[PATCH next] crypto: fix oob Read in arc4_crypt

Edward Adam Davis
2023-12-20T16:05:09Z

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