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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
References: <20180712110211.25535-1-tomasbortoli@gmail.com>
 <20180718051321.GB16605@nautica>
From:   Tomas Bortoli <tomasbortoli@gmail.com>
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Message-ID: <8c25c95f-a8cc-9530-b0e7-93bb5af8888d@gmail.com>
Date:   Wed, 18 Jul 2018 10:39:51 +0200
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On 07/18/2018 07:13 AM, 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 actual
>> 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 check it
>> anyway that it's within the valid range.
>>
>> Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
>> Reported-by: syzbot+65c6b72f284a39d416b4@syzkaller.appspotmail.com
>> ---
>> [..]
>> @@ -498,6 +489,21 @@ p9_parse_header(struct p9_fcall *pdu, int32_t *size, int8_t *type, int16_t *tag,
>>  	if (size)
>>  		*size = r_size;
>>  
>> +	if (pdu->size != r_size) {
>> +		err = -EINVAL;
>> +		goto rewind_and_exit;
>> +	}
>> +	if (pdu->size >= pdu->capacity || pdu->size < 7) {
>> +		p9_debug(P9_DEBUG_ERROR,
>> +			 "requested packet size too big or too small: %d\n",
>> +			 pdu->size);
>> +		return -EIO;
>> +	}
> Actually, I've been bad advice - this breaks on virtio with zc packets -
> a read or ls in a big directory fails with this in dmesg
> [ 1006.853775] 9pnet: -- p9_parse_header (17123): requested packet size too big or too small: 4306
> [ 1006.853780] 9pnet: -- p9_check_zc_errors (17123): couldn't parse header -5
>
> I haven't given this any thought yet, but dropping the patch for now
>
It seems that pdu->capacity is set to less than 4306 at that point, we
can just increase it.