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Re: [Xen-devel] [PATCH] libxl: make sure buffer is null-terminated in libxl_read_file_contents
- To: Robin Lee <robinlee.sysu@xxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 27 Jun 2018 12:18:02 +0100
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, ian.jackson@xxxxxxxxxxxxx
- Delivery-date: Wed, 27 Jun 2018 11:18:16 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 27/06/18 12:08, Robin Lee wrote:
> On Wed, Jun 27, 2018 at 6:58 PM, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
>> On Wed, Jun 27, 2018 at 09:13:11AM +0000, Robin Lee wrote:
>>> On XenServer 7.1.1, we start a vm with XAPI but attach a block device with
>>> xl.
>>> We create an empty json config for the vm with the content "{}\n" and then
>>> run 'xl block-attach':
>>>
>>> # xl block-attach 1 phy:/dev/loop0 xvdz w
>>> libxl: error: libxl_json.c:950:libxl__json_parse: yajl error: parse
>>> error: trailing garbage
>>> {} K]
>>> (right here) ------^
>>>
>>> libxl: error: libxl_json.c:1053:libxl__object_from_json: unable to
>>> generate libxl__json_object from JSON representation of libxl_domain_config.
>>> libxl: error: libxl.c:1995:device_addrm_aocomplete: unable to add device
>>> libxl_device_disk_add failed.
>>>
>>> After investigation, we found the buffer returned from
>>> libxl_read_file_contents
>>> is not null-terminated. But later in libxl__object_from_json, the buffer is
>>> expected to
>>> be null-terminated. So parsing may exceeded the end of file and get in to
>>> uninisialized
>>> momery area.
>>>
>>> Signed-off-by: Robin Lee <robinlee.sysu@xxxxxxxxx>
>> I can't seem to be able to reproduce this in upstream xen. Which version
>> of Xen does XenServer 7.1.1 have? You can get that from the output of
>> `xl info` -- look for xen_{major, minor, extra}.
> I also met a strange case. We didn't see this problem with Xen 4.7.1
> that released with
> XenServer 7.1.1. But since a recently hotfix from XenServer that upgraded Xen
> to
> 4.7.4, this problem then shows up.
A later hotfix even than that will bump to 4.7.5. (This is the
Spectre/Meltdown mitigations.)
XenServer has no interesting patches to libxl/xl, so this looks like it
may have been a regression which was backported into the stable trees.
~Andrew
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