On Wed, Jan 17, 2018 at 10:48 PM, Jason Wang <[email protected]> wrote:
>
>
> On 2018年01月18日 07:11, Willem de Bruijn wrote:
>>
>> From: Willem de Bruijn<[email protected]>
>>
>> Validate gso_type of untrusted SKB_GSO_DODGY packets during
>> segmentation.
>>
>> Untrusted user packets are limited to a small set of gso types in
>> virtio_net_hdr_to_skb. But segmentation occurs on packet contents.
>> Syzkaller was able to enter gso callbacks that are not hardened
>> against untrusted user input.
>>
>> Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")
>
>
> This commit is suspicious, I guess it should be 5c7cdf339af5 ("gso: Remove
> arbitrary checks for unsupported GSO")
The specific SCTP path was introduced with commit 90017accff61 ("sctp:
add GSO support"). But the main issue that packets can be delivered to
gso handlers different from their gso_type goes back further.
The commit you reference is actually older than the sctp gso patch, so
it makes sense that it did not have a check in the sctp_gso_segment.
I still think that we should check in inet_gso_segment when we have
the proto, instead of in each {tcp, sctp, udp, esp, ...} handler having
a check of the form.
!(type & (SKB_GSO_TCPV4 |
SKB_GSO_TCPV6))))
Note that the above commit also only had these checks in the TSO
branch
if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST)) {
but the case where this condition fails has to be protected just as
well, so a revert of that patch + new tests in all handlers added
since is not sufficient.
>> Link:http://lkml.kernel.org/r/<[email protected]>
>> Reported-by:[email protected]
>> Signed-off-by: Willem de Bruijn<[email protected]>
>> ---
>> net/ipv4/af_inet.c | 21 +++++++++++++++++++++
>> net/ipv6/ip6_offload.c | 23 ++++++++++++++++++++++-
>> 2 files changed, 43 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
>> index f00499a46927..d5a36827f7b1 100644
>> --- a/net/ipv4/af_inet.c
>> +++ b/net/ipv4/af_inet.c
>> @@ -1220,6 +1220,25 @@ int inet_sk_rebuild_header(struct sock *sk)
>> }
>> EXPORT_SYMBOL(inet_sk_rebuild_header);
>> +static bool inet_gso_validate_dodgy(struct sk_buff *skb, int ipproto)
>> +{
>> + unsigned int gso_type = skb_shinfo(skb)->gso_type;
>> +
>> + if (gso_type & SKB_GSO_DODGY) {
>> + switch (gso_type & ~SKB_GSO_DODGY) {
>> + case SKB_GSO_TCPV4:
>> + case SKB_GSO_TCPV4 | SKB_GSO_TCP_ECN:
>> + return ipproto == IPPROTO_TCP;
>> + case SKB_GSO_UDP:
>> + return ipproto == IPPROTO_UDP;
>> + default:
>> + return false;
>> + }
>> + }
>> +
>> + return true;
>> +}
>
>
> This seems more strict than what was removed by 5c7cdf339af5. Any reason for
> this? I'm asking since this probably work for virito-net but I'm not sure it
> works for other sources.
All sources are limited to the same VIRTIO_NET_HDR_GSO_.. types that
virtio_net_hdr_to_skb supports, as far as I know.
