libceph: define and enforce CEPH_MAX_KEY_LEN

When decoding the key, verify that the key material would fit into
a fixed-size buffer in process_auth_done() and generally has a sane
length.

The new CEPH_MAX_KEY_LEN check replaces the existing check for a key
with no key material which is a) not universal since CEPH_CRYPTO_NONE
has to be excluded and b) doesn't provide much value since a smaller
than needed key is just as invalid as no key -- this has to be handled
elsewhere anyway.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Author: idryomov

net/ceph/crypto.c

@@ -37,9 +37,6 @@ static int set_secret(struct ceph_crypto_key *key, void *buf)
 		return -ENOTSUPP;
 	}
 
-	if (!key->len)
-		return -EINVAL;
-
 	key->key = kmemdup(buf, key->len, GFP_NOIO);
 	if (!key->key) {
 		ret = -ENOMEM;
@@ -83,6 +80,11 @@ int ceph_crypto_key_decode(struct ceph_crypto_key *key, void **p, void *end)
 	ceph_decode_copy(p, &key->created, sizeof(key->created));
 	key->len = ceph_decode_16(p);
 	ceph_decode_need(p, end, key->len, bad);
+	if (key->len > CEPH_MAX_KEY_LEN) {
+		pr_err("secret too big %d\n", key->len);
+		return -EINVAL;
+	}
+
 	ret = set_secret(key, *p);
 	memzero_explicit(*p, key->len);
 	*p += key->len;

net/ceph/crypto.h

@@ -5,7 +5,7 @@
 #include <linux/ceph/types.h>
 #include <linux/ceph/buffer.h>
 
-#define CEPH_KEY_LEN			16
+#define CEPH_MAX_KEY_LEN		16
 #define CEPH_MAX_CON_SECRET_LEN		64
 
 /*

net/ceph/messenger_v2.c

@@ -2360,7 +2360,7 @@ static int process_auth_reply_more(struct ceph_connection *con,
  */
 static int process_auth_done(struct ceph_connection *con, void *p, void *end)
 {
-	u8 session_key_buf[CEPH_KEY_LEN + 16];
+	u8 session_key_buf[CEPH_MAX_KEY_LEN + 16];
 	u8 con_secret_buf[CEPH_MAX_CON_SECRET_LEN + 16];
 	u8 *session_key = PTR_ALIGN(&session_key_buf[0], 16);
 	u8 *con_secret = PTR_ALIGN(&con_secret_buf[0], 16);