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+04681da557a0e49a5...@syzkaller.appspotmail.com Signed-off-by: Nikolay Aleksandrov <niko...@cumulusnetworks.com> --- v2: cosmetic change, move the check to br_process_vlan_info where the other checks are done include/uapi/linux/if_bridge.h | 3 +++ net/bridge/br_netlink.c | 4 ++++ net/bridge/br_vlan.c | 3 ++- 3 files changed, 9 insertions(+), 1 deletion(-) 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..a017ed566b67 100644 --- a/net/bridge/br_netlink.c +++ b/net/bridge/br_netlink.c @@ -573,6 +573,10 @@ static int br_process_vlan_info(struct net_bridge *br, if (!vinfo_curr->vid || vinfo_curr->vid >= VLAN_VID_MASK) return -EINVAL; + /* don't allow user-space control over private flags */ + if (vinfo_curr->flags & BRIDGE_VLAN_INFO_PRIVATE_FLAGS) + return -EINVAL; + if (vinfo_curr->flags & BRIDGE_VLAN_INFO_RANGE_BEGIN) { /* check if we are already processing a range */ if (*vinfo_last) 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