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wireguard: queueing: always return valid online CPU in wg_cpumask_choose_online()

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The function gets number of online CPUS, and uses it to search for
Nth cpu in cpu_online_mask.

If id == num_online_cpus() - 1, and one CPU gets offlined between
calling num_online_cpus() -> cpumask_nth(), there's a chance for
cpumask_nth() to find nothing and return >= nr_cpu_ids.

The caller code in __queue_work() tries to avoid that by checking the
returned CPU against WORK_CPU_UNBOUND, which is NR_CPUS. It's not the
same as '>= nr_cpu_ids'. On a typical Ubuntu desktop, NR_CPUS is 8192,
while nr_cpu_ids is the actual number of possible CPUs, say 8.

The non-existing cpu may later be passed to rcu_dereference() and
corrupt the logic. Fix it by switching from 'if' to 'while'.

Suggested-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://patch.msgid.link/20250910013644.4153708-3-Jason@zx2c4.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Yury Norov (NVIDIA)
2025-09-10 03:36:42 +02:00
committed by Jakub Kicinski
parent 5551d21284
commit 5bd8de2077
1 changed files with 1 additions and 1 deletions
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2
drivers/net/wireguard/queueing.h
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@@ -106,7 +106,7 @@ static inline int wg_cpumask_choose_online(int *stored_cpu, unsigned int id)
{
unsigned int cpu = *stored_cpu;
if (unlikely(cpu >= nr_cpu_ids || !cpu_online(cpu)))
while (unlikely(cpu >= nr_cpu_ids || !cpu_online(cpu)))
cpu = *stored_cpu = cpumask_nth(id % num_online_cpus(), cpu_online_mask);
return cpu;