
sleep when the kernel waits for data.

The request data structure is extended by the field last_rsgl which
points to the last RX SGL list entry. This shall help recvmsg
implementation to chain the RX SGL to other SG(L)s if needed. It is
currently used by algif_aead which chains the tag SGL to the RX SGL
during decryption.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 693 insertions, 0 deletions

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 92a3d540d920..d6936c0e08d9 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -21,6 +21,7 @@
 #include <linux/module.h>
 #include <linux/net.h>
 #include <linux/rwsem.h>
+#include <linux/sched/signal.h>
 #include <linux/security.h>
 
 struct alg_type_list {
@@ -507,6 +508,698 @@ void af_alg_complete(struct crypto_async_request *req, int err)
 }
 EXPORT_SYMBOL_GPL(af_alg_complete);
 
+/**
+ * af_alg_alloc_tsgl - allocate the TX SGL
+ *
+ * @sk socket of connection to user space
+ * @return: 0 upon success, < 0 upon error
+ */
+int af_alg_alloc_tsgl(struct sock *sk)
+{
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	struct af_alg_tsgl *sgl;
+	struct scatterlist *sg = NULL;
+
+	sgl = list_entry(ctx->tsgl_list.prev, struct af_alg_tsgl, list);
+	if (!list_empty(&ctx->tsgl_list))
+		sg = sgl->sg;
+
+	if (!sg || sgl->cur >= MAX_SGL_ENTS) {
+		sgl = sock_kmalloc(sk, sizeof(*sgl) +
+				       sizeof(sgl->sg[0]) * (MAX_SGL_ENTS + 1),
+				   GFP_KERNEL);
+		if (!sgl)
+			return -ENOMEM;
+
+		sg_init_table(sgl->sg, MAX_SGL_ENTS + 1);
+		sgl->cur = 0;
+
+		if (sg)
+			sg_chain(sg, MAX_SGL_ENTS + 1, sgl->sg);
+
+		list_add_tail(&sgl->list, &ctx->tsgl_list);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(af_alg_alloc_tsgl);
+
+/**
+ * aead_count_tsgl - Count number of TX SG entries
+ *
+ * The counting starts from the beginning of the SGL to @bytes. If
+ * an offset is provided, the counting of the SG entries starts at the offset.
+ *
+ * @sk socket of connection to user space
+ * @bytes Count the number of SG entries holding given number of bytes.
+ * @offset Start the counting of SG entries from the given offset.
+ * @return Number of TX SG entries found given the constraints
+ */
+unsigned int af_alg_count_tsgl(struct sock *sk, size_t bytes, size_t offset)
+{
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	struct af_alg_tsgl *sgl, *tmp;
+	unsigned int i;
+	unsigned int sgl_count = 0;
+
+	if (!bytes)
+		return 0;
+
+	list_for_each_entry_safe(sgl, tmp, &ctx->tsgl_list, list) {
+		struct scatterlist *sg = sgl->sg;
+
+		for (i = 0; i < sgl->cur; i++) {
+			size_t bytes_count;
+
+			/* Skip offset */
+			if (offset >= sg[i].length) {
+				offset -= sg[i].length;
+				bytes -= sg[i].length;
+				continue;
+			}
+
+			bytes_count = sg[i].length - offset;
+
+			offset = 0;
+			sgl_count++;
+
+			/* If we have seen requested number of bytes, stop */
+			if (bytes_count >= bytes)
+				return sgl_count;
+
+			bytes -= bytes_count;
+		}
+	}
+
+	return sgl_count;
+}
+EXPORT_SYMBOL_GPL(af_alg_count_tsgl);
+
+/**
+ * aead_pull_tsgl - Release the specified buffers from TX SGL
+ *
+ * If @dst is non-null, reassign the pages to dst. The caller must release
+ * the pages. If @dst_offset is given only reassign the pages to @dst starting
+ * at the @dst_offset (byte). The caller must ensure that @dst is large
+ * enough (e.g. by using af_alg_count_tsgl with the same offset).
+ *
+ * @sk socket of connection to user space
+ * @used Number of bytes to pull from TX SGL
+ * @dst If non-NULL, buffer is reassigned to dst SGL instead of releasing. The
+ *	caller must release the buffers in dst.
+ * @dst_offset Reassign the TX SGL from given offset. All buffers before
+ *	       reaching the offset is released.
+ */
+void af_alg_pull_tsgl(struct sock *sk, size_t used, struct scatterlist *dst,
+		      size_t dst_offset)
+{
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	struct af_alg_tsgl *sgl;
+	struct scatterlist *sg;
+	unsigned int i, j;
+
+	while (!list_empty(&ctx->tsgl_list)) {
+		sgl = list_first_entry(&ctx->tsgl_list, struct af_alg_tsgl,
+				       list);
+		sg = sgl->sg;
+
+		for (i = 0, j = 0; i < sgl->cur; i++) {
+			size_t plen = min_t(size_t, used, sg[i].length);
+			struct page *page = sg_page(sg + i);
+
+			if (!page)
+				continue;
+
+			/*
+			 * Assumption: caller created af_alg_count_tsgl(len)
+			 * SG entries in dst.
+			 */
+			if (dst) {
+				if (dst_offset >= plen) {
+					/* discard page before offset */
+					dst_offset -= plen;
+					put_page(page);
+				} else {
+					/* reassign page to dst after offset */
+					sg_set_page(dst + j, page,
+						    plen - dst_offset,
+						    sg[i].offset + dst_offset);
+					dst_offset = 0;
+					j++;
+				}
+			}
+
+			sg[i].length -= plen;
+			sg[i].offset += plen;
+
+			used -= plen;
+			ctx->used -= plen;
+
+			if (sg[i].length)
+				return;
+
+			if (!dst)
+				put_page(page);
+
+			sg_assign_page(sg + i, NULL);
+		}
+
+		list_del(&sgl->list);
+		sock_kfree_s(sk, sgl, sizeof(*sgl) + sizeof(sgl->sg[0]) *
+						     (MAX_SGL_ENTS + 1));
+	}
+
+	if (!ctx->used)
+		ctx->merge = 0;
+}
+EXPORT_SYMBOL_GPL(af_alg_pull_tsgl);
+
+/**
+ * af_alg_free_areq_sgls - Release TX and RX SGLs of the request
+ *
+ * @areq Request holding the TX and RX SGL
+ */
+void af_alg_free_areq_sgls(struct af_alg_async_req *areq)
+{
+	struct sock *sk = areq->sk;
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	struct af_alg_rsgl *rsgl, *tmp;
+	struct scatterlist *tsgl;
+	struct scatterlist *sg;
+	unsigned int i;
+
+	list_for_each_entry_safe(rsgl, tmp, &areq->rsgl_list, list) {
+		ctx->rcvused -= rsgl->sg_num_bytes;
+		af_alg_free_sg(&rsgl->sgl);
+		list_del(&rsgl->list);
+		if (rsgl != &areq->first_rsgl)
+			sock_kfree_s(sk, rsgl, sizeof(*rsgl));
+	}
+
+	tsgl = areq->tsgl;
+	for_each_sg(tsgl, sg, areq->tsgl_entries, i) {
+		if (!sg_page(sg))
+			continue;
+		put_page(sg_page(sg));
+	}
+
+	if (areq->tsgl && areq->tsgl_entries)
+		sock_kfree_s(sk, tsgl, areq->tsgl_entries * sizeof(*tsgl));
+}
+EXPORT_SYMBOL_GPL(af_alg_free_areq_sgls);
+
+/**
+ * af_alg_wait_for_wmem - wait for availability of writable memory
+ *
+ * @sk socket of connection to user space
+ * @flags If MSG_DONTWAIT is set, then only report if function would sleep
+ * @return 0 when writable memory is available, < 0 upon error
+ */
+int af_alg_wait_for_wmem(struct sock *sk, unsigned int flags)
+{
+	DEFINE_WAIT_FUNC(wait, woken_wake_function);
+	int err = -ERESTARTSYS;
+	long timeout;
+
+	if (flags & MSG_DONTWAIT)
+		return -EAGAIN;
+
+	sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
+
+	add_wait_queue(sk_sleep(sk), &wait);
+	for (;;) {
+		if (signal_pending(current))
+			break;
+		timeout = MAX_SCHEDULE_TIMEOUT;
+		if (sk_wait_event(sk, &timeout, af_alg_writable(sk), &wait)) {
+			err = 0;
+			break;
+		}
+	}
+	remove_wait_queue(sk_sleep(sk), &wait);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(af_alg_wait_for_wmem);
+
+/**
+ * af_alg_wmem_wakeup - wakeup caller when writable memory is available
+ *
+ * @sk socket of connection to user space
+ */
+void af_alg_wmem_wakeup(struct sock *sk)
+{
+	struct socket_wq *wq;
+
+	if (!af_alg_writable(sk))
+		return;
+
+	rcu_read_lock();
+	wq = rcu_dereference(sk->sk_wq);
+	if (skwq_has_sleeper(wq))
+		wake_up_interruptible_sync_poll(&wq->wait, POLLIN |
+							   POLLRDNORM |
+							   POLLRDBAND);
+	sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(af_alg_wmem_wakeup);
+
+/**
+ * af_alg_wait_for_data - wait for availability of TX data
+ *
+ * @sk socket of connection to user space
+ * @flags If MSG_DONTWAIT is set, then only report if function would sleep
+ * @return 0 when writable memory is available, < 0 upon error
+ */
+int af_alg_wait_for_data(struct sock *sk, unsigned flags)
+{
+	DEFINE_WAIT_FUNC(wait, woken_wake_function);
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	long timeout;
+	int err = -ERESTARTSYS;
+
+	if (flags & MSG_DONTWAIT)
+		return -EAGAIN;
+
+	sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
+
+	add_wait_queue(sk_sleep(sk), &wait);
+	for (;;) {
+		if (signal_pending(current))
+			break;
+		timeout = MAX_SCHEDULE_TIMEOUT;
+		if (sk_wait_event(sk, &timeout, (ctx->used || !ctx->more),
+				  &wait)) {
+			err = 0;
+			break;
+		}
+	}
+	remove_wait_queue(sk_sleep(sk), &wait);
+
+	sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(af_alg_wait_for_data);
+
+/**
+ * af_alg_data_wakeup - wakeup caller when new data can be sent to kernel
+ *
+ * @sk socket of connection to user space
+ */
+
+void af_alg_data_wakeup(struct sock *sk)
+{
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	struct socket_wq *wq;
+
+	if (!ctx->used)
+		return;
+
+	rcu_read_lock();
+	wq = rcu_dereference(sk->sk_wq);
+	if (skwq_has_sleeper(wq))
+		wake_up_interruptible_sync_poll(&wq->wait, POLLOUT |
+							   POLLRDNORM |
+							   POLLRDBAND);
+	sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(af_alg_data_wakeup);
+
+/**
+ * af_alg_sendmsg - implementation of sendmsg system call handler
+ *
+ * The sendmsg system call handler obtains the user data and stores it
+ * in ctx->tsgl_list. This implies allocation of the required numbers of
+ * struct af_alg_tsgl.
+ *
+ * In addition, the ctx is filled with the information sent via CMSG.
+ *
+ * @sock socket of connection to user space
+ * @msg message from user space
+ * @size size of message from user space
+ * @ivsize the size of the IV for the cipher operation to verify that the
+ *	   user-space-provided IV has the right size
+ * @return the number of copied data upon success, < 0 upon error
+ */
+int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
+		   unsigned int ivsize)
+{
+	struct sock *sk = sock->sk;
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	struct af_alg_tsgl *sgl;
+	struct af_alg_control con = {};
+	long copied = 0;
+	bool enc = 0;
+	bool init = 0;
+	int err = 0;
+
+	if (msg->msg_controllen) {
+		err = af_alg_cmsg_send(msg, &con);
+		if (err)
+			return err;
+
+		init = 1;
+		switch (con.op) {
+		case ALG_OP_ENCRYPT:
+			enc = 1;
+			break;
+		case ALG_OP_DECRYPT:
+			enc = 0;
+			break;
+		default:
+			return -EINVAL;
+		}
+
+		if (con.iv && con.iv->ivlen != ivsize)
+			return -EINVAL;
+	}
+
+	lock_sock(sk);
+	if (!ctx->more && ctx->used) {
+		err = -EINVAL;
+		goto unlock;
+	}
+
+	if (init) {
+		ctx->enc = enc;
+		if (con.iv)
+			memcpy(ctx->iv, con.iv->iv, ivsize);
+
+		ctx->aead_assoclen = con.aead_assoclen;
+	}
+
+	while (size) {
+		struct scatterlist *sg;
+		size_t len = size;
+		size_t plen;
+
+		/* use the existing memory in an allocated page */
+		if (ctx->merge) {
+			sgl = list_entry(ctx->tsgl_list.prev,
+					 struct af_alg_tsgl, list);
+			sg = sgl->sg + sgl->cur - 1;
+			len = min_t(size_t, len,
+				    PAGE_SIZE - sg->offset - sg->length);
+
+			err = memcpy_from_msg(page_address(sg_page(sg)) +
+					      sg->offset + sg->length,
+					      msg, len);
+			if (err)
+				goto unlock;
+
+			sg->length += len;
+			ctx->merge = (sg->offset + sg->length) &
+				     (PAGE_SIZE - 1);
+
+			ctx->used += len;
+			copied += len;
+			size -= len;
+			continue;
+		}
+
+		if (!af_alg_writable(sk)) {
+			err = af_alg_wait_for_wmem(sk, msg->msg_flags);
+			if (err)
+				goto unlock;
+		}
+
+		/* allocate a new page */
+		len = min_t(unsigned long, len, af_alg_sndbuf(sk));
+
+		err = af_alg_alloc_tsgl(sk);
+		if (err)
+			goto unlock;
+
+		sgl = list_entry(ctx->tsgl_list.prev, struct af_alg_tsgl,
+				 list);
+		sg = sgl->sg;
+		if (sgl->cur)
+			sg_unmark_end(sg + sgl->cur - 1);
+
+		do {
+			unsigned int i = sgl->cur;
+
+			plen = min_t(size_t, len, PAGE_SIZE);
+
+			sg_assign_page(sg + i, alloc_page(GFP_KERNEL));
+			if (!sg_page(sg + i)) {
+				err = -ENOMEM;
+				goto unlock;
+			}
+
+			err = memcpy_from_msg(page_address(sg_page(sg + i)),
+					      msg, plen);
+			if (err) {
+				__free_page(sg_page(sg + i));
+				sg_assign_page(sg + i, NULL);
+				goto unlock;
+			}
+
+			sg[i].length = plen;
+			len -= plen;
+			ctx->used += plen;
+			copied += plen;
+			size -= plen;
+			sgl->cur++;
+		} while (len && sgl->cur < MAX_SGL_ENTS);
+
+		if (!size)
+			sg_mark_end(sg + sgl->cur - 1);
+
+		ctx->merge = plen & (PAGE_SIZE - 1);
+	}
+
+	err = 0;
+
+	ctx->more = msg->msg_flags & MSG_MORE;
+
+unlock:
+	af_alg_data_wakeup(sk);
+	release_sock(sk);
+
+	return copied ?: err;
+}
+EXPORT_SYMBOL_GPL(af_alg_sendmsg);
+
+/**
+ * af_alg_sendpage - sendpage system call handler
+ *
+ * This is a generic implementation of sendpage to fill ctx->tsgl_list.
+ */
+ssize_t af_alg_sendpage(struct socket *sock, struct page *page,
+			int offset, size_t size, int flags)
+{
+	struct sock *sk = sock->sk;
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	struct af_alg_tsgl *sgl;
+	int err = -EINVAL;
+
+	if (flags & MSG_SENDPAGE_NOTLAST)
+		flags |= MSG_MORE;
+
+	lock_sock(sk);
+	if (!ctx->more && ctx->used)
+		goto unlock;
+
+	if (!size)
+		goto done;
+
+	if (!af_alg_writable(sk)) {
+		err = af_alg_wait_for_wmem(sk, flags);
+		if (err)
+			goto unlock;
+	}
+
+	err = af_alg_alloc_tsgl(sk);
+	if (err)
+		goto unlock;
+
+	ctx->merge = 0;
+	sgl = list_entry(ctx->tsgl_list.prev, struct af_alg_tsgl, list);
+
+	if (sgl->cur)
+		sg_unmark_end(sgl->sg + sgl->cur - 1);
+
+	sg_mark_end(sgl->sg + sgl->cur);
+
+	get_page(page);
+	sg_set_page(sgl->sg + sgl->cur, page, size, offset);
+	sgl->cur++;
+	ctx->used += size;
+
+done:
+	ctx->more = flags & MSG_MORE;
+
+unlock:
+	af_alg_data_wakeup(sk);
+	release_sock(sk);
+
+	return err ?: size;
+}
+EXPORT_SYMBOL_GPL(af_alg_sendpage);
+
+/**
+ * af_alg_async_cb - AIO callback handler
+ *
+ * This handler cleans up the struct af_alg_async_req upon completion of the
+ * AIO operation.
+ *
+ * The number of bytes to be generated with the AIO operation must be set
+ * in areq->outlen before the AIO callback handler is invoked.
+ */
+void af_alg_async_cb(struct crypto_async_request *_req, int err)
+{
+	struct af_alg_async_req *areq = _req->data;
+	struct sock *sk = areq->sk;
+	struct kiocb *iocb = areq->iocb;
+	unsigned int resultlen;
+
+	lock_sock(sk);
+
+	/* Buffer size written by crypto operation. */
+	resultlen = areq->outlen;
+
+	af_alg_free_areq_sgls(areq);
+	sock_kfree_s(sk, areq, areq->areqlen);
+	__sock_put(sk);
+
+	iocb->ki_complete(iocb, err ? err : resultlen, 0);
+
+	release_sock(sk);
+}
+EXPORT_SYMBOL_GPL(af_alg_async_cb);
+
+/**
+ * af_alg_poll - poll system call handler
+ */
+unsigned int af_alg_poll(struct file *file, struct socket *sock,
+			 poll_table *wait)
+{
+	struct sock *sk = sock->sk;
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	unsigned int mask;
+
+	sock_poll_wait(file, sk_sleep(sk), wait);
+	mask = 0;
+
+	if (!ctx->more || ctx->used)
+		mask |= POLLIN | POLLRDNORM;
+
+	if (af_alg_writable(sk))
+		mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
+
+	return mask;
+}
+EXPORT_SYMBOL_GPL(af_alg_poll);
+
+/**
+ * af_alg_alloc_areq - allocate struct af_alg_async_req
+ *
+ * @sk socket of connection to user space
+ * @areqlen size of struct af_alg_async_req + crypto_*_reqsize
+ * @return allocated data structure or ERR_PTR upon error
+ */
+struct af_alg_async_req *af_alg_alloc_areq(struct sock *sk,
+					   unsigned int areqlen)
+{
+	struct af_alg_async_req *areq = sock_kmalloc(sk, areqlen, GFP_KERNEL);
+
+	if (unlikely(!areq))
+		return ERR_PTR(-ENOMEM);
+
+	areq->areqlen = areqlen;
+	areq->sk = sk;
+	areq->last_rsgl = NULL;
+	INIT_LIST_HEAD(&areq->rsgl_list);
+	areq->tsgl = NULL;
+	areq->tsgl_entries = 0;
+
+	return areq;
+}
+EXPORT_SYMBOL_GPL(af_alg_alloc_areq);
+
+/**
+ * af_alg_get_rsgl - create the RX SGL for the output data from the crypto
+ *		     operation
+ *
+ * @sk socket of connection to user space
+ * @msg user space message
+ * @flags flags used to invoke recvmsg with
+ * @areq instance of the cryptographic request that will hold the RX SGL
+ * @maxsize maximum number of bytes to be pulled from user space
+ * @outlen number of bytes in the RX SGL
+ * @return 0 on success, < 0 upon error
+ */
+int af_alg_get_rsgl(struct sock *sk, struct msghdr *msg, int flags,
+		    struct af_alg_async_req *areq, size_t maxsize,
+		    size_t *outlen)
+{
+	struct alg_sock *ask = alg_sk(sk);
+	struct af_alg_ctx *ctx = ask->private;
+	size_t len = 0;
+
+	while (maxsize > len && msg_data_left(msg)) {
+		struct af_alg_rsgl *rsgl;
+		size_t seglen;
+		int err;
+
+		/* limit the amount of readable buffers */
+		if (!af_alg_readable(sk))
+			break;
+
+		if (!ctx->used) {
+			err = af_alg_wait_for_data(sk, flags);
+			if (err)
+				return err;
+		}
+
+		seglen = min_t(size_t, (maxsize - len),
+			       msg_data_left(msg));
+
+		if (list_empty(&areq->rsgl_list)) {
+			rsgl = &areq->first_rsgl;
+		} else {
+			rsgl = sock_kmalloc(sk, sizeof(*rsgl), GFP_KERNEL);
+			if (unlikely(!rsgl))
+				return -ENOMEM;
+		}
+
+		rsgl->sgl.npages = 0;
+		list_add_tail(&rsgl->list, &areq->rsgl_list);
+
+		/* make one iovec available as scatterlist */
+		err = af_alg_make_sg(&rsgl->sgl, &msg->msg_iter, seglen);
+		if (err < 0)
+			return err;
+
+		/* chain the new scatterlist with previous one */
+		if (areq->last_rsgl)
+			af_alg_link_sg(&areq->last_rsgl->sgl, &rsgl->sgl);
+
+		areq->last_rsgl = rsgl;
+		len += err;
+		ctx->rcvused += err;
+		rsgl->sg_num_bytes = err;
+		iov_iter_advance(&msg->msg_iter, err);
+	}
+
+	*outlen = len;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(af_alg_get_rsgl);
+
 static int __init af_alg_init(void)
 {
 	int err = proto_register(&alg_proto, 0);