linux-kernel - Re: [Intel-wired-lan] [PATCH][next] ixgbe: Fix out-of-bounds warning in ixgbe_host_interface

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Message-ID: <944f3971-544f-49b4-1351-2eb3ee20588b@embeddedor.com>
Date:   Wed, 17 Mar 2021 14:50:27 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        intel-wired-lan@...ts.osuosl.org, linux-hardening@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH][next] ixgbe: Fix out-of-bounds warning
 in ixgbe_host_interface_command()



On 3/17/21 15:10, Jann Horn wrote:
> On Wed, Mar 17, 2021 at 9:04 PM Gustavo A. R. Silva
> <gustavo@...eddedor.com> wrote:
>> On 3/17/21 13:57, Jann Horn wrote:
>>>>>> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
>>>>>> index 62ddb452f862..bff3dc1af702 100644
>>>>>> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
>>>>>> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
>>>>>> @@ -3679,7 +3679,7 @@ s32 ixgbe_host_interface_command(struct ixgbe_hw *hw, void *buffer,
>>>>>>         u32 hdr_size = sizeof(struct ixgbe_hic_hdr);
>>>>>>         union {
>>>>>>                 struct ixgbe_hic_hdr hdr;
>>>>>> -               u32 u32arr[1];
>>>>>> +               u32 *u32arr;
>>>>>>         } *bp = buffer;
>>>>>>         u16 buf_len, dword_len;
>>>>>>         s32 status;
>>>>>
>>>>> This looks bogus. An array is inline, a pointer points elsewhere -
>>>>> they're not interchangeable.
>>>>
>>>> Yep; but in this case these are the only places in the code where _u32arr_ is
>>>> being used:
>>>>
>>>> 3707         /* first pull in the header so we know the buffer length */
>>>> 3708         for (bi = 0; bi < dword_len; bi++) {
>>>> 3709                 bp->u32arr[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
>>>> 3710                 le32_to_cpus(&bp->u32arr[bi]);
>>>> 3711         }
>>>
>>> So now line 3709 means: Read a pointer from bp->u32arr (the value
>>> being read from there is not actually a valid pointer), and write to
>>> that pointer at offset `bi`. I don't see how that line could execute
>>> without crashing.
>>
>> Yeah; you're right. I see my confusion now. Apparently, there is no escape
>> from allocating heap memory to fix this issue, as I was proposing in my
>> last email.
> 
> Why? Can't you do something like this?

Yep; it seems you're right. I was thinking in terms of a flexible array. Also,
I think I needed more coffee in my system this morning and I need to stop
working after midnight. :)

I'll send a proper patch for this, shortly. I'll add your Proposed-by
and Co-developed-by tags to the changelog text.

Thanks a lot for the feedback. I really appreciate it. :)
--
Gustavo


> 
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> b/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> index 62ddb452f862..768fa124105b 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_common.c
> @@ -3677,10 +3677,8 @@ s32 ixgbe_host_interface_command(struct
> ixgbe_hw *hw, void *buffer,
>                                  bool return_data)
>  {
>         u32 hdr_size = sizeof(struct ixgbe_hic_hdr);
> -       union {
> -               struct ixgbe_hic_hdr hdr;
> -               u32 u32arr[1];
> -       } *bp = buffer;
> +       u32 *bp = buffer;
> +       struct ixgbe_hic_hdr hdr;
>         u16 buf_len, dword_len;
>         s32 status;
>         u32 bi;
> @@ -3706,12 +3704,13 @@ s32 ixgbe_host_interface_command(struct
> ixgbe_hw *hw, void *buffer,
> 
>         /* first pull in the header so we know the buffer length */
>         for (bi = 0; bi < dword_len; bi++) {
> -               bp->u32arr[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
> -               le32_to_cpus(&bp->u32arr[bi]);
> +               bp[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
> +               le32_to_cpus(&bp[bi]);
>         }
> 
>         /* If there is any thing in data position pull it in */
> -       buf_len = bp->hdr.buf_len;
> +       memcpy(&hdr, bp, sizeof(hdr));
> +       buf_len = hdr.buf_len;
>         if (!buf_len)
>                 goto rel_out;
> 
> @@ -3726,8 +3725,8 @@ s32 ixgbe_host_interface_command(struct ixgbe_hw
> *hw, void *buffer,
> 
>         /* Pull in the rest of the buffer (bi is where we left off) */
>         for (; bi <= dword_len; bi++) {
> -               bp->u32arr[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
> -               le32_to_cpus(&bp->u32arr[bi]);
> +               bp[bi] = IXGBE_READ_REG_ARRAY(hw, IXGBE_FLEX_MNG, bi);
> +               le32_to_cpus(&bp[bi]);
>         }
> 
>  rel_out:
>