netdev - Re: [PATCH v4 net] ps3/gelic: Fix SKB allocation

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Date: Mon, 19 Feb 2024 17:20:18 +0900
From: Geoff Levand <geoff@...radead.org>
To: Paolo Abeni <pabeni@...hat.com>, sambat goson <sombat3960@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 net] ps3/gelic: Fix SKB allocation

On 2/16/24 19:06, Paolo Abeni wrote:
> On Fri, 2024-02-16 at 18:37 +0900, Geoff Levand wrote:
>> On 2/13/24 21:07, Paolo Abeni wrote:
>>> On Sat, 2024-02-10 at 17:15 +0900, Geoff Levand wrote:
>>>> Commit 3ce4f9c3fbb3 ("net/ps3_gelic_net: Add gelic_descr structures") of
>>>> 6.8-rc1 did not allocate a network SKB for the gelic_descr, resulting in a
>>>> kernel panic when the SKB variable (struct gelic_descr.skb) was accessed.
>>>>
>>>> This fix changes the way the napi buffer and corresponding SKB are
>>>> allocated and managed.
>>>
>>> I think this is not what Jakub asked on v3.
>>>
>>> Isn't something alike the following enough to fix the NULL ptr deref?
>>>
>>> Thanks,
>>>
>>> Paolo
>>> ---
>>> diff --git a/drivers/net/ethernet/toshiba/ps3_gelic_net.c b/drivers/net/ethernet/toshiba/ps3_gelic_net.c
>>> index d5b75af163d3..51ee6075653f 100644
>>> --- a/drivers/net/ethernet/toshiba/ps3_gelic_net.c
>>> +++ b/drivers/net/ethernet/toshiba/ps3_gelic_net.c
>>> @@ -395,7 +395,6 @@ static int gelic_descr_prepare_rx(struct gelic_card *card,
>>>         descr->hw_regs.data_error = 0;
>>>         descr->hw_regs.payload.dev_addr = 0;
>>>         descr->hw_regs.payload.size = 0;
>>> -       descr->skb = NULL;
>>
>> The reason we set the SKB pointer to NULL here is so we can
>> detect if an SKB has been allocated or not.  If the SKB pointer
>> is not NULL, then we delete it.
>>
>> If we just let the SKB pointer be some random value then later
>> we will try to delete some random address.
> 
> Note that this specific 'skb = NULL' assignment happens just after a
> successful allocation and just before unconditional dereference of such
> ptr:
> 
>         descr->skb = netdev_alloc_skb(*card->netdev, rx_skb_size);
>         if (!descr->skb) {
>                 descr->hw_regs.payload.dev_addr = 0; /* tell DMAC don't touch memory */
>                 return -ENOMEM;
>         }
> 
>         descr->hw_regs.dmac_cmd_status = 0;
>         descr->hw_regs.result_size = 0;
>         descr->hw_regs.valid_size = 0;
>         descr->hw_regs.data_error = 0;
>         descr->hw_regs.payload.dev_addr = 0;
>         descr->hw_regs.payload.size = 0;
> 	// XXX here skb is not NULL and valid 
>         descr->skb = NULL;

I see your point now.  I'll send out a fix-up patch that just
moves the initialization of the descr to before the allocation
of the SKB.  Thanks.

-Geoff