linux-kernel - Re: [PATCH 0/2] net/af_packet: Fix kernel BUG in __skb_gso

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Date:   Wed, 4 Jan 2023 13:43:43 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Tudor Ambarus <tudor.ambarus@...aro.org>
Cc:     stable@...r.kernel.org, willemdebruijn.kernel@...il.com,
        mst@...hat.com, jasowang@...hat.com, edumazet@...gle.com,
        virtualization@...ts.linux-foundation.org, davem@...emloft.net,
        kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
        willemb@...gle.com, syzkaller@...glegroups.com,
        liuhangbin@...il.com, linux-kernel@...r.kernel.org,
        joneslee@...gle.com
Subject: Re: [PATCH 0/2] net/af_packet: Fix kernel BUG in __skb_gso_segment

On Thu, Dec 22, 2022 at 10:35:43AM +0200, Tudor Ambarus wrote:
> The series is intended for stable@...r.kernel.org # 5.4+
> 
> Syzkaller reported the following bug on linux-5.{4, 10, 15}.y:
> https://syzkaller.appspot.com/bug?id=ce5575575f074c33ff80d104f5baee26f22e95f5
> 
> The upstream commit that introduces this bug is:
> 1ed1d5921139 ("net: skip virtio_net_hdr_set_proto if protocol already set")
> 
> Upstream fixes the bug with the following commits, one of which introduces
> new support:
> e9d3f80935b6 ("net/af_packet: make sure to pull mac header")
> dfed913e8b55 ("net/af_packet: add VLAN support for AF_PACKET SOCK_RAW GSO") 
> 
> The additional logic and risk backported seems manageable.
> 
> The blammed commit introduces a kernel BUG in __skb_gso_segment for
> AF_PACKET SOCK_RAW GSO VLAN tagged packets. What happens is that
> virtio_net_hdr_set_proto() exists early as skb->protocol is already set to
> ETH_P_ALL. Then in packet_parse_headers() skb->protocol is set to
> ETH_P_8021AD, but neither the network header position is adjusted, nor the
> mac header is pulled. Thus when we get to validate the xmit skb and enter
> skb_mac_gso_segment(), skb->mac_len has value 14, but vlan_depth gets
> updated to 18 after skb_network_protocol() is called. This causes the
> BUG_ON from __skb_pull(skb, vlan_depth) to be hit, as the mac header has
> not been pulled yet.
> 
> The fixes from upstream backported cleanly without conflicts. I updated
> the commit message of the first patch to describe the problem encountered,
> and added Cc, Fixes, Reported-by and Tested-by tags. For the second patch
> I just added Cc to stable indicating the versions to be fixed, and added
> my Tested and Signed-off-by tags.
> 
> I tested the patches on linux-5.{4, 10, 15}.y.
> 
> Eric Dumazet (1):
>   net/af_packet: make sure to pull mac header
> 
> Hangbin Liu (1):
>   net/af_packet: add VLAN support for AF_PACKET SOCK_RAW GSO
> 
>  net/packet/af_packet.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)

Now queued up, thanks.

greg k-h