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

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Message-ID: <aa9a1485-0a0b-442b-b126-a00ee5d4801c@linux.dev>
Date: Mon, 14 Apr 2025 12:09:36 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Sagi Maimon <maimon.sagi@...il.com>
Cc: jonathan.lemon@...il.com, richardcochran@...il.com,
 andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, 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 11:56, Sagi Maimon wrote:
> On Mon, Apr 14, 2025 at 12:37 PM Vadim Fedorenko
> <vadim.fedorenko@...ux.dev> wrote:
>>
>> 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?
>>
> The scenario (our case): on ptp_ocp_adva_board_init we
> initiate only signals 0 and 1 so 2 and 3 are NULL.
> Later ptp_ocp_summary_show runs on all 4 signals and calls _signal_summary_show
> when calling signal 2 or 3  the dereference occurs.
> can you please explain: " the dereference of bp->signal_out[nr] happens before
> the check", where exactly? do you mean in those lines:
> struct signal_reg __iomem *reg = bp->signal_out[nr]->mem;
    ^^^
yes, this is the line which dereferences the pointer.

but in case you have only 2 pins to configure, why the driver exposes 4
SMAs? You can simply adjust the attributes (adva_timecard_attrs).

> struct ptp_ocp_signal *signal = &bp->signal[nr];
>> 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