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Date: Wed, 24 Apr 2024 15:12:35 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>, Dong Chenchen <dongchenchen2@...wei.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Jiri Benc <jbenc@...hat.com>,
Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org,
syzbot+42a0dc856239de4de60e@...kaller.appspotmail.com,
syzbot+c298c9f0e46a3c86332b@...kaller.appspotmail.com
Subject: Re: [PATCH v2 net] nsh: Restore skb->{protocol,data,mac_header} for
outer header in nsh_gso_segment().
On Wed, Apr 24, 2024 at 4:36 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> syzbot triggered various splats (see [0] and links) by a crafted GSO
> packet of VIRTIO_NET_HDR_GSO_UDP layering the following protocols:
>
> ETH_P_8021AD + ETH_P_NSH + ETH_P_IPV6 + IPPROTO_UDP
>
> NSH can encapsulate IPv4, IPv6, Ethernet, NSH, and MPLS. As the inner
> protocol can be Ethernet, NSH GSO handler, nsh_gso_segment(), calls
> skb_mac_gso_segment() to invoke inner protocol GSO handlers.
>
> nsh_gso_segment() does the following for the original skb before
> calling skb_mac_gso_segment()
>
> 1. reset skb->network_header
> 2. save the original skb->{mac_heaeder,mac_len} in a local variable
> 3. pull the NSH header
> 4. resets skb->mac_header
> 5. set up skb->mac_len and skb->protocol for the inner protocol.
>
> and does the following for the segmented skb
>
> 6. set ntohs(ETH_P_NSH) to skb->protocol
> 7. push the NSH header
> 8. restore skb->mac_header
> 9. set skb->mac_header + mac_len to skb->network_header
> 10. restore skb->mac_len
>
> There are two problems in 6-7 and 8-9.
>
> (a)
> After 6 & 7, skb->data points to the NSH header, so the outer header
> (ETH_P_8021AD in this case) is stripped when skb is sent out of netdev.
>
> Also, if NSH is encapsulated by NSH + Ethernet (so NSH-Ethernet-NSH),
> skb_pull() in the first nsh_gso_segment() will make skb->data point
> to the middle of the outer NSH or Ethernet header because the Ethernet
> header is not pulled by the second nsh_gso_segment().
>
> (b)
> While restoring skb->{mac_header,network_header} in 8 & 9,
> nsh_gso_segment() does not assume that the data in the linear
> buffer is shifted.
>
> However, udp6_ufo_fragment() could shift the data and change
> skb->mac_header accordingly as demonstrated by syzbot.
>
> If this happens, even the restored skb->mac_header points to
> the middle of the outer header.
>
> It seems nsh_gso_segment() has never worked with outer headers so far.
>
> At the end of nsh_gso_segment(), the outer header must be restored for
> the segmented skb, instead of the NSH header.
>
> To do that, let's calculate the outer header position relatively from
> the inner header and set skb->{data,mac_header,protocol} properly.
>
> [0]:
> BUG: KMSAN: uninit-value in ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:524 [inline]
> BUG: KMSAN: uninit-value in ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:602 [inline]
> BUG: KMSAN: uninit-value in ipvlan_queue_xmit+0xf44/0x16b0 drivers/net/ipvlan/ipvlan_core.c:668
> ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:524 [inline]
> ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:602 [inline]
> ipvlan_queue_xmit+0xf44/0x16b0 drivers/net/ipvlan/ipvlan_core.c:668
> ipvlan_start_xmit+0x5c/0x1a0 drivers/net/ipvlan/ipvlan_main.c:222
> __netdev_start_xmit include/linux/netdevice.h:4989 [inline]
> netdev_start_xmit include/linux/netdevice.h:5003 [inline]
> xmit_one net/core/dev.c:3547 [inline]
> dev_hard_start_xmit+0x244/0xa10 net/core/dev.c:3563
> __dev_queue_xmit+0x33ed/0x51c0 net/core/dev.c:4351
> dev_queue_xmit include/linux/netdevice.h:3171 [inline]
> packet_xmit+0x9c/0x6b0 net/packet/af_packet.c:276
> packet_snd net/packet/af_packet.c:3081 [inline]
> packet_sendmsg+0x8aef/0x9f10 net/packet/af_packet.c:3113
> sock_sendmsg_nosec net/socket.c:730 [inline]
> __sock_sendmsg net/socket.c:745 [inline]
> __sys_sendto+0x735/0xa10 net/socket.c:2191
> __do_sys_sendto net/socket.c:2203 [inline]
> __se_sys_sendto net/socket.c:2199 [inline]
> __x64_sys_sendto+0x125/0x1c0 net/socket.c:2199
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x63/0x6b
>
> Uninit was created at:
> slab_post_alloc_hook mm/slub.c:3819 [inline]
> slab_alloc_node mm/slub.c:3860 [inline]
> __do_kmalloc_node mm/slub.c:3980 [inline]
> __kmalloc_node_track_caller+0x705/0x1000 mm/slub.c:4001
> kmalloc_reserve+0x249/0x4a0 net/core/skbuff.c:582
> __alloc_skb+0x352/0x790 net/core/skbuff.c:651
> skb_segment+0x20aa/0x7080 net/core/skbuff.c:4647
> udp6_ufo_fragment+0xcab/0x1150 net/ipv6/udp_offload.c:109
> ipv6_gso_segment+0x14be/0x2ca0 net/ipv6/ip6_offload.c:152
> skb_mac_gso_segment+0x3e8/0x760 net/core/gso.c:53
> nsh_gso_segment+0x6f4/0xf70 net/nsh/nsh.c:108
> skb_mac_gso_segment+0x3e8/0x760 net/core/gso.c:53
> __skb_gso_segment+0x4b0/0x730 net/core/gso.c:124
> skb_gso_segment include/net/gso.h:83 [inline]
> validate_xmit_skb+0x107f/0x1930 net/core/dev.c:3628
> __dev_queue_xmit+0x1f28/0x51c0 net/core/dev.c:4343
> dev_queue_xmit include/linux/netdevice.h:3171 [inline]
> packet_xmit+0x9c/0x6b0 net/packet/af_packet.c:276
> packet_snd net/packet/af_packet.c:3081 [inline]
> packet_sendmsg+0x8aef/0x9f10 net/packet/af_packet.c:3113
> sock_sendmsg_nosec net/socket.c:730 [inline]
> __sock_sendmsg net/socket.c:745 [inline]
> __sys_sendto+0x735/0xa10 net/socket.c:2191
> __do_sys_sendto net/socket.c:2203 [inline]
> __se_sys_sendto net/socket.c:2199 [inline]
> __x64_sys_sendto+0x125/0x1c0 net/socket.c:2199
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x63/0x6b
>
> CPU: 1 PID: 5101 Comm: syz-executor421 Not tainted 6.8.0-rc5-syzkaller-00297-gf2e367d6ad3b #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
>
> Fixes: c411ed854584 ("nsh: add GSO support")
> Reported-and-tested-by: syzbot+42a0dc856239de4de60e@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=42a0dc856239de4de60e
> Reported-and-tested-by: syzbot+c298c9f0e46a3c86332b@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=c298c9f0e46a3c86332b
> Link: https://lore.kernel.org/netdev/20240415222041.18537-1-kuniyu@amazon.com/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
> v2: Fix issue in the NSH side
> v1: https://lore.kernel.org/netdev/20240415222041.18537-1-kuniyu@amazon.com/
> ---
> net/nsh/nsh.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/net/nsh/nsh.c b/net/nsh/nsh.c
> index f4a38bd6a7e0..bfb7758063f3 100644
> --- a/net/nsh/nsh.c
> +++ b/net/nsh/nsh.c
> @@ -77,13 +77,15 @@ EXPORT_SYMBOL_GPL(nsh_pop);
> static struct sk_buff *nsh_gso_segment(struct sk_buff *skb,
> netdev_features_t features)
> {
> + unsigned int outer_hlen, mac_len, nsh_len;
> struct sk_buff *segs = ERR_PTR(-EINVAL);
> u16 mac_offset = skb->mac_header;
> - unsigned int nsh_len, mac_len;
> - __be16 proto;
> + __be16 outer_proto, proto;
>
> skb_reset_network_header(skb);
>
> + outer_proto = skb->protocol;
> + outer_hlen = skb_mac_header_len(skb);
> mac_len = skb->mac_len;
>
> if (unlikely(!pskb_may_pull(skb, NSH_BASE_HDR_LEN)))
> @@ -113,10 +115,10 @@ static struct sk_buff *nsh_gso_segment(struct sk_buff *skb,
> }
>
> for (skb = segs; skb; skb = skb->next) {
> - skb->protocol = htons(ETH_P_NSH);
> - __skb_push(skb, nsh_len);
> - skb->mac_header = mac_offset;
> - skb->network_header = skb->mac_header + mac_len;
> + skb->protocol = outer_proto;
> + __skb_push(skb, nsh_len + outer_hlen);
> + skb_reset_mac_header(skb);
> + skb_set_network_header(skb, outer_hlen);
> skb->mac_len = mac_len;
> }
>
Lets Cc Dong Chenchen <dongchenchen2@...wei.com>
Prior work here was :
commit c83b49383b595be50647f0c764a48c78b5f3c4f8
Author: Dong Chenchen <dongchenchen2@...wei.com>
Date: Thu May 11 20:54:40 2023 +0800
net: nsh: Use correct mac_offset to unwind gso skb in nsh_gso_segment()
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