rxrpc: Randomise epoch and starting client conn ID values

Create a random epoch value rather than a time-based one on startup and set
the top bit to indicate that this is the case.

Also create a random starting client connection ID value.  This will be
incremented from here as new client connections are created.

Signed-off-by: David Howells <dhowells@redhat.com>

2 files changed, 9 insertions, 1 deletions

diff --git a/include/rxrpc/packet.h b/include/rxrpc/packet.h
index b2017440b765..3c6128e1fdbe 100644
--- a/include/rxrpc/packet.h
+++ b/include/rxrpc/packet.h
@@ -24,6 +24,7 @@ typedef __be32	rxrpc_serial_net_t; /* on-the-wire Rx message serial number */
  */
 struct rxrpc_wire_header {
         __be32          epoch;          /* client boot timestamp */
+#define RXRPC_RANDOM_EPOCH      0x80000000      /* Random if set, date-based if not */
 
         __be32          cid;            /* connection and channel ID */
 #define RXRPC_MAXCALLS          4                       /* max active calls per conn */
diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
index 32d544995dda..b66a9e6f8d04 100644
--- a/net/rxrpc/af_rxrpc.c
+++ b/net/rxrpc/af_rxrpc.c
@@ -16,6 +16,7 @@
 #include <linux/net.h>
 #include <linux/slab.h>
 #include <linux/skbuff.h>
+#include <linux/random.h>
 #include <linux/poll.h>
 #include <linux/proc_fs.h>
 #include <linux/key-type.h>
@@ -700,7 +701,13 @@ static int __init af_rxrpc_init(void)
 
         BUILD_BUG_ON(sizeof(struct rxrpc_skb_priv) > FIELD_SIZEOF(struct sk_buff, cb));
 
-        rxrpc_epoch = get_seconds();
+        get_random_bytes(&rxrpc_epoch, sizeof(rxrpc_epoch));
+        rxrpc_epoch |= RXRPC_RANDOM_EPOCH;
+        get_random_bytes(&rxrpc_client_conn_ids.cur,
+                         sizeof(rxrpc_client_conn_ids.cur));
+        rxrpc_client_conn_ids.cur &= 0x3fffffff;
+        if (rxrpc_client_conn_ids.cur == 0)
+                rxrpc_client_conn_ids.cur = 1;
 
         ret = -ENOMEM;
         rxrpc_call_jar = kmem_cache_create(