linux-kernel - [PATCH v2] crypto: algif_skcipher - Require setkey before accept(2)

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Date:	Fri, 25 Dec 2015 15:40:05 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	syzkaller@...glegroups.com, davem@...emloft.net,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	kcc@...gle.com, glider@...gle.com, edumazet@...gle.com,
	sasha.levin@...cle.com, keescook@...gle.com
Subject: [PATCH v2] crypto: algif_skcipher - Require setkey before accept(2)

Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> I am testing with your two patches:
> crypto: algif_skcipher - Use new skcipher interface
> crypto: algif_skcipher - Require setkey before accept(2)
> on top of a88164345b81292b55a8d4829fdd35c8d611cd7d (Dec 23).

You sent the email to everyone on the original CC list except me.
Please don't do that.

> Now the following program causes a bunch of use-after-frees and them
> kills kernel:

Yes there is an obvious bug in the patch that Julia Lawall has
responded to in another thread.  Here is a fixed version.

---8<--
Some cipher implementations will crash if you try to use them
without calling setkey first.  This patch adds a check so that
the accept(2) call will fail with -ENOKEY if setkey hasn't been
done on the socket yet.

Cc: stable@...r.kernel.org
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index 5c756b3..f4431bc 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -31,6 +31,11 @@ struct skcipher_sg_list {
 	struct scatterlist sg[0];
 };
 
+struct skcipher_tfm {
+	struct crypto_skcipher *skcipher;
+	bool has_key;
+};
+
 struct skcipher_ctx {
 	struct list_head tsgl;
 	struct af_alg_sgl rsgl;
@@ -750,17 +755,41 @@ static struct proto_ops algif_skcipher_ops = {
 
 static void *skcipher_bind(const char *name, u32 type, u32 mask)
 {
-	return crypto_alloc_skcipher(name, type, mask);
+	struct skcipher_tfm *tfm;
+	struct crypto_skcipher *skcipher;
+
+	tfm = kzalloc(sizeof(*tfm), GFP_KERNEL);
+	if (!tfm)
+		return ERR_PTR(-ENOMEM);
+
+	skcipher = crypto_alloc_skcipher(name, type, mask);
+	if (IS_ERR(skcipher)) {
+		kfree(tfm);
+		return ERR_CAST(skcipher);
+	}
+
+	tfm->skcipher = skcipher;
+
+	return tfm;
 }
 
 static void skcipher_release(void *private)
 {
-	crypto_free_skcipher(private);
+	struct skcipher_tfm *tfm = private;
+
+	crypto_free_skcipher(tfm->skcipher);
+	kfree(tfm);
 }
 
 static int skcipher_setkey(void *private, const u8 *key, unsigned int keylen)
 {
-	return crypto_skcipher_setkey(private, key, keylen);
+	struct skcipher_tfm *tfm = private;
+	int err;
+
+	err = crypto_skcipher_setkey(tfm->skcipher, key, keylen);
+	tfm->has_key = !err;
+
+	return err;
 }
 
 static void skcipher_wait(struct sock *sk)
@@ -792,20 +821,25 @@ static int skcipher_accept_parent(void *private, struct sock *sk)
 {
 	struct skcipher_ctx *ctx;
 	struct alg_sock *ask = alg_sk(sk);
-	unsigned int len = sizeof(*ctx) + crypto_skcipher_reqsize(private);
+	struct skcipher_tfm *tfm = private;
+	struct crypto_skcipher *skcipher = tfm->skcipher;
+	unsigned int len = sizeof(*ctx) + crypto_skcipher_reqsize(skcipher);
+
+	if (!tfm->has_key)
+		return -ENOKEY;
 
 	ctx = sock_kmalloc(sk, len, GFP_KERNEL);
 	if (!ctx)
 		return -ENOMEM;
 
-	ctx->iv = sock_kmalloc(sk, crypto_skcipher_ivsize(private),
+	ctx->iv = sock_kmalloc(sk, crypto_skcipher_ivsize(skcipher),
 			       GFP_KERNEL);
 	if (!ctx->iv) {
 		sock_kfree_s(sk, ctx, len);
 		return -ENOMEM;
 	}
 
-	memset(ctx->iv, 0, crypto_skcipher_ivsize(private));
+	memset(ctx->iv, 0, crypto_skcipher_ivsize(skcipher));
 
 	INIT_LIST_HEAD(&ctx->tsgl);
 	ctx->len = len;
@@ -818,7 +852,7 @@ static int skcipher_accept_parent(void *private, struct sock *sk)
 
 	ask->private = ctx;
 
-	skcipher_request_set_tfm(&ctx->req, private);
+	skcipher_request_set_tfm(&ctx->req, skcipher);
 	skcipher_request_set_callback(&ctx->req, CRYPTO_TFM_REQ_MAY_BACKLOG,
 				      af_alg_complete, &ctx->completion);
 
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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