CVE-2024-40980

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

drop_monitor: replace spin_lock by raw_spin_lock

trace_drop_common() is called with preemption disabled, and it acquires

a spin_lock. This is problematic for RT kernels because spin_locks are

sleeping locks in this configuration, which causes the following splat:

BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48

in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 449, name: rcuc/47

preempt_count: 1, expected: 0

RCU nest depth: 2, expected: 2

5 locks held by rcuc/47/449:

#0: ff1100086ec30a60 ((softirq_ctrl.lock)){+.+.}-{2:2}, at: __local_bh_disable_ip+0x105/0x210

#1: ffffffffb394a280 (rcu_read_lock){....}-{1:2}, at: rt_spin_lock+0xbf/0x130

#2: ffffffffb394a280 (rcu_read_lock){....}-{1:2}, at: __local_bh_disable_ip+0x11c/0x210

#3: ffffffffb394a160 (rcu_callback){....}-{0:0}, at: rcu_do_batch+0x360/0xc70

#4: ff1100086ee07520 (&data->lock){+.+.}-{2:2}, at: trace_drop_common.constprop.0+0xb5/0x290

irq event stamp: 139909

hardirqs last enabled at (139908): [<ffffffffb1df2b33>] _raw_spin_unlock_irqrestore+0x63/0x80

hardirqs last disabled at (139909): [<ffffffffb19bd03d>] trace_drop_common.constprop.0+0x26d/0x290

softirqs last enabled at (139892): [<ffffffffb07a1083>] __local_bh_enable_ip+0x103/0x170

softirqs last disabled at (139898): [<ffffffffb0909b33>] rcu_cpu_kthread+0x93/0x1f0

Preemption disabled at:

[<ffffffffb1de786b>] rt_mutex_slowunlock+0xab/0x2e0

CPU: 47 PID: 449 Comm: rcuc/47 Not tainted 6.9.0-rc2-rt1+ #7

Hardware name: Dell Inc. PowerEdge R650/0Y2G81, BIOS 1.6.5 04/15/2022

Call Trace:

<TASK>

dump_stack_lvl+0x8c/0xd0

dump_stack+0x14/0x20

__might_resched+0x21e/0x2f0

rt_spin_lock+0x5e/0x130

? trace_drop_common.constprop.0+0xb5/0x290

? skb_queue_purge_reason.part.0+0x1bf/0x230

trace_drop_common.constprop.0+0xb5/0x290

? preempt_count_sub+0x1c/0xd0

? _raw_spin_unlock_irqrestore+0x4a/0x80

? __pfx_trace_drop_common.constprop.0+0x10/0x10

? rt_mutex_slowunlock+0x26a/0x2e0

? skb_queue_purge_reason.part.0+0x1bf/0x230

? __pfx_rt_mutex_slowunlock+0x10/0x10

? skb_queue_purge_reason.part.0+0x1bf/0x230

trace_kfree_skb_hit+0x15/0x20

trace_kfree_skb+0xe9/0x150

kfree_skb_reason+0x7b/0x110

skb_queue_purge_reason.part.0+0x1bf/0x230

? __pfx_skb_queue_purge_reason.part.0+0x10/0x10

? mark_lock.part.0+0x8a/0x520

...

trace_drop_common() also disables interrupts, but this is a minor issue

because we could easily replace it with a local_lock.

Replace the spin_lock with raw_spin_lock to avoid sleeping in atomic

context.