net: dsa: Fix stale cpu_switch reference after unbind then bind
authorFlorian Fainelli <f.fainelli@gmail.com>
Sat, 3 Jun 2017 05:05:23 +0000 (22:05 -0700)
committerDavid S. Miller <davem@davemloft.net>
Mon, 5 Jun 2017 02:55:17 +0000 (22:55 -0400)
Commit 9520ed8fb841 ("net: dsa: use cpu_switch instead of ds[0]")
replaced the use of dst->ds[0] with dst->cpu_switch since that is
functionally equivalent, however, we can now run into an use after free
scenario after unbinding then rebinding the switch driver.

The use after free happens because we do correctly initialize
dst->cpu_switch the first time we probe in dsa_cpu_parse(), then we
unbind the driver: dsa_dst_unapply() is called, and we rebind again.
dst->cpu_switch now points to a freed "ds" structure, and so when we
finally dereference it in dsa_cpu_port_ethtool_setup(), we oops.

To fix this, simply set dst->cpu_switch to NULL in dsa_dst_unapply()
which guarantees that we always correctly re-assign dst->cpu_switch in
dsa_cpu_parse().

Fixes: 9520ed8fb841 ("net: dsa: use cpu_switch instead of ds[0]")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
net/dsa/dsa2.c

index 033b3bfb63dc1887b15b3e08f00a00f70b706ec4..7796580e99ee2c57cdd5503130c8ec2e121d879a 100644 (file)
@@ -484,8 +484,10 @@ static void dsa_dst_unapply(struct dsa_switch_tree *dst)
                dsa_ds_unapply(dst, ds);
        }
 
-       if (dst->cpu_switch)
+       if (dst->cpu_switch) {
                dsa_cpu_port_ethtool_restore(dst->cpu_switch);
+               dst->cpu_switch = NULL;
+       }
 
        pr_info("DSA: tree %d unapplied\n", dst->tree);
        dst->applied = false;