CVE-2025-39773

In the Linux kernel, the following vulnerability has been resolved:

net: bridge: fix soft lockup in br_multicast_query_expired()

When set multicast_query_interval to a large value, the local variable

'time' in br_multicast_send_query() may overflow. If the time is smaller

than jiffies, the timer will expire immediately, and then call mod_timer()

again, which creates a loop and may trigger the following soft lockup

issue.

watchdog: BUG: soft lockup - CPU#1 stuck for 221s! [rb_consumer:66]

CPU: 1 UID: 0 PID: 66 Comm: rb_consumer Not tainted 6.16.0+ #259 PREEMPT(none)

Call Trace:

<IRQ>

__netdev_alloc_skb+0x2e/0x3a0

br_ip6_multicast_alloc_query+0x212/0x1b70

__br_multicast_send_query+0x376/0xac0

br_multicast_send_query+0x299/0x510

br_multicast_query_expired.constprop.0+0x16d/0x1b0

call_timer_fn+0x3b/0x2a0

__run_timers+0x619/0x950

run_timer_softirq+0x11c/0x220

handle_softirqs+0x18e/0x560

__irq_exit_rcu+0x158/0x1a0

sysvec_apic_timer_interrupt+0x76/0x90

</IRQ>

This issue can be reproduced with:

ip link add br0 type bridge

echo 1 > /sys/class/net/br0/bridge/multicast_querier

echo 0xffffffffffffffff >

/sys/class/net/br0/bridge/multicast_query_interval

ip link set dev br0 up

The multicast_startup_query_interval can also cause this issue. Similar to

the commit 99b40610956a ("net: bridge: mcast: add and enforce query

interval minimum"), add check for the query interval maximum to fix this

issue.