libceph: align session_key and con_secret to 16 bytes

crypto_shash_setkey() and crypto_aead_setkey() will do a (small)
GFP_ATOMIC allocation to align the key if it isn't suitably aligned.
It's not a big deal, but at the same time easy to avoid.

The actual alignment requirement is dynamic, queryable with
crypto_shash_alignmask() and crypto_aead_alignmask(), but shouldn't
be stricter than 16 bytes for our algorithms.

Fixes: cd1a677 ("libceph, ceph: implement msgr2.1 protocol (crc and secure modes)")
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

net/ceph/messenger_v2.c

@@ -2033,10 +2033,18 @@ static int process_auth_reply_more(struct ceph_connection *con,
 	return -EINVAL;
 }
 
+/*
+ * Align session_key and con_secret to avoid GFP_ATOMIC allocation
+ * inside crypto_shash_setkey() and crypto_aead_setkey() called from
+ * setup_crypto().  __aligned(16) isn't guaranteed to work for stack
+ * objects, so do it by hand.
+ */
 static int process_auth_done(struct ceph_connection *con, void *p, void *end)
 {
-	u8 session_key[CEPH_KEY_LEN];
-	u8 con_secret[CEPH_MAX_CON_SECRET_LEN];
+	u8 session_key_buf[CEPH_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);
 	int session_key_len, con_secret_len;
 	int payload_len;
 	u64 global_id;