linux-kernel - Re: [PATCH v1] ptp: ocp: fix NULL deref in _signal_summary

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Message-ID: <b6aea926-ebb6-48fe-a1be-6f428a648eae@linux.dev>
Date: Mon, 14 Apr 2025 10:37:26 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Sagi Maimon <maimon.sagi@...il.com>, jonathan.lemon@...il.com,
 richardcochran@...il.com, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v1] ptp: ocp: fix NULL deref in _signal_summary_show

On 14/04/2025 09:54, Sagi Maimon wrote:
> Sysfs signal show operations can invoke _signal_summary_show before
> signal_out array elements are initialized, causing a NULL pointer
> dereference. Add NULL checks for signal_out elements to prevent kernel
> crashes.
> 
> Fixes: b325af3cfab9 ("ptp: ocp: Add signal generators and update sysfs nodes")
> Signed-off-by: Sagi Maimon <maimon.sagi@...il.com>
> ---
>   drivers/ptp/ptp_ocp.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
> index 7945c6be1f7c..4c7893539cec 100644
> --- a/drivers/ptp/ptp_ocp.c
> +++ b/drivers/ptp/ptp_ocp.c
> @@ -3963,6 +3963,9 @@ _signal_summary_show(struct seq_file *s, struct ptp_ocp *bp, int nr)
>   	bool on;
>   	u32 val;
>   
> +	if (!bp->signal_out[nr])
> +		return;
> +
>   	on = signal->running;
>   	sprintf(label, "GEN%d", nr + 1);
>   	seq_printf(s, "%7s: %s, period:%llu duty:%d%% phase:%llu pol:%d",

That's not correct, the dereference of bp->signal_out[nr] happens before
the check. But I just wonder how can that even happen?

I believe the proper fix is to move ptp_ocp_attr_group_add() closer to
the end of ptp_ocp_adva_board_init() like it's done for other boards.

--
pw-bot: cr