From: Yonghong Song <yhs@meta.com>
To: starmiku1207184332@gmail.com, ast@kernel.org,
daniel@iogearbox.net, john.fastabend@gmail.com,
andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
yhs@fb.com, kpsingh@kernel.org, sdf@google.com,
haoluo@google.com, jolsa@kernel.org, davem@davemloft.net,
kuba@kernel.org, hawk@kernel.org
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org
Subject: Re: [bug] kernel: bpf: syscall: a possible sleep-in-atomic bug in __bpf_prog_put()
Date: Tue, 16 May 2023 10:08:17 -0700 [thread overview]
Message-ID: <e37c0a65-a3f6-e2e6-c2ad-367db20253a0@meta.com> (raw)
In-Reply-To: <20230516111823.2103536-1-starmiku1207184332@gmail.com>
On 5/16/23 4:18 AM, starmiku1207184332@gmail.com wrote:
> From: Teng Qi <starmiku1207184332@gmail.com>
>
> Hi, bpf developers,
>
> We are developing a static tool to check the matching between helpers and the
> context of hooks. During our analysis, we have discovered some important
> findings that we would like to report.
>
> ‘kernel/bpf/syscall.c: 2097 __bpf_prog_put()’ shows that function
> bpf_prog_put_deferred() won`t be called in the condition of
> ‘in_irq() || irqs_disabled()’.
> if (in_irq() || irqs_disabled()) {
> INIT_WORK(&aux->work, bpf_prog_put_deferred);
> schedule_work(&aux->work);
> } else {
>
> bpf_prog_put_deferred(&aux->work);
> }
>
> We suspect this condition exists because there might be sleepable operations
> in the callees of the bpf_prog_put_deferred() function:
> kernel/bpf/syscall.c: 2097 __bpf_prog_put()
> kernel/bpf/syscall.c: 2084 bpf_prog_put_deferred()
> kernel/bpf/syscall.c: 2063 __bpf_prog_put_noref()
> kvfree(prog->aux->jited_linfo);
> kvfree(prog->aux->linfo);
Looks like you only have suspicion here. Could you find a real violation
here where __bpf_prog_put() is called with !in_irq() &&
!irqs_disabled(), but inside spin_lock or rcu read lock? I have not seen
things like that.
>
> Additionally, we found that array prog->aux->jited_linfo is initialized in
> ‘kernel/bpf/core.c: 157 bpf_prog_alloc_jited_linfo()’:
> prog->aux->jited_linfo = kvcalloc(prog->aux->nr_linfo,
> sizeof(*prog->aux->jited_linfo), bpf_memcg_flags(GFP_KERNEL | __GFP_NOWARN));
Any problem here?
>
> Our question is whether the condition 'in_irq() || irqs_disabled() == false' is
> sufficient for calling 'kvfree'. We are aware that calling 'kvfree' within the
> context of a spin lock or an RCU lock is unsafe.
>
> Therefore, we propose modifying the condition to include in_atomic(). Could we
> update the condition as follows: "in_irq() || irqs_disabled() || in_atomic()"?
>
> Thank you! We look forward to your feedback.
>
> Signed-off-by: Teng Qi <starmiku1207184332@gmail.com>
next prev parent reply other threads:[~2023-05-16 17:09 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-16 11:18 [bug] kernel: bpf: syscall: a possible sleep-in-atomic bug in __bpf_prog_put() starmiku1207184332
2023-05-16 17:08 ` Yonghong Song [this message]
[not found] ` <CALyQVax8X63qekZVhvRTmZFFs+ucPKRkBB7UnRZk6Hu3ggi7Og@mail.gmail.com>
2023-05-21 3:44 ` Yonghong Song
[not found] ` <CALyQVazb=D1ejapiFdTnan6JbjFJA2q9ifhSsmF4OC9MDz3oAw@mail.gmail.com>
2023-05-23 4:33 ` Yonghong Song
2023-05-24 12:42 ` Teng Qi
2023-05-24 19:34 ` Yonghong Song
2023-05-24 19:44 ` Alexei Starovoitov
2023-05-25 5:37 ` Yonghong Song
2023-06-11 13:02 ` Teng Qi
2023-06-12 0:01 ` Yonghong Song
2023-06-19 9:05 ` Teng Qi
2023-06-19 19:01 ` Yonghong Song
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