netdev - RE: [bpf-next] bpf: Fix possible race in inc_misses

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Message-ID: <61f055a4b6451_2e4c520871@john.notmuch>
Date:   Tue, 25 Jan 2022 11:55:16 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     He Fengqing <hefengqing@...wei.com>, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, kafai@...com
Cc:     songliubraving@...com, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: RE: [bpf-next] bpf: Fix possible race in inc_misses_counter

He Fengqing wrote:
> It seems inc_misses_counter() suffers from same issue fixed in
> the commit d979617aa84d ("bpf: Fixes possible race in update_prog_stats()
> for 32bit arches"):
> As it can run while interrupts are enabled, it could
> be re-entered and the u64_stats syncp could be mangled.
> 
> Fixes: 9ed9e9ba2337 ("bpf: Count the number of times recursion was prevented")
> Signed-off-by: He Fengqing <hefengqing@...wei.com>
> ---
>  kernel/bpf/trampoline.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Appears possible through sleepable progs.

Acked-by: John Fastabend <john.fastabend@...il.com>

> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 4b6974a195c1..5e7edf913060 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -550,11 +550,12 @@ static __always_inline u64 notrace bpf_prog_start_time(void)
>  static void notrace inc_misses_counter(struct bpf_prog *prog)
>  {
>  	struct bpf_prog_stats *stats;
> +	unsigned int flags;
>  
>  	stats = this_cpu_ptr(prog->stats);
> -	u64_stats_update_begin(&stats->syncp);
> +	flags = u64_stats_update_begin_irqsave(&stats->syncp);
>  	u64_stats_inc(&stats->misses);
> -	u64_stats_update_end(&stats->syncp);
> +	u64_stats_update_end_irqrestore(&stats->syncp, flags);
>  }
>  
>  /* The logic is similar to bpf_prog_run(), but with an explicit
> -- 
> 2.25.1
>