net: drop UFO packets in udp_rcv_segment()

In the Linux kernel, the following vulnerability has been resolved:

net: drop UFO packets in udp_rcv_segment()

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 UFO packets in udp_rcv_segment().