kernel BUG in fou_build_udp

[Palash Oswal]

Hello,
I found the following issue using syzkaller with enriched corpus on:
HEAD commit : 0bcc4025550403ae28d2984bddacafbca0a2f112
git tree: linux

C Reproducer : https://gist.github.com/oswalpalash/2a4bdb639c605ec80dbeec220e09603c
Kernel .config :
https://gist.github.com/oswalpalash/d9580b0bfce202b37445fa5fd426e41f
syz-repro :
r0 = socket$inet6(0xa, 0x2, 0x0)
r1 = socket$nl_route(0x10, 0x3, 0x0)
r2 = socket(0x10, 0x803, 0x0)
sendmsg$nl_route(r2, &(0x7f0000000380)={0x0, 0x0,
&(0x7f0000000340)={0x0, 0x14}}, 0x0)
getsockname$packet(r2, &(0x7f0000000100)={0x11, 0x0, <r3=>0x0, 0x1,
0x0, 0x6, @broadcast}, &(0x7f00000000c0)=0x14)
sendmsg$nl_route(r1, &(0x7f0000000080)={0x0, 0x0,
&(0x7f0000000500)={&(0x7f0000000180)=@newlink={0x60, 0x10, 0x439, 0x0,
0x0, {0x0, 0x0, 0x0, 0x0, 0x9801}, [@IFLA_LINKINFO={0x40, 0x12, 0x0,
0x1, @sit={{0x8}, {0x34, 0x2, 0x0, 0x1, [@IFLA_IPTUN_LINK={0x8, 0x1,
r3}, @IFLA_IPTUN_ENCAP_TYPE={0x6, 0xf, 0x2},
@IFLA_IPTUN_ENCAP_SPORT={0x6, 0x11, 0x4e21},
@IFLA_IPTUN_ENCAP_SPORT={0x6, 0x11, 0x4e24}, @IFLA_IPTUN_LOCAL={0x8,
0x2, @dev={0xac, 0x14, 0x14, 0x16}}, @IFLA_IPTUN_ENCAP_FLAGS={0x6,
0x10, 0xfff}]}}}]}, 0x60}}, 0x20048894)
sendmmsg$inet(r0, &(0x7f00000017c0)=[{{&(0x7f0000000040)={0x2, 0x4e20,
@multicast1}, 0x10, 0x0, 0x0, &(0x7f0000000000)=[@ip_pktinfo={{0x1c,
0x0, 0x8, {r3, @empty, @remote}}}], 0x20}}], 0x1, 0x0)


Console log:

skbuff: skb_under_panic: text:ffffffff88a09da0 len:48 put:8
head:ffff88801e4be680 data:ffff88801e4be67c tail:0x2c end:0x140
dev:sit1
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:150!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 10068 Comm: syz-executor.3 Not tainted
6.3.0-rc6-pasta-00035-g0bcc40255504 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:skb_panic+0x152/0x1d0
Code: 0f b6 04 01 84 c0 74 04 3c 03 7e 20 8b 4b 70 41 56 45 89 e8 48
c7 c7 80 b3 5b 8b 41 57 56 48 89 ee 52 4c 89 e2 e8 ae 15 6c f9 <0f> 0b
4c 89 4c 24 10 48 89 54 24 08 48 89 34 24 e8 69 1f d8 f9 4c
RSP: 0018:ffffc900029bead0 EFLAGS: 00010282
RAX: 0000000000000084 RBX: ffff88801d1c3d00 RCX: ffffc9000d863000
RDX: 0000000000000000 RSI: ffffffff816695cc RDI: 0000000000000005
RBP: ffffffff8b5bc1e0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000400 R11: 0000000000000000 R12: ffffffff88a09da0
R13: 0000000000000008 R14: ffff8880306b8000 R15: 0000000000000140
FS:  00007f1dae5ed700(0000) GS:ffff888063a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000564f403b7d10 CR3: 0000000117f1c000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 skb_push+0xc8/0xe0
 fou_build_udp+0x30/0x370
 gue_build_header+0xfb/0x150
 ip_tunnel_xmit+0x66e/0x3150
 sit_tunnel_xmit__.isra.0+0xe7/0x150
 sit_tunnel_xmit+0xf7e/0x28e0
 dev_hard_start_xmit+0x187/0x700
 __dev_queue_xmit+0x2ce4/0x3c40
 neigh_connected_output+0x3c2/0x550
 ip_finish_output2+0x78a/0x22e0
 __ip_finish_output+0x396/0x650
 ip_finish_output+0x31/0x280
 ip_mc_output+0x21f/0x710
 ip_send_skb+0xd8/0x260
 udp_send_skb+0x73a/0x1480
 udp_sendmsg+0x1bb2/0x2840
 udpv6_sendmsg+0x1710/0x2c20
 inet6_sendmsg+0x9d/0xe0
 sock_sendmsg+0xde/0x190
 ____sys_sendmsg+0x334/0x900
 ___sys_sendmsg+0x110/0x1b0
 __sys_sendmmsg+0x18f/0x460
 __x64_sys_sendmmsg+0x9d/0x100
 do_syscall_64+0x39/0xb0
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f1dad88eacd
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f1dae5ecbf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f1dad9bbf80 RCX: 00007f1dad88eacd
RDX: 0000000000000001 RSI: 00000000200017c0 RDI: 0000000000000003
RBP: 00007f1dad8fcb05 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fff4922802f R14: 00007fff492281d0 R15: 00007f1dae5ecd80
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:skb_panic+0x152/0x1d0
Code: 0f b6 04 01 84 c0 74 04 3c 03 7e 20 8b 4b 70 41 56 45 89 e8 48
c7 c7 80 b3 5b 8b 41 57 56 48 89 ee 52 4c 89 e2 e8 ae 15 6c f9 <0f> 0b
4c 89 4c 24 10 48 89 54 24 08 48 89 34 24 e8 69 1f d8 f9 4c
RSP: 0018:ffffc900029bead0 EFLAGS: 00010282
RAX: 0000000000000084 RBX: ffff88801d1c3d00 RCX: ffffc9000d863000
RDX: 0000000000000000 RSI: ffffffff816695cc RDI: 0000000000000005
RBP: ffffffff8b5bc1e0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000400 R11: 0000000000000000 R12: ffffffff88a09da0
R13: 0000000000000008 R14: ffff8880306b8000 R15: 0000000000000140
FS:  00007f1dae5ed700(0000) GS:ffff888063a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000564f403b7d10 CR3: 0000000117f1c000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400