[PATCH 6.1 272/473] net: bridge: mst: fix vlan use-after-free

Greg Kroah-Hartman
2024-06-06T14:16:42Z

From: Nikolay Aleksandrov <razor@blackwall.org>

[ Upstream commit 3a7c1661ae1383364cd6092d851f5e5da64d476b ]

syzbot reported a suspicious rcu usage[1] in bridge's mst code. While
fixing it I noticed that nothing prevents a vlan to be freed while
walking the list from the same path (br forward delay timer). Fix the rcu
usage and also make sure we are not accessing freed memory by making
br_mst_vlan_set_state use rcu read lock.

[1]
WARNING: suspicious RCU usage
6.9.0-rc6-syzkaller #0 Not tainted
-----------------------------
net/bridge/br_private.h:1599 suspicious rcu_dereference_protected() usage!
...
stack backtrace:
CPU: 1 PID: 8017 Comm: syz-executor.1 Not tainted 6.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
lockdep_rcu_suspicious+0x221/0x340 kernel/locking/lockdep.c:6712
nbp_vlan_group net/bridge/br_private.h:1599 [inline]
br_mst_set_state+0x1ea/0x650 net/bridge/br_mst.c:105
br_set_state+0x28a/0x7b0 net/bridge/br_stp.c:47
br_forward_delay_timer_expired+0x176/0x440 net/bridge/br_stp_timer.c:88
call_timer_fn+0x18e/0x650 kernel/time/timer.c:1793
expire_timers kernel/time/timer.c:1844 [inline]
__run_timers kernel/time/timer.c:2418 [inline]
__run_timer_base+0x66a/0x8e0 kernel/time/timer.c:2429
run_timer_base kernel/time/timer.c:2438 [inline]
run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2448
__do_softirq+0x2c6/0x980 kernel/softirq.c:554
invoke_softirq kernel/softirq.c:428 [inline]
__irq_exit_rcu+0xf2/0x1c0 kernel/softirq.c:633
irq_exit_rcu+0x9/0x30 kernel/softirq.c:645
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1043
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:lock_acquire+0x264/0x550 kernel/locking/lockdep.c:5758
Code: 2b 00 74 08 4c 89 f7 e8 ba d1 84 00 f6 44 24 61 02 0f 85 85 01 00 00 41 f7 c7 00 02 00 00 74 01 fb 48 c7 44 24 40 0e 36 e0 45 <4b> c7 44 25 00 00 00 00 00 43 c7 44 25 09 00 00 00 00 43 c7 44 25
RSP: 0018:ffffc90013657100 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 1ffff920026cae2c RCX: 0000000000000001
RDX: dffffc0000000000 RSI: ffffffff8bcaca00 RDI: ffffffff8c1eaa60
RBP: ffffc90013657260 R08: ffffffff92efe507 R09: 1ffffffff25dfca0
R10: dffffc0000000000 R11: fffffbfff25dfca1 R12: 1ffff920026cae28
R13: dffffc0000000000 R14: ffffc90013657160 R15: 0000000000000246

Fixes: ec7328b59176 ("net: bridge: mst: Multiple Spanning Tree (MST) mode")
Reported-by: syzbot+fa04eb8a56fd923fc5d8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fa04eb8a56fd923fc5d8
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/bridge/br_mst.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/bridge/br_mst.c b/net/bridge/br_mst.c
index ee680adcee179..3c66141d34d62 100644
--- a/net/bridge/br_mst.c
+++ b/net/bridge/br_mst.c
@@ -78,7 +78,7 @@ static void br_mst_vlan_set_state(struct net_bridge_port *p, struct net_bridge_v
{
struct net_bridge_vlan_group *vg = nbp_vlan_group(p);

- if (v->state == state)
+ if (br_vlan_get_state(v) == state)
return;

br_vlan_set_state(v, state);
@@ -100,11 +100,12 @@ int br_mst_set_state(struct net_bridge_port *p, u16 msti, u8 state,
};
struct net_bridge_vlan_group *vg;
struct net_bridge_vlan *v;
- int err;
+ int err = 0;

+ rcu_read_lock();
vg = nbp_vlan_group(p);
if (!vg)
- return 0;
+ goto out;

/* MSTI 0 (CST) state changes are notified via the regular
* SWITCHDEV_ATTR_ID_PORT_STP_STATE.
@@ -112,17 +113,20 @@ int br_mst_set_state(struct net_bridge_port *p, u16 msti, u8 state,
if (msti) {
err = switchdev_port_attr_set(p->dev, &attr, extack);
if (err && err != -EOPNOTSUPP)
- return err;
+ goto out;
}

- list_for_each_entry(v, &vg->vlan_list, vlist) {
+ err = 0;
+ list_for_each_entry_rcu(v, &vg->vlan_list, vlist) {
if (v->brvlan->msti != msti)
continue;

br_mst_vlan_set_state(p, v, state);
}

- return 0;
+out:
+ rcu_read_unlock();
+ return err;
}

static void br_mst_vlan_sync_state(struct net_bridge_vlan *pv, u16 msti)
--
2.43.0