drbd: Wrong use of RCU in receive_protocol()

It is not enough to grab net_conf->integrity_alg under rcu_read_lock()
and access it outside of it; the entire net_conf object may be gone by
then.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 6da7aeb..98f03b1 100644 (file)
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -2998,7 +2998,6 @@ static int receive_protocol(struct drbd_tconn *tconn, struct packet_info *pi)
        int p_proto, p_after_sb_0p, p_after_sb_1p, p_after_sb_2p;
        int p_want_lose, p_two_primaries, cf;
        char p_integrity_alg[SHARED_SECRET_MAX] = "";
-       unsigned char *my_alg;
        struct net_conf *nc;
 
        p_proto         = be32_to_cpu(p->protocol);
@@ -3009,6 +3008,18 @@ static int receive_protocol(struct drbd_tconn *tconn, struct packet_info *pi)
        cf              = be32_to_cpu(p->conn_flags);
        p_want_lose = cf & CF_WANT_LOSE;
 
+       if (tconn->agreed_pro_version >= 87) {
+               int err;
+
+               if (pi->size > sizeof(p_integrity_alg))
+                       return -EIO;
+               err = drbd_recv_all(tconn, p_integrity_alg, pi->size);
+               if (err)
+                       return err;
+
+               p_integrity_alg[SHARED_SECRET_MAX-1] = 0;
+       }
+
        clear_bit(CONN_DRY_RUN, &tconn->flags);
 
        if (cf & CF_DRY_RUN)
@@ -3047,23 +3058,18 @@ static int receive_protocol(struct drbd_tconn *tconn, struct packet_info *pi)
                goto disconnect_rcu_unlock;
        }
 
-       my_alg = nc->integrity_alg;
-       rcu_read_unlock();
-
        if (tconn->agreed_pro_version >= 87) {
-               int err;
-
-               err = drbd_recv_all(tconn, p_integrity_alg, pi->size);
-               if (err)
-                       return err;
-
-               p_integrity_alg[SHARED_SECRET_MAX-1] = 0;
-               if (strcmp(p_integrity_alg, my_alg)) {
+               if (strcmp(p_integrity_alg, nc->integrity_alg)) {
                        conn_err(tconn, "incompatible setting of the data-integrity-alg\n");
                        goto disconnect;
                }
+       }
+
+       rcu_read_unlock();
+
+       if (tconn->agreed_pro_version >= 87) {
                conn_info(tconn, "data-integrity-alg: %s\n",
-                    my_alg[0] ? my_alg : (unsigned char *)"<not-used>");
+                         nc->integrity_alg[0] ? nc->integrity_alg : (unsigned char *)"<not-used>");
        }
 
        return 0;