CVE-2025-38622

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

net: drop UFO packets in udprcvsegment()

When sending a packet with virtionethdr to tun device, if the gsotype in virtionethdr is SKBGSOUDP and the gsosize 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:skbpullrcsum+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> udpqueuercvoneskb+0x176/0x4b0 net/ipv4/udp.c:2445 udpqueuercvskb+0x155/0x1f0 net/ipv4/udp.c:2475 udpunicastrcvskb+0x71/0x90 net/ipv4/udp.c:2626 __udp4librcv+0x433/0xb00 net/ipv4/udp.c:2690 ipprotocoldeliverrcu+0xa6/0x160 net/ipv4/ipinput.c:205 iplocaldeliverfinish+0x72/0x90 net/ipv4/ipinput.c:233 ipsublistrcvfinish+0x5f/0x70 net/ipv4/ipinput.c:579 ipsublistrcv+0x122/0x1b0 net/ipv4/ipinput.c:636 iplistrcv+0xf7/0x130 net/ipv4/ipinput.c:670 __netifreceiveskblistcore+0x21d/0x240 net/core/dev.c:6067 netifreceiveskblistinternal+0x186/0x2b0 net/core/dev.c:6210 napicompletedone+0x78/0x180 net/core/dev.c:6580 tungetuser+0xa63/0x1120 drivers/net/tun.c:1909 tunchrwriteiter+0x65/0xb0 drivers/net/tun.c:1984 vfswrite+0x300/0x420 fs/readwrite.c:593 ksyswrite+0x60/0xd0 fs/readwrite.c:686 dosyscall64+0x50/0x1c0 arch/x86/entry/syscall64.c:63 </TASK>

To trigger gso segment in udpqueuercvskb(), we should also set option UDPENCAPESPINUDP to enable udpsk(sk)->encaprcv. When the encaprcv hook return 1 in udpqueuercvoneskb(), udpcsumpull_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 udprcvsegment().