crypto: hash - prevent using keyed hashes without setting key

Currently, almost none of the keyed hash algorithms check whether a key
has been set before proceeding.  Some algorithms are okay with this and
will effectively just use a key of all 0's or some other bogus default.
However, others will severely break, as demonstrated using
"hmac(sha3-512-generic)", the unkeyed use of which causes a kernel crash
via a (potentially exploitable) stack buffer overflow.

A while ago, this problem was solved for AF_ALG by pairing each hash
transform with a 'has_key' bool.  However, there are still other places
in the kernel where userspace can specify an arbitrary hash algorithm by
name, and the kernel uses it as unkeyed hash without checking whether it
is really unkeyed.  Examples of this include:

    - KEYCTL_DH_COMPUTE, via the KDF extension
    - dm-verity
    - dm-crypt, via the ESSIV support
    - dm-integrity, via the "internal hash" mode with no key given
    - drbd (Distributed Replicated Block Device)

This bug is especially bad for KEYCTL_DH_COMPUTE as that requires no
privileges to call.

Fix the bug for all users by adding a flag CRYPTO_TFM_NEED_KEY to the
->crt_flags of each hash transform that indicates whether the transform
still needs to be keyed or not.  Then, make the hash init, import, and
digest functions return -ENOKEY if the key is still needed.

The new flag also replaces the 'has_key' bool which algif_hash was
previously using, thereby simplifying the algif_hash implementation.

Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 11 insertions, 41 deletions

diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
index 76d2e716c792..6c9b1927a520 100644
--- a/crypto/algif_hash.c
+++ b/crypto/algif_hash.c
@@ -34,11 +34,6 @@ struct hash_ctx {
 	struct ahash_request req;
 };
 
-struct algif_hash_tfm {
-	struct crypto_ahash *hash;
-	bool has_key;
-};
-
 static int hash_alloc_result(struct sock *sk, struct hash_ctx *ctx)
 {
 	unsigned ds;
@@ -307,7 +302,7 @@ static int hash_check_key(struct socket *sock)
 	int err = 0;
 	struct sock *psk;
 	struct alg_sock *pask;
-	struct algif_hash_tfm *tfm;
+	struct crypto_ahash *tfm;
 	struct sock *sk = sock->sk;
 	struct alg_sock *ask = alg_sk(sk);
 
@@ -321,7 +316,7 @@ static int hash_check_key(struct socket *sock)
 
 	err = -ENOKEY;
 	lock_sock_nested(psk, SINGLE_DEPTH_NESTING);
-	if (!tfm->has_key)
+	if (crypto_ahash_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)
 		goto unlock;
 
 	if (!pask->refcnt++)
@@ -412,41 +407,17 @@ static struct proto_ops algif_hash_ops_nokey = {
 
 static void *hash_bind(const char *name, u32 type, u32 mask)
 {
-	struct algif_hash_tfm *tfm;
-	struct crypto_ahash *hash;
-
-	tfm = kzalloc(sizeof(*tfm), GFP_KERNEL);
-	if (!tfm)
-		return ERR_PTR(-ENOMEM);
-
-	hash = crypto_alloc_ahash(name, type, mask);
-	if (IS_ERR(hash)) {
-		kfree(tfm);
-		return ERR_CAST(hash);
-	}
-
-	tfm->hash = hash;
-
-	return tfm;
+	return crypto_alloc_ahash(name, type, mask);
 }
 
 static void hash_release(void *private)
 {
-	struct algif_hash_tfm *tfm = private;
-
-	crypto_free_ahash(tfm->hash);
-	kfree(tfm);
+	crypto_free_ahash(private);
 }
 
 static int hash_setkey(void *private, const u8 *key, unsigned int keylen)
 {
-	struct algif_hash_tfm *tfm = private;
-	int err;
-
-	err = crypto_ahash_setkey(tfm->hash, key, keylen);
-	tfm->has_key = !err;
-
-	return err;
+	return crypto_ahash_setkey(private, key, keylen);
 }
 
 static void hash_sock_destruct(struct sock *sk)
@@ -461,11 +432,10 @@ static void hash_sock_destruct(struct sock *sk)
 
 static int hash_accept_parent_nokey(void *private, struct sock *sk)
 {
-	struct hash_ctx *ctx;
+	struct crypto_ahash *tfm = private;
 	struct alg_sock *ask = alg_sk(sk);
-	struct algif_hash_tfm *tfm = private;
-	struct crypto_ahash *hash = tfm->hash;
-	unsigned len = sizeof(*ctx) + crypto_ahash_reqsize(hash);
+	struct hash_ctx *ctx;
+	unsigned int len = sizeof(*ctx) + crypto_ahash_reqsize(tfm);
 
 	ctx = sock_kmalloc(sk, len, GFP_KERNEL);
 	if (!ctx)
@@ -478,7 +448,7 @@ static int hash_accept_parent_nokey(void *private, struct sock *sk)
 
 	ask->private = ctx;
 
-	ahash_request_set_tfm(&ctx->req, hash);
+	ahash_request_set_tfm(&ctx->req, tfm);
 	ahash_request_set_callback(&ctx->req, CRYPTO_TFM_REQ_MAY_BACKLOG,
 				   crypto_req_done, &ctx->wait);
 
@@ -489,9 +459,9 @@ static int hash_accept_parent_nokey(void *private, struct sock *sk)
 
 static int hash_accept_parent(void *private, struct sock *sk)
 {
-	struct algif_hash_tfm *tfm = private;
+	struct crypto_ahash *tfm = private;
 
-	if (!tfm->has_key && crypto_ahash_has_setkey(tfm->hash))
+	if (crypto_ahash_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)
 		return -ENOKEY;
 
 	return hash_accept_parent_nokey(private, sk);