[ovs-dev] [PATCH] flow: Fix using pointer to member of packed struct icmp6_hdr.

Ilya Maximets i.maximets at ovn.org
Wed Oct 9 16:54:29 UTC 2019

On 08.10.2019 18:55, William Tu wrote:
> On Tue, Oct 01, 2019 at 08:04:00PM +0300, Ilya Maximets wrote:
>> OVS has no structure definition for ICMPv6 header with additional
>> data. More precisely, it has, but this structure named as
>> 'icmp6_error_header' and only suitable to store error related
>> extended information.  'flow_compose_l4' stores additional
>> information in reserved bits by using system defined structure
>> 'icmp6_hdr', which is marked as 'packed' and this leads to
>> build failure with gcc >= 9:
>>    lib/flow.c:3041:34: error:
>>      taking address of packed member of 'struct icmp6_hdr' may result
>>      in an unaligned pointer value [-Werror=address-of-packed-member]
>>          uint32_t *reserved = &icmp->icmp6_dataun.icmp6_un_data32[0];
>>                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Fix that by renaming 'icmp6_error_header' to 'icmp6_data_header'
>> and allowing it to store not only errors, but any type of additional
>> information by analogue with 'struct icmp6_hdr'.
>> All the usages of 'struct icmp6_hdr' replaced with this new structure.
>> Removed redundant conversions between network and host representations.
>> Now fields are always in be.
>> This also, probably, makes flow_compose_l4 more robust by avoiding
>> possible unaligned accesses to 32 bit value.
>> Fixes: 9b2b84973db7 ("Support for match & set ICMPv6 reserved and options type fields")
>> Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
> Looks good to me! Thanks.
> Tested on travis and cirrus.
> Acked-by: William Tu <u9012063 at gmail.com>

Thanks, William!

Ben, could you, please, take a look at this too?

I just want to be sure that this change is aligned with
expectations from the network header structures in OVS.

Best regards, Ilya Maximets.

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