From: piaojun <piaojun@huawei.com>
To: Tomas Bortoli <tomasbortoli@gmail.com>, <ericvh@gmail.com>,
<rminnich@sandia.gov>, <lucho@ionkov.net>
Cc: <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<syzkaller@googlegroups.com>,
<v9fs-developer@lists.sourceforge.net>, <davem@davemloft.net>
Subject: Re: [V9fs-developer] [PATCH] Integer underflow in pdu_read()
Date: Tue, 10 Jul 2018 19:06:17 +0800 [thread overview]
Message-ID: <5B449329.1050507@huawei.com> (raw)
In-Reply-To: <36523cc7-adec-9e61-d34c-dc00806c403a@gmail.com>
Hi Tomas,
Thanks for your explaination, and I get your point.
On 2018/7/10 16:27, Tomas Bortoli wrote:
> Hi Jun,
>
> Intuitively, if you have a packet of size x and you read at an offset y,
> when y>x you are off the packet. That's an out out bound read.
>
> In this specific code when offset > size, the available length
> estimation will fail as there will be an underflow resulting from
> offset-size (it'll give a big big number) that breaks the out-of-bound
> control put in place (if offset-size is a big big number, the asked size
> to read will be probably smaller and therefore allowed).
>
> These definitions might help:
> https://cwe.mitre.org/data/definitions/787.html
> https://cwe.mitre.org/data/definitions/125.html
>
> Tomas
>> Hi Tomas,
>>
>> It looks like pdu->size should always be greater than pdu->offset, right?
>> My question may be very easy for you, please help explaining.
>>
>> Thanks,
>> Jun
>>
>> On 2018/7/10 3:26, Tomas Bortoli wrote:
>>> The pdu_read() function suffers from an integer underflow.
>>> When pdu->offset is greater than pdu->size, the length calculation will have
>>> a wrong result, resulting in an out-of-bound read.
>>> This patch modifies also pdu_write() in the same way to prevent the same
>>> issue from happening there and for consistency.
>>>
>>> Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
>>> Reported-by: syzbot+65c6b72f284a39d416b4@syzkaller.appspotmail.com
>>> ---
>>> net/9p/protocol.c | 12 ++++++++----
>>> 1 file changed, 8 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/net/9p/protocol.c b/net/9p/protocol.c
>>> index 931ea00c4fed..f1e2425f920b 100644
>>> --- a/net/9p/protocol.c
>>> +++ b/net/9p/protocol.c
>>> @@ -55,16 +55,20 @@ EXPORT_SYMBOL(p9stat_free);
>>>
>>> size_t pdu_read(struct p9_fcall *pdu, void *data, size_t size)
>>> {
>>> - size_t len = min(pdu->size - pdu->offset, size);
>>> - memcpy(data, &pdu->sdata[pdu->offset], len);
>>> + size_t len = pdu->offset > pdu->size ? 0 :
>>> + min(pdu->size - pdu->offset, size);
>>> + if (len != 0)
>>> + memcpy(data, &pdu->sdata[pdu->offset], len);
>>> pdu->offset += len;
>>> return size - len;
>>> }
>>>
>>> static size_t pdu_write(struct p9_fcall *pdu, const void *data, size_t size)
>>> {
>>> - size_t len = min(pdu->capacity - pdu->size, size);
>>> - memcpy(&pdu->sdata[pdu->size], data, len);
>>> + size_t len = pdu->size > pdu->capacity ? 0 :
>>> + min(pdu->capacity - pdu->size, size);
>>> + if (len != 0)
>>> + memcpy(&pdu->sdata[pdu->size], data, len);
>>> pdu->size += len;
>>> return size - len;
>>> }
>>>
>
>
>
next prev parent reply other threads:[~2018-07-10 11:06 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-09 19:26 [V9fs-developer] [PATCH] Integer underflow in pdu_read() Tomas Bortoli
2018-07-09 19:31 ` Al Viro
2018-07-09 22:14 ` Tomas Bortoli
2018-07-09 23:29 ` Dominique Martinet
2018-07-10 1:27 ` piaojun
2018-07-10 8:27 ` Tomas Bortoli
2018-07-10 11:06 ` piaojun [this message]
2018-07-10 11:16 ` piaojun
2018-07-11 2:04 ` jiangyiwen
2018-07-12 11:05 ` Tomas Bortoli
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