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>

1 files changed, 19 insertions, 13 deletions

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 6da7aebde8df..98f03b143b38 100644
--- 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;