6.15-stable review patch. If anyone has any objections, please let me know.
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From: Ido Schimmel idosch@nvidia.com
[ Upstream commit 7544f3f5b0b58c396f374d060898b5939da31709 ]
The bridge maintains a global list of ports behind which a multicast router resides. The list is consulted during forwarding to ensure multicast packets are forwarded to these ports even if the ports are not member in the matching MDB entry.
When per-VLAN multicast snooping is enabled, the per-port multicast context is disabled on each port and the port is removed from the global router port list:
# ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 # ip link add name dummy1 up master br1 type dummy # ip link set dev dummy1 type bridge_slave mcast_router 2 $ bridge -d mdb show | grep router router ports on br1: dummy1 # ip link set dev br1 type bridge mcast_vlan_snooping 1 $ bridge -d mdb show | grep router
However, the port can be re-added to the global list even when per-VLAN multicast snooping is enabled:
# ip link set dev dummy1 type bridge_slave mcast_router 0 # ip link set dev dummy1 type bridge_slave mcast_router 2 $ bridge -d mdb show | grep router router ports on br1: dummy1
Since commit 4b30ae9adb04 ("net: bridge: mcast: re-implement br_multicast_{enable, disable}_port functions"), when per-VLAN multicast snooping is enabled, multicast disablement on a port will disable the per-{port, VLAN} multicast contexts and not the per-port one. As a result, a port will remain in the global router port list even after it is deleted. This will lead to a use-after-free [1] when the list is traversed (when adding a new port to the list, for example):
# ip link del dev dummy1 # ip link add name dummy2 up master br1 type dummy # ip link set dev dummy2 type bridge_slave mcast_router 2
Similarly, stale entries can also be found in the per-VLAN router port list. When per-VLAN multicast snooping is disabled, the per-{port, VLAN} contexts are disabled on each port and the port is removed from the per-VLAN router port list:
# ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 mcast_vlan_snooping 1 # ip link add name dummy1 up master br1 type dummy # bridge vlan add vid 2 dev dummy1 # bridge vlan global set vid 2 dev br1 mcast_snooping 1 # bridge vlan set vid 2 dev dummy1 mcast_router 2 $ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1 # ip link set dev br1 type bridge mcast_vlan_snooping 0 $ bridge vlan global show dev br1 vid 2 | grep router
However, the port can be re-added to the per-VLAN list even when per-VLAN multicast snooping is disabled:
# bridge vlan set vid 2 dev dummy1 mcast_router 0 # bridge vlan set vid 2 dev dummy1 mcast_router 2 $ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1
When the VLAN is deleted from the port, the per-{port, VLAN} multicast context will not be disabled since multicast snooping is not enabled on the VLAN. As a result, the port will remain in the per-VLAN router port list even after it is no longer member in the VLAN. This will lead to a use-after-free [2] when the list is traversed (when adding a new port to the list, for example):
# ip link add name dummy2 up master br1 type dummy # bridge vlan add vid 2 dev dummy2 # bridge vlan del vid 2 dev dummy1 # bridge vlan set vid 2 dev dummy2 mcast_router 2
Fix these issues by removing the port from the relevant (global or per-VLAN) router port list in br_multicast_port_ctx_deinit(). The function is invoked during port deletion with the per-port multicast context and during VLAN deletion with the per-{port, VLAN} multicast context.
Note that deleting the multicast router timer is not enough as it only takes care of the temporary multicast router states (1 or 3) and not the permanent one (2).
[1] BUG: KASAN: slab-out-of-bounds in br_multicast_add_router.part.0+0x3f1/0x560 Write of size 8 at addr ffff888004a67328 by task ip/384 [...] Call Trace: <TASK> dump_stack_lvl+0x6f/0xa0 print_address_description.constprop.0+0x6f/0x350 print_report+0x108/0x205 kasan_report+0xdf/0x110 br_multicast_add_router.part.0+0x3f1/0x560 br_multicast_set_port_router+0x74e/0xac0 br_setport+0xa55/0x1870 br_port_slave_changelink+0x95/0x120 __rtnl_newlink+0x5e8/0xa40 rtnl_newlink+0x627/0xb00 rtnetlink_rcv_msg+0x6fb/0xb70 netlink_rcv_skb+0x11f/0x350 netlink_unicast+0x426/0x710 netlink_sendmsg+0x75a/0xc20 __sock_sendmsg+0xc1/0x150 ____sys_sendmsg+0x5aa/0x7b0 ___sys_sendmsg+0xfc/0x180 __sys_sendmsg+0x124/0x1c0 do_syscall_64+0xbb/0x360 entry_SYSCALL_64_after_hwframe+0x4b/0x53
[2] BUG: KASAN: slab-use-after-free in br_multicast_add_router.part.0+0x378/0x560 Read of size 8 at addr ffff888009f00840 by task bridge/391 [...] Call Trace: <TASK> dump_stack_lvl+0x6f/0xa0 print_address_description.constprop.0+0x6f/0x350 print_report+0x108/0x205 kasan_report+0xdf/0x110 br_multicast_add_router.part.0+0x378/0x560 br_multicast_set_port_router+0x6f9/0xac0 br_vlan_process_options+0x8b6/0x1430 br_vlan_rtm_process_one+0x605/0xa30 br_vlan_rtm_process+0x396/0x4c0 rtnetlink_rcv_msg+0x2f7/0xb70 netlink_rcv_skb+0x11f/0x350 netlink_unicast+0x426/0x710 netlink_sendmsg+0x75a/0xc20 __sock_sendmsg+0xc1/0x150 ____sys_sendmsg+0x5aa/0x7b0 ___sys_sendmsg+0xfc/0x180 __sys_sendmsg+0x124/0x1c0 do_syscall_64+0xbb/0x360 entry_SYSCALL_64_after_hwframe+0x4b/0x53
Fixes: 2796d846d74a ("net: bridge: vlan: convert mcast router global option to per-vlan entry") Fixes: 4b30ae9adb04 ("net: bridge: mcast: re-implement br_multicast_{enable, disable}_port functions") Reported-by: syzbot+7bfa4b72c6a5da128d32@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/684c18bd.a00a0220.279073.000b.GAE@google.com/T/ Signed-off-by: Ido Schimmel idosch@nvidia.com Link: https://patch.msgid.link/20250619182228.1656906-1-idosch@nvidia.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/bridge/br_multicast.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index 7e0b2362b9ee5..d35a409b5e4aa 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -2014,10 +2014,19 @@ void br_multicast_port_ctx_init(struct net_bridge_port *port,
void br_multicast_port_ctx_deinit(struct net_bridge_mcast_port *pmctx) { + struct net_bridge *br = pmctx->port->br; + bool del = false; + #if IS_ENABLED(CONFIG_IPV6) timer_delete_sync(&pmctx->ip6_mc_router_timer); #endif timer_delete_sync(&pmctx->ip4_mc_router_timer); + + spin_lock_bh(&br->multicast_lock); + del |= br_ip6_multicast_rport_del(pmctx); + del |= br_ip4_multicast_rport_del(pmctx); + br_multicast_rport_del_notify(pmctx, del); + spin_unlock_bh(&br->multicast_lock); }
int br_multicast_add_port(struct net_bridge_port *port)