can: should not use __dev_get_by_index() without locks

bcm_proc_getifname() is called with RTNL and dev_base_lock
not held. It calls __dev_get_by_index() without locks, and
this is illegal (might crash)

Close the race by holding dev_base_lock and copying dev->name
in the protected section.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 7 deletions

diff --git a/net/can/bcm.c b/net/can/bcm.c
index 597da4f8f888..e8d58f33fe09 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -132,23 +132,27 @@ static inline struct bcm_sock *bcm_sk(const struct sock *sk)
 /*
  * procfs functions
  */
-static char *bcm_proc_getifname(int ifindex)
+static char *bcm_proc_getifname(char *result, int ifindex)
 {
         struct net_device *dev;
 
         if (!ifindex)
                 return "any";
 
-        /* no usage counting */
+        read_lock(&dev_base_lock);
         dev = __dev_get_by_index(&init_net, ifindex);
         if (dev)
-                return dev->name;
+                strcpy(result, dev->name);
+        else
+                strcpy(result, "???");
+        read_unlock(&dev_base_lock);
 
-        return "???";
+        return result;
 }
 
 static int bcm_proc_show(struct seq_file *m, void *v)
 {
+        char ifname[IFNAMSIZ];
         struct sock *sk = (struct sock *)m->private;
         struct bcm_sock *bo = bcm_sk(sk);
         struct bcm_op *op;
@@ -157,7 +161,7 @@ static int bcm_proc_show(struct seq_file *m, void *v)
         seq_printf(m, " / sk %p", sk);
         seq_printf(m, " / bo %p", bo);
         seq_printf(m, " / dropped %lu", bo->dropped_usr_msgs);
-        seq_printf(m, " / bound %s", bcm_proc_getifname(bo->ifindex));
+        seq_printf(m, " / bound %s", bcm_proc_getifname(ifname, bo->ifindex));
         seq_printf(m, " <<<\n");
 
         list_for_each_entry(op, &bo->rx_ops, list) {
@@ -169,7 +173,7 @@ static int bcm_proc_show(struct seq_file *m, void *v)
                         continue;
 
                 seq_printf(m, "rx_op: %03X %-5s ",
-                                op->can_id, bcm_proc_getifname(op->ifindex));
+                                op->can_id, bcm_proc_getifname(ifname, op->ifindex));
                 seq_printf(m, "[%d]%c ", op->nframes,
                                 (op->flags & RX_CHECK_DLC)?'d':' ');
                 if (op->kt_ival1.tv64)
@@ -194,7 +198,8 @@ static int bcm_proc_show(struct seq_file *m, void *v)
         list_for_each_entry(op, &bo->tx_ops, list) {
 
                 seq_printf(m, "tx_op: %03X %s [%d] ",
-                                op->can_id, bcm_proc_getifname(op->ifindex),
+                                op->can_id,
+                                bcm_proc_getifname(ifname, op->ifindex),
                                 op->nframes);
 
                 if (op->kt_ival1.tv64)