The kernel crypto API AEAD cipher operation generates output such that
space for the AAD is reserved in the output buffer without being
touched. The processed ciphertext/plaintext is appended to the reserved
AAD buffer.
The user space interface followed that approach. However, this is a
violation of the POSIX read definition which requires that any read data
is placed at the beginning of the caller-provided buffer. As the kernel
crypto API would leave room for the AAD, the old approach did not fully
comply with the POSIX specification.
The patch changes the user space AF_ALG AEAD interface such that the
processed ciphertext/plaintext are now placed at the beginning of the
user buffer provided with the read system call. That means the user
space interface now deviates from the in-kernel output buffer handling.
For the cipher operation, the AAD buffer provided during input is
pointed to by a new SGL which is chained with the output buffer SGL.
With this approach, only pointers to one copy of the AAD are maintained
to avoid data duplication.
With this solution, the caller must not use sendpage with the exact same
buffers for input and output. The following rationale applies: When
the caller sends the same buffer for input/output to the sendpage
operation, the cipher operation now will write the ciphertext to the
beginning of the buffer where the AAD used to be. The subsequent tag
calculation will now use the data it finds where the AAD is expected.
As the cipher operation has already replaced the AAD with the ciphertext,
the tag calculation will take the ciphertext as AAD and thus calculate
a wrong tag.
Reported-by: Mat Martineau <mathew.j.martin...@linux.intel.com>
Signed-off-by: Stephan Mueller <smuel...@chronox.de>
---
crypto/algif_aead.c | 143 +++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 113 insertions(+), 30 deletions(-)
diff --git a/crypto/algif_aead.c b/crypto/algif_aead.c
index c54bcb8..0212cc2 100644
--- a/crypto/algif_aead.c
+++ b/crypto/algif_aead.c
@@ -32,6 +32,7 @@ struct aead_sg_list {
struct aead_async_rsgl {
struct af_alg_sgl sgl;
struct list_head list;
+ bool new_page;
};
struct aead_async_req {
@@ -405,6 +406,61 @@ static void aead_async_cb(struct crypto_async_request
*_req, int err)
iocb->ki_complete(iocb, err, err);
}
+/**
+ * scatterwalk_get_part() - get subset a scatterlist
+ *
+ * @dst: destination SGL to receive the pointers from source SGL
+ * @src: source SGL
+ * @len: data length in bytes to get from source SGL
+ * @max_sgs: number of SGs present in dst SGL to prevent overstepping
boundaries
+ *
+ * @return: number of SG entries in dst
+ */
+static inline int scatterwalk_get_part(struct scatterlist *dst,
+ struct scatterlist *src,
+ unsigned int len, unsigned int max_sgs)
+{
+ /* leave one SG entry for chaining */
+ unsigned int j = 1;
+
+ while (len && j < max_sgs) {
+ unsigned int todo = min_t(unsigned int, len, src->length);
+
+ sg_set_page(dst, sg_page(src), todo, src->offset);
+ if (src->length >= len) {
+ sg_mark_end(dst);
+ break;
+ }
+ len -= todo;
+ j++;
+ src = sg_next(src);
+ dst = sg_next(dst);
+ }
+
+ return j;
+}
+
+static inline int aead_alloc_rsgl(struct sock *sk, struct aead_async_rsgl
**ret)
+{
+ struct aead_async_rsgl *rsgl =
+ sock_kmalloc(sk, sizeof(*rsgl), GFP_KERNEL);
+ if (unlikely(!rsgl))
+ return -ENOMEM;
+ *ret = rsgl;
+ return 0;
+}
+
+static inline int aead_get_rsgl_areq(struct sock *sk,
+ struct aead_async_req *areq,
+ struct aead_async_rsgl **ret)
+{
+ if (list_empty(&areq->list)) {
+ *ret = &areq->first_rsgl;
+ return 0;
+ } else
+ return aead_alloc_rsgl(sk, ret);
+}
+
static int aead_recvmsg_async(struct socket *sock, struct msghdr *msg,
int flags)
{
@@ -433,7 +489,7 @@ static int aead_recvmsg_async(struct socket *sock, struct
msghdr *msg,
if (!aead_sufficient_data(ctx))
goto unlock;
- used = ctx->used;
+ used = ctx->used - ctx->aead_assoclen;
if (ctx->enc)
outlen = used + as;
else
@@ -452,7 +508,6 @@ static int aead_recvmsg_async(struct socket *sock, struct
msghdr *msg,
aead_request_set_ad(req, ctx->aead_assoclen);
aead_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
aead_async_cb, sk);
- used -= ctx->aead_assoclen;
/* take over all tx sgls from ctx */
areq->tsgl = sock_kmalloc(sk, sizeof(*areq->tsgl) * sgl->cur,
@@ -467,21 +522,26 @@ static int aead_recvmsg_async(struct socket *sock, struct
msghdr *msg,
areq->tsgls = sgl->cur;
+ /* set AAD buffer */
+ err = aead_get_rsgl_areq(sk, areq, &rsgl);
+ if (err)
+ goto free;
+ list_add_tail(&rsgl->list, &areq->list);
+ sg_init_table(rsgl->sgl.sg, ALG_MAX_PAGES);
+ rsgl->sgl.npages = scatterwalk_get_part(rsgl->sgl.sg, sgl->sg,
+ ctx->aead_assoclen,
+ ALG_MAX_PAGES);
+ rsgl->new_page = false;
+ last_rsgl = rsgl;
+
/* create rx sgls */
while (outlen > usedpages && iov_iter_count(&msg->msg_iter)) {
size_t seglen = min_t(size_t, iov_iter_count(&msg->msg_iter),
(outlen - usedpages));
- if (list_empty(&areq->list)) {
- rsgl = &areq->first_rsgl;
-
- } else {
- rsgl = sock_kmalloc(sk, sizeof(*rsgl), GFP_KERNEL);
- if (unlikely(!rsgl)) {
- err = -ENOMEM;
- goto free;
- }
- }
+ err = aead_get_rsgl_areq(sk, areq, &rsgl);
+ if (err)
+ goto free;
rsgl->sgl.npages = 0;
list_add_tail(&rsgl->list, &areq->list);
@@ -491,6 +551,7 @@ static int aead_recvmsg_async(struct socket *sock, struct
msghdr *msg,
goto free;
usedpages += err;
+ rsgl->new_page = true;
/* chain the new scatterlist with previous one */
if (last_rsgl)
@@ -507,7 +568,7 @@ static int aead_recvmsg_async(struct socket *sock, struct
msghdr *msg,
if (used < less) {
err = -EINVAL;
- goto unlock;
+ goto free;
}
used -= less;
outlen -= less;
@@ -531,7 +592,8 @@ static int aead_recvmsg_async(struct socket *sock, struct
msghdr *msg,
free:
list_for_each_entry(rsgl, &areq->list, list) {
- af_alg_free_sg(&rsgl->sgl);
+ if (rsgl->new_page)
+ af_alg_free_sg(&rsgl->sgl);
if (rsgl != &areq->first_rsgl)
sock_kfree_s(sk, rsgl, sizeof(*rsgl));
}
@@ -545,6 +607,16 @@ static int aead_recvmsg_async(struct socket *sock, struct
msghdr *msg,
return err ? err : outlen;
}
+static inline int aead_get_rsgl_ctx(struct sock *sk, struct aead_ctx *ctx,
+ struct aead_async_rsgl **ret)
+{
+ if (list_empty(&ctx->list)) {
+ *ret = &ctx->first_rsgl;
+ return 0;
+ } else
+ return aead_alloc_rsgl(sk, ret);
+}
+
static int aead_recvmsg_sync(struct socket *sock, struct msghdr *msg, int
flags)
{
struct sock *sk = sock->sk;
@@ -582,9 +654,6 @@ static int aead_recvmsg_sync(struct socket *sock, struct
msghdr *msg, int flags)
goto unlock;
}
- /* data length provided by caller via sendmsg/sendpage */
- used = ctx->used;
-
/*
* Make sure sufficient data is present -- note, the same check is
* is also present in sendmsg/sendpage. The checks in sendpage/sendmsg
@@ -598,6 +667,12 @@ static int aead_recvmsg_sync(struct socket *sock, struct
msghdr *msg, int flags)
goto unlock;
/*
+ * The cipher operation input data is reduced by the associated data
+ * as the destination buffer will not hold the AAD.
+ */
+ used = ctx->used - ctx->aead_assoclen;
+
+ /*
* Calculate the minimum output buffer size holding the result of the
* cipher operation. When encrypting data, the receiving buffer is
* larger by the tag length compared to the input buffer as the
@@ -611,25 +686,29 @@ static int aead_recvmsg_sync(struct socket *sock, struct
msghdr *msg, int flags)
outlen = used - as;
/*
- * The cipher operation input data is reduced by the associated data
- * length as this data is processed separately later on.
+ * Pre-pend the AAD buffer from the source SGL to the destination SGL.
+ * As the AAD buffer is not touched by the AEAD operation, the source
+ * SG buffers remain unchanged.
*/
- used -= ctx->aead_assoclen;
+ err = aead_get_rsgl_ctx(sk, ctx, &rsgl);
+ if (err)
+ goto unlock;
+ list_add_tail(&rsgl->list, &ctx->list);
+ sg_init_table(rsgl->sgl.sg, ALG_MAX_PAGES);
+ rsgl->sgl.npages = scatterwalk_get_part(rsgl->sgl.sg, sgl->sg,
+ ctx->aead_assoclen,
+ ALG_MAX_PAGES);
+ rsgl->new_page = false;
+ last_rsgl = rsgl;
/* convert iovecs of output buffers into scatterlists */
while (outlen > usedpages && iov_iter_count(&msg->msg_iter)) {
size_t seglen = min_t(size_t, iov_iter_count(&msg->msg_iter),
(outlen - usedpages));
- if (list_empty(&ctx->list)) {
- rsgl = &ctx->first_rsgl;
- } else {
- rsgl = sock_kmalloc(sk, sizeof(*rsgl), GFP_KERNEL);
- if (unlikely(!rsgl)) {
- err = -ENOMEM;
- goto unlock;
- }
- }
+ err = aead_get_rsgl_ctx(sk, ctx, &rsgl);
+ if (err)
+ goto unlock;
rsgl->sgl.npages = 0;
list_add_tail(&rsgl->list, &ctx->list);
@@ -637,7 +716,10 @@ static int aead_recvmsg_sync(struct socket *sock, struct
msghdr *msg, int flags)
err = af_alg_make_sg(&rsgl->sgl, &msg->msg_iter, seglen);
if (err < 0)
goto unlock;
+
usedpages += err;
+ rsgl->new_page = true;
+
/* chain the new scatterlist with previous one */
if (last_rsgl)
af_alg_link_sg(&last_rsgl->sgl, &rsgl->sgl);
@@ -688,7 +770,8 @@ static int aead_recvmsg_sync(struct socket *sock, struct
msghdr *msg, int flags)
unlock:
list_for_each_entry_safe(rsgl, tmp, &ctx->list, list) {
- af_alg_free_sg(&rsgl->sgl);
+ if (rsgl->new_page)
+ af_alg_free_sg(&rsgl->sgl);
if (rsgl != &ctx->first_rsgl)
sock_kfree_s(sk, rsgl, sizeof(*rsgl));
list_del(&rsgl->list);
--
2.7.4
--
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