[PATCH next] crypto: fix oob Read in arc4_crypt

[Edward Adam Davis <eadavis@qq.com>]

The space allocated to areq is not sufficient to access the member __ctx of 
struct skcipher_request, as the space occupied by struct arc4_ctx for reading 
is 1032 bytes, while the requested memory size in skcipher_recvmsg() is:
sizeof(struct af_alg_async_req) + crypto_skcipher_reqsize(tfm) = 736 bytes,
which does not include the memory required for __ctx of struct skcipher_request.

Reported-by: syzbot+8ffb0839a24e9c6bfa76@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 crypto/algif_skcipher.c            | 10 +++++++---
 crypto/skcipher.c                  |  1 -
 include/crypto/internal/skcipher.h |  1 +
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index 02cea2149504..b69d361b5515 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -33,6 +33,7 @@
 #include <linux/module.h>
 #include <linux/net.h>
 #include <net/sock.h>
+#include <crypto/internal/skcipher.h>
 
 static int skcipher_sendmsg(struct socket *sock, struct msghdr *msg,
 			    size_t size)
@@ -102,11 +103,12 @@ static int _skcipher_recvmsg(struct socket *sock, struct msghdr *msg,
 	struct alg_sock *pask = alg_sk(psk);
 	struct af_alg_ctx *ctx = ask->private;
 	struct crypto_skcipher *tfm = pask->private;
+	struct skcipher_alg *alg = crypto_skcipher_alg(tfm);
 	unsigned int bs = crypto_skcipher_chunksize(tfm);
 	struct af_alg_async_req *areq;
 	unsigned cflags = 0;
 	int err = 0;
-	size_t len = 0;
+	size_t len = 0, aqlen;
 
 	if (!ctx->init || (ctx->more && ctx->used < bs)) {
 		err = af_alg_wait_for_data(sk, flags, bs);
@@ -115,8 +117,10 @@ static int _skcipher_recvmsg(struct socket *sock, struct msghdr *msg,
 	}
 
 	/* Allocate cipher request for current operation. */
-	areq = af_alg_alloc_areq(sk, sizeof(struct af_alg_async_req) +
-				     crypto_skcipher_reqsize(tfm));
+	aqlen = sizeof(struct af_alg_async_req) + crypto_skcipher_reqsize(tfm);
+	if (alg->co.base.cra_type != &crypto_skcipher_type)
+		aqlen += 1032;
+	areq = af_alg_alloc_areq(sk, aqlen);
 	if (IS_ERR(areq))
 		return PTR_ERR(areq);
 
diff --git a/crypto/skcipher.c b/crypto/skcipher.c
index bc70e159d27d..0ae4a05a5aa7 100644
--- a/crypto/skcipher.c
+++ b/crypto/skcipher.c
@@ -44,7 +44,6 @@ struct skcipher_walk_buffer {
 	u8 buffer[];
 };
 
-static const struct crypto_type crypto_skcipher_type;
 
 static int skcipher_walk_next(struct skcipher_walk *walk);
 
diff --git a/include/crypto/internal/skcipher.h b/include/crypto/internal/skcipher.h
index 7ae42afdcf3e..3c05872652f2 100644
--- a/include/crypto/internal/skcipher.h
+++ b/include/crypto/internal/skcipher.h
@@ -24,6 +24,7 @@
 
 struct aead_request;
 struct rtattr;
+static const struct crypto_type crypto_skcipher_type;
 
 struct skcipher_instance {
 	void (*free)(struct skcipher_instance *inst);
-- 
2.43.0