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        syzbot+13a08c0bf4d212766c3c@syzkaller.appspotmail.com,
        syzbot+14234ccf6d0ef629ec1a@syzkaller.appspotmail.com,
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        syzbot+472626bb5e7c59fb768f@syzkaller.appspotmail.com,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Matthew Wilcox <willy@infradead.org>,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH net-next] crypto: af_alg/hash: Fix recvmsg() after sendmsg(MSG_MORE)
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From:   David Howells <dhowells@redhat.com>
Date:   Thu, 15 Jun 2023 00:27:53 +0100
Message-ID: <1679829.1686785273@warthog.procyon.org.uk>
Precedence: bulk

    =

If an AF_ALG socket bound to a hashing algorithm is sent a zero-length
message with MSG_MORE set and then recvmsg() is called without first
sending another message without MSG_MORE set to end the operation, an oops
will occur because the crypto context and result doesn't now get set up in
advance because hash_sendmsg() now defers that as long as possible in the
hope that it can use crypto_ahash_digest() - and then because the message
is zero-length, it the data wrangling loop is skipped.

Fix this by always making a pass of the loop, even in the case that no dat=
a
is provided to the sendmsg().

Fix also extract_iter_to_sg() to handle a zero-length iterator by returnin=
g
0 immediately.

Whilst we're at it, remove the code to create a kvmalloc'd scatterlist if
we get more than ALG_MAX_PAGES - this shouldn't happen.

Fixes: c662b043cdca ("crypto: af_alg/hash: Support MSG_SPLICE_PAGES")
Reported-by: syzbot+13a08c0bf4d212766c3c@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000b928f705fdeb873a@google.com/
Reported-by: syzbot+14234ccf6d0ef629ec1a@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000c047db05fdeb8790@google.com/
Reported-by: syzbot+4e2e47f32607d0f72d43@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000bcca3205fdeb87fb@google.com/
Reported-by: syzbot+472626bb5e7c59fb768f@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000b55d8805fdeb8385@google.com/
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: syzbot+13a08c0bf4d212766c3c@syzkaller.appspotmail.com
Tested-by: syzbot+14234ccf6d0ef629ec1a@syzkaller.appspotmail.com
Tested-by: syzbot+4e2e47f32607d0f72d43@syzkaller.appspotmail.com
Tested-by: syzbot+472626bb5e7c59fb768f@syzkaller.appspotmail.com
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-crypto@vger.kernel.org
cc: netdev@vger.kernel.org
---
 crypto/algif_hash.c |   21 +++++----------------
 lib/scatterlist.c   |    2 +-
 2 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
index dfb048cefb60..1176533a55c9 100644
--- a/crypto/algif_hash.c
+++ b/crypto/algif_hash.c
@@ -83,26 +83,14 @@ static int hash_sendmsg(struct socket *sock, struct ms=
ghdr *msg,
 =

 	ctx->more =3D false;
 =

-	while (msg_data_left(msg)) {
+	do {
 		ctx->sgl.sgt.sgl =3D ctx->sgl.sgl;
 		ctx->sgl.sgt.nents =3D 0;
 		ctx->sgl.sgt.orig_nents =3D 0;
 =

 		err =3D -EIO;
 		npages =3D iov_iter_npages(&msg->msg_iter, max_pages);
-		if (npages =3D=3D 0)
-			goto unlock_free;
-
-		if (npages > ARRAY_SIZE(ctx->sgl.sgl)) {
-			err =3D -ENOMEM;
-			ctx->sgl.sgt.sgl =3D
-				kvmalloc(array_size(npages,
-						    sizeof(*ctx->sgl.sgt.sgl)),
-					 GFP_KERNEL);
-			if (!ctx->sgl.sgt.sgl)
-				goto unlock_free;
-		}
-		sg_init_table(ctx->sgl.sgl, npages);
+		sg_init_table(ctx->sgl.sgl, max_t(size_t, npages, 1));
 =

 		ctx->sgl.need_unpin =3D iov_iter_extract_will_pin(&msg->msg_iter);
 =

@@ -111,7 +99,8 @@ static int hash_sendmsg(struct socket *sock, struct msg=
hdr *msg,
 		if (err < 0)
 			goto unlock_free;
 		len =3D err;
-		sg_mark_end(ctx->sgl.sgt.sgl + ctx->sgl.sgt.nents - 1);
+		if (len > 0)
+			sg_mark_end(ctx->sgl.sgt.sgl + ctx->sgl.sgt.nents - 1);
 =

 		if (!msg_data_left(msg)) {
 			err =3D hash_alloc_result(sk, ctx);
@@ -148,7 +137,7 @@ static int hash_sendmsg(struct socket *sock, struct ms=
ghdr *msg,
 =

 		copied +=3D len;
 		af_alg_free_sg(&ctx->sgl);
-	}
+	} while (msg_data_left(msg));
 =

 	ctx->more =3D msg->msg_flags & MSG_MORE;
 	err =3D 0;
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index e97d7060329e..77a7b18ee751 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -1340,7 +1340,7 @@ ssize_t extract_iter_to_sg(struct iov_iter *iter, si=
ze_t maxsize,
 			   struct sg_table *sgtable, unsigned int sg_max,
 			   iov_iter_extraction_t extraction_flags)
 {
-	if (maxsize =3D=3D 0)
+	if (!maxsize || !iter->count)
 		return 0;
 =

 	switch (iov_iter_type(iter)) {