6.6-stable review patch. If anyone has any objections, please let me know.
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From: Nikolay Aleksandrov razor@blackwall.org
[ Upstream commit 8dca36978aa80bab9d4da130c211db75c9e00048 ]
syzbot reported[1] a use-after-free when deleting an expired fdb. It is due to a race condition between learning still happening and a port being deleted, after all its fdbs have been flushed. The port's state has been toggled to disabled so no learning should happen at that time, but if we have MST enabled, it will bypass the port's state, that together with VLAN filtering disabled can lead to fdb learning at a time when it shouldn't happen while the port is being deleted. VLAN filtering must be disabled because we flush the port VLANs when it's being deleted which will stop learning. This fix adds a check for the port's vlan group which is initialized to NULL when the port is getting deleted, that avoids the port state bypass. When MST is enabled there would be a minimal new overhead in the fast-path because the port's vlan group pointer is cache-hot.
[1] https://syzkaller.appspot.com/bug?extid=dd280197f0f7ab3917be
Fixes: ec7328b59176 ("net: bridge: mst: Multiple Spanning Tree (MST) mode") Reported-by: syzbot+dd280197f0f7ab3917be@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/69088ffa.050a0220.29fc44.003d.GAE@google.com/ Signed-off-by: Nikolay Aleksandrov razor@blackwall.org Reviewed-by: Ido Schimmel idosch@nvidia.com Link: https://patch.msgid.link/20251105111919.1499702-2-razor@blackwall.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/bridge/br_forward.c | 2 +- net/bridge/br_input.c | 4 ++-- net/bridge/br_private.h | 8 +++++--- 3 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c index 49dd8cd526f46..e9f09cdb9848e 100644 --- a/net/bridge/br_forward.c +++ b/net/bridge/br_forward.c @@ -25,7 +25,7 @@ static inline int should_deliver(const struct net_bridge_port *p,
vg = nbp_vlan_group_rcu(p); return ((p->flags & BR_HAIRPIN_MODE) || skb->dev != p->dev) && - (br_mst_is_enabled(p->br) || p->state == BR_STATE_FORWARDING) && + (br_mst_is_enabled(p) || p->state == BR_STATE_FORWARDING) && br_allowed_egress(vg, skb) && nbp_switchdev_allowed_egress(p, skb) && !br_skb_isolated(p, skb); } diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c index e09000e38d071..951330c1a813b 100644 --- a/net/bridge/br_input.c +++ b/net/bridge/br_input.c @@ -93,7 +93,7 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
br = p->br;
- if (br_mst_is_enabled(br)) { + if (br_mst_is_enabled(p)) { state = BR_STATE_FORWARDING; } else { if (p->state == BR_STATE_DISABLED) @@ -411,7 +411,7 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb) return RX_HANDLER_PASS;
forward: - if (br_mst_is_enabled(p->br)) + if (br_mst_is_enabled(p)) goto defer_stp_filtering;
switch (p->state) { diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h index ef98ec4c3f51d..798960ef2dcd0 100644 --- a/net/bridge/br_private.h +++ b/net/bridge/br_private.h @@ -1880,10 +1880,12 @@ static inline bool br_vlan_state_allowed(u8 state, bool learn_allow) /* br_mst.c */ #ifdef CONFIG_BRIDGE_VLAN_FILTERING DECLARE_STATIC_KEY_FALSE(br_mst_used); -static inline bool br_mst_is_enabled(struct net_bridge *br) +static inline bool br_mst_is_enabled(const struct net_bridge_port *p) { + /* check the port's vlan group to avoid racing with port deletion */ return static_branch_unlikely(&br_mst_used) && - br_opt_get(br, BROPT_MST_ENABLED); + br_opt_get(p->br, BROPT_MST_ENABLED) && + rcu_access_pointer(p->vlgrp); }
int br_mst_set_state(struct net_bridge_port *p, u16 msti, u8 state, @@ -1898,7 +1900,7 @@ int br_mst_fill_info(struct sk_buff *skb, int br_mst_process(struct net_bridge_port *p, const struct nlattr *mst_attr, struct netlink_ext_ack *extack); #else -static inline bool br_mst_is_enabled(struct net_bridge *br) +static inline bool br_mst_is_enabled(const struct net_bridge_port *p) { return false; }