Syzbot reported a use-after-free of the global vlan context on port vlan
destruction. When I added per-port vlan stats I missed the fact that the
global vlan context can be freed before the per-port vlan rcu callback.
There're a few different ways to deal with this, I've chosen to add a
new private flag that is set only when per-port stats are allocated so
we can directly check it on destruction without dereferencing the global
context at all. The flag is internally controlled by the kernel and
user-space isn't allowed to set it.
Fixes: 9163a0fc1f0c ("net: bridge: add support for per-port vlan stats")
Reported-by: syzbot+04681da557a0e49a52e5@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>
---
include/uapi/linux/if_bridge.h | 3 +++
net/bridge/br_netlink.c | 7 ++++++-
net/bridge/br_vlan.c | 3 ++-
3 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/if_bridge.h b/include/uapi/linux/if_bridge.h
index e41eda3c71f1..fa1f72276712 100644
--- a/include/uapi/linux/if_bridge.h
+++ b/include/uapi/linux/if_bridge.h
@@ -130,6 +130,9 @@ enum {
#define BRIDGE_VLAN_INFO_RANGE_BEGIN (1<<3) /* VLAN is start of vlan range */
#define BRIDGE_VLAN_INFO_RANGE_END (1<<4) /* VLAN is end of vlan range */
#define BRIDGE_VLAN_INFO_BRENTRY (1<<5) /* Global bridge VLAN entry */
+#define BRIDGE_VLAN_INFO_PORT_STATS (1<<6) /* Per-port VLAN stats */
+
+#define BRIDGE_VLAN_INFO_PRIVATE_FLAGS BRIDGE_VLAN_INFO_PORT_STATS
struct bridge_vlan_info {
__u16 flags;
diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index 3345f1984542..c600fedcfb76 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -527,8 +527,12 @@ int br_getlink(struct sk_buff *skb, u32 pid, u32 seq,
static int br_vlan_info(struct net_bridge *br, struct net_bridge_port *p,
int cmd, struct bridge_vlan_info *vinfo, bool *changed)
{
+ int err = -EINVAL;
bool curr_change;
- int err = 0;
+
+ /* don't allow user-space control over private flags */
+ if (vinfo->flags & BRIDGE_VLAN_INFO_PRIVATE_FLAGS)
+ return err;
switch (cmd) {
case RTM_SETLINK:
@@ -548,6 +552,7 @@ static int br_vlan_info(struct net_bridge *br, struct net_bridge_port *p,
break;
case RTM_DELLINK:
+ err = 0;
if (p) {
if (!nbp_vlan_delete(p, vinfo->vid))
*changed = true;
diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
index 8c9297a01947..004e1f8c5040 100644
--- a/net/bridge/br_vlan.c
+++ b/net/bridge/br_vlan.c
@@ -197,7 +197,7 @@ static void nbp_vlan_rcu_free(struct rcu_head *rcu)
v = container_of(rcu, struct net_bridge_vlan, rcu);
WARN_ON(br_vlan_is_master(v));
/* if we had per-port stats configured then free them here */
- if (v->brvlan->stats != v->stats)
+ if (v->flags & BRIDGE_VLAN_INFO_PORT_STATS)
free_percpu(v->stats);
v->stats = NULL;
kfree(v);
@@ -264,6 +264,7 @@ static int __vlan_add(struct net_bridge_vlan *v, u16 flags)
err = -ENOMEM;
goto out_filt;
}
+ v->flags |= BRIDGE_VLAN_INFO_PORT_STATS;
} else {
v->stats = masterv->stats;
}
--
2.17.2
