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Message-ID: <6889005c9d7f1_1669652947@willemb.c.googlers.com.notmuch>
Date: Tue, 29 Jul 2025 13:09:48 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Wang Liang <wangliang74@...wei.com>,
willemdebruijn.kernel@...il.com,
davem@...emloft.net,
edumazet@...gle.com,
kuba@...nel.org,
pabeni@...hat.com,
horms@...nel.org,
atenart@...nel.org
Cc: yuehaibing@...wei.com,
zhangchangzhong@...wei.com,
wangliang74@...wei.com,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net v2] net: drop gso udp packets in udp_rcv_segment()
Can limit to drop UFO packets, as other GSO packets will get segmented
correctly.
Wang Liang wrote:
> When sending a packet with virtio_net_hdr to tun device, if the gso_type
> in virtio_net_hdr is SKB_GSO_UDP and the gso_size is less than udphdr
> size, below crash may happen.
>
> ------------[ cut here ]------------
> kernel BUG at net/core/skbuff.c:4572!
> Oops: invalid opcode: 0000 [#1] SMP NOPTI
> CPU: 0 UID: 0 PID: 62 Comm: mytest Not tainted 6.16.0-rc7 #203 PREEMPT(voluntary)
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> RIP: 0010:skb_pull_rcsum+0x8e/0xa0
> Code: 00 00 5b c3 cc cc cc cc 8b 93 88 00 00 00 f7 da e8 37 44 38 00 f7 d8 89 83 88 00 00 00 48 8b 83 c8 00 00 00 5b c3 cc cc cc cc <0f> 0b 0f 0b 66 66 2e 0f 1f 84 00 000
> RSP: 0018:ffffc900001fba38 EFLAGS: 00000297
> RAX: 0000000000000004 RBX: ffff8880040c1000 RCX: ffffc900001fb948
> RDX: ffff888003e6d700 RSI: 0000000000000008 RDI: ffff88800411a062
> RBP: ffff8880040c1000 R08: 0000000000000000 R09: 0000000000000001
> R10: ffff888003606c00 R11: 0000000000000001 R12: 0000000000000000
> R13: ffff888004060900 R14: ffff888004050000 R15: ffff888004060900
> FS: 000000002406d3c0(0000) GS:ffff888084a19000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000040 CR3: 0000000004007000 CR4: 00000000000006f0
> Call Trace:
> <TASK>
> udp_queue_rcv_one_skb+0x176/0x4b0 net/ipv4/udp.c:2445
> udp_queue_rcv_skb+0x155/0x1f0 net/ipv4/udp.c:2475
> udp_unicast_rcv_skb+0x71/0x90 net/ipv4/udp.c:2626
> __udp4_lib_rcv+0x433/0xb00 net/ipv4/udp.c:2690
> ip_protocol_deliver_rcu+0xa6/0x160 net/ipv4/ip_input.c:205
> ip_local_deliver_finish+0x72/0x90 net/ipv4/ip_input.c:233
> ip_sublist_rcv_finish+0x5f/0x70 net/ipv4/ip_input.c:579
> ip_sublist_rcv+0x122/0x1b0 net/ipv4/ip_input.c:636
> ip_list_rcv+0xf7/0x130 net/ipv4/ip_input.c:670
> __netif_receive_skb_list_core+0x21d/0x240 net/core/dev.c:6067
> netif_receive_skb_list_internal+0x186/0x2b0 net/core/dev.c:6210
> napi_complete_done+0x78/0x180 net/core/dev.c:6580
> tun_get_user+0xa63/0x1120 drivers/net/tun.c:1909
> tun_chr_write_iter+0x65/0xb0 drivers/net/tun.c:1984
> vfs_write+0x300/0x420 fs/read_write.c:593
> ksys_write+0x60/0xd0 fs/read_write.c:686
> do_syscall_64+0x50/0x1c0 arch/x86/entry/syscall_64.c:63
> </TASK>
>
> To trigger gso segment in udp_queue_rcv_skb(), we should also set option
> UDP_ENCAP_ESPINUDP to enable udp_sk(sk)->encap_rcv. When the encap_rcv
> hook return 1 in udp_queue_rcv_one_skb(), udp_csum_pull_header() will try
> to pull udphdr, but the skb size has been segmented to gso size, which
> leads to this crash.
>
> Previous commit cf329aa42b66 ("udp: cope with UDP GRO packet misdirection")
> introduces segmentation in UDP receive path only for GRO, which was never
> intended to be used for UFO, so drop gso udp packets in udp_rcv_segment().
>
> Fixes: cf329aa42b66 ("udp: cope with UDP GRO packet misdirection")
> Fixes: 3d010c8031e3 ("udp: do not accept non-tunnel GSO skbs landing in a tunnel")
Only one Fixes tag, to know where to backport too.
The segmentation on receive is introduced in the first commit. I'd
keep only that.
And please add a Link: to the email thread with the analysis of the
bug, your v1 (above the ---).
> Suggested-by: Willem de Bruijn <willemdebruijn.kernel@...il.com>
> Signed-off-by: Wang Liang <wangliang74@...wei.com>
> ---
> v1: https://lore.kernel.org/netdev/20250724083005.3918375-1-wangliang74@huawei.com/
> v2: Drop ufo packets instead of checking min gso size.
> ---
> include/net/udp.h | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/include/net/udp.h b/include/net/udp.h
> index a772510b2aa5..e3fcda71f6c1 100644
> --- a/include/net/udp.h
> +++ b/include/net/udp.h
> @@ -587,6 +587,14 @@ static inline struct sk_buff *udp_rcv_segment(struct sock *sk,
> {
> netdev_features_t features = NETIF_F_SG;
> struct sk_buff *segs;
> + int drop_count = 1;
This is rare, can move initialization into the branch.
> +
> + /*
> + * Segmentation in UDP receive path is only for UDP GRO, drop udp
> + * fragmentation offload (UFO) packets.
> + */
> + if (skb_shinfo(skb)->gso_type & (SKB_GSO_UDP | SKB_GSO_UDP_L4))
Only SKB_GSO_UDP.
The purpose of this function is to correctly segment SKB_GSO_UDP_L4
packets.
> + goto drop;
>
> /* Avoid csum recalculation by skb_segment unless userspace explicitly
> * asks for the final checksum values
> @@ -610,16 +618,18 @@ static inline struct sk_buff *udp_rcv_segment(struct sock *sk,
> */
> segs = __skb_gso_segment(skb, features, false);
> if (IS_ERR_OR_NULL(segs)) {
> - int segs_nr = skb_shinfo(skb)->gso_segs;
> -
> - atomic_add(segs_nr, &sk->sk_drops);
> - SNMP_ADD_STATS(__UDPX_MIB(sk, ipv4), UDP_MIB_INERRORS, segs_nr);
> - kfree_skb(skb);
> - return NULL;
> + drop_count = skb_shinfo(skb)->gso_segs;
> + goto drop;
> }
>
> consume_skb(skb);
> return segs;
> +
> +drop:
> + atomic_add(drop_count, &sk->sk_drops);
> + SNMP_ADD_STATS(__UDPX_MIB(sk, ipv4), UDP_MIB_INERRORS, drop_count);
> + kfree_skb(skb);
> + return NULL;
> }
>
> static inline void udp_post_segment_fix_csum(struct sk_buff *skb)
> --
> 2.34.1
>
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