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Subject: Re: [V9fs-developer] [PATCH] p9_parse_header() validate PDU length
To:     Dominique Martinet <asmadeus@codewreck.org>
Cc:     ericvh@gmail.com, rminnich@sandia.gov, lucho@ionkov.net,
        viro@ZenIV.linux.org.uk, davem@davemloft.net,
        v9fs-developer@lists.sourceforge.net, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller@googlegroups.com,
        Andrew Morton <akpm@linux-foundation.org>
References: <20180712110211.25535-1-tomasbortoli@gmail.com>
 <20180712114304.GB17774@nautica>
From:   Tomas Bortoli <tomasbortoli@gmail.com>
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Date:   Thu, 12 Jul 2018 18:19:36 +0200
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+ Cc: Andrew Morton <akpm@linux-foundation.org>

On 07/12/2018 01:43 PM, Dominique Martinet wrote:
> Tomas Bortoli wrote on Thu, Jul 12, 2018:
>> This patch adds checks to the p9_parse_header() function to
>> verify that the length found within the header coincides with the actu=
al
>> length of the PDU. Furthermore, it checks that the length stays within=
 the
>> acceptable range. To do this the patch brings the actual length of the=
 PDU
>> from the different transport layers (rdma and virtio). For TCP (trans_=
fd.c)
>> the length is not know before, so we get it from the header but we che=
ck it
>> anyway that it's within the valid range.

Still for TCP it you could read "garbage" pre-allocated memory but I
don't know how much it is a risk, it might be a good idea to zero it
post allocation (I mean pdu->sdata). Allocated at:

https://github.com/torvalds/linux/blob/master/net/9p/client.c#L236

> Just a note on transports here, I totally had forgotten about trans_xen=

> when we discussed this earlier as it is fairly new, but it looks like i=
t
> sets the length in the fcall properly so it should work without any
> change.
>
> I however cannot test trans=3Dxen, so if someone could either point me =
to
> how to set that up (I couldn't find any decent documentation) or do som=
e
> very basic tests that would be great.

>> Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
>> Reported-by: syzbot+65c6b72f284a39d416b4@syzkaller.appspotmail.com
> Looks good to me, as the rdma/virtio part come from my suggestion:
> Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>

True
>
>> diff --git a/net/9p/trans_rdma.c b/net/9p/trans_rdma.c
>> index 3d414acb7015..002badbcc9c0 100644
>> --- a/net/9p/trans_rdma.c
>> +++ b/net/9p/trans_rdma.c
>> @@ -319,7 +319,7 @@ recv_done(struct ib_cq *cq, struct ib_wc *wc)
>> =20
>>  	if (wc->status !=3D IB_WC_SUCCESS)
>>  		goto err_out;
>> -
>> +	c->rc->size =3D wc->byte_len;
> (nitpick, I'd keep the empty line here. If you don't mind I'll add it
> back in my tree; this doesn't warrant a v2)
>

Sure,

Tomas