[PATCH net-next] net: dsa: Fix use after free in dsa_switch_remove()

The order in which the ports are deleted from the list and freed and the
call to dsa_tree_remove_switch() is done is reversed, which leads to an
use after free condition. Reverse the two: first tear down the ports and
switch from the fabric, then free the ports associated with that switch
fabric.

Fixes: 05f294a85235 ("net: dsa: allocate ports on touch")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 net/dsa/dsa2.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index ff2fa3950c62..9ef2caa13f27 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c

@@ -874,12 +874,13 @@ static void dsa_switch_remove(struct dsa_switch *ds)
 	struct dsa_switch_tree *dst = ds->dst;
 	struct dsa_port *dp, *next;
 
+	dsa_tree_teardown(dst);
+
 	list_for_each_entry_safe(dp, next, &dst->ports, list) {
 		list_del(&dp->list);
 		kfree(dp);
 	}
 
-	dsa_tree_teardown(dst);
 	dsa_tree_put(dst);
 }
 

-- 
2.17.1

On Sat,  2 Nov 2019 20:13:26 -0700, Florian Fainelli [off-list ref] wrote:

The order in which the ports are deleted from the list and freed and the
call to dsa_tree_remove_switch() is done is reversed, which leads to an

s/dsa_tree_remove_switch/dsa_switch_remove/

use after free condition. Reverse the two: first tear down the ports and
switch from the fabric, then free the ports associated with that switch
fabric.

Fixes: 05f294a85235 ("net: dsa: allocate ports on touch")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Thanks for reporting and fixing this!

Reviewed-by: Vivien Didelot <redacted>

From: Florian Fainelli <f.fainelli@gmail.com>
Date: Sat,  2 Nov 2019 20:13:26 -0700

The order in which the ports are deleted from the list and freed and the
call to dsa_tree_remove_switch() is done is reversed, which leads to an
use after free condition. Reverse the two: first tear down the ports and
switch from the fabric, then free the ports associated with that switch
fabric.

Fixes: 05f294a85235 ("net: dsa: allocate ports on touch")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Applied.