fou, fou6: avoid uninit-value in gue_err() and gue6_err()

fou, fou6: avoid uninit-value in gue_err() and gue6_err()

My prior commit missed the fact that these functions
were using udp_hdr() (aka skb_transport_header())
to get access to GUE header.

Since pskb_transport_may_pull() does not exist yet, we have to add
transport_offset to our pskb_may_pull() calls.

BUG: KMSAN: uninit-value in gue_err+0x514/0xfa0 net/ipv4/fou.c:1032
CPU: 1 PID: 10648 Comm: syz-executor.1 Not tainted 5.0.0+ #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x173/0x1d0 lib/dump_stack.c:113
 kmsan_report+0x12e/0x2a0 mm/kmsan/kmsan.c:600
 __msan_warning+0x82/0xf0 mm/kmsan/kmsan_instr.c:313
 gue_err+0x514/0xfa0 net/ipv4/fou.c:1032
 __udp4_lib_err_encap_no_sk net/ipv4/udp.c:571 [inline]
 __udp4_lib_err_encap net/ipv4/udp.c:626 [inline]
 __udp4_lib_err+0x12e6/0x1d40 net/ipv4/udp.c:665
 udp_err+0x74/0x90 net/ipv4/udp.c:737
 icmp_socket_deliver net/ipv4/icmp.c:767 [inline]
 icmp_unreach+0xb65/0x1070 net/ipv4/icmp.c:884
 icmp_rcv+0x11a1/0x1950 net/ipv4/icmp.c:1066
 ip_protocol_deliver_rcu+0x584/0xbb0 net/ipv4/ip_input.c:208
 ip_local_deliver_finish net/ipv4/ip_input.c:234 [inline]
 NF_HOOK include/linux/netfilter.h:289 [inline]
 ip_local_deliver+0x624/0x7b0 net/ipv4/ip_input.c:255
 dst_input include/net/dst.h:450 [inline]
 ip_rcv_finish net/ipv4/ip_input.c:414 [inline]
 NF_HOOK include/linux/netfilter.h:289 [inline]
 ip_rcv+0x6bd/0x740 net/ipv4/ip_input.c:524
 __netif_receive_skb_one_core net/core/dev.c:4973 [inline]
 __netif_receive_skb net/core/dev.c:5083 [inline]
 process_backlog+0x756/0x10e0 net/core/dev.c:5923
 napi_poll net/core/dev.c:6346 [inline]
 net_rx_action+0x78b/0x1a60 net/core/dev.c:6412
 __do_softirq+0x53f/0x93a kernel/softirq.c:293
 invoke_softirq kernel/softirq.c:375 [inline]
 irq_exit+0x214/0x250 kernel/softirq.c:416
 exiting_irq+0xe/0x10 arch/x86/include/asm/apic.h:536
 smp_apic_timer_interrupt+0x48/0x70 arch/x86/kernel/apic/apic.c:1064
 apic_timer_interrupt+0x2e/0x40 arch/x86/entry/entry_64.S:814
 </IRQ>
RIP: 0010:finish_lock_switch+0x2b/0x40 kernel/sched/core.c:2597
Code: 48 89 e5 53 48 89 fb e8 63 e7 95 00 8b b8 88 0c 00 00 48 8b 00 48 85 c0 75 12 48 89 df e8 dd db 95 00 c6 00 00 c6 03 00 fb 5b <5d> c3 e8 4e e6 95 00 eb e7 66 90 66 2e 0f 1f 84 00 00 00 00 00 55
RSP: 0018:ffff888081a0fc80 EFLAGS: 00000296 ORIG_RAX: ffffffffffffff13
RAX: ffff88821fd6bd80 RBX: ffff888027898000 RCX: ccccccccccccd000
RDX: ffff88821fca8d80 RSI: ffff888000000000 RDI: 00000000000004a0
RBP: ffff888081a0fc80 R08: 0000000000000002 R09: ffff888081a0fb08
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: ffff88811130e388 R14: ffff88811130da00 R15: ffff88812fdb7d80
 finish_task_switch+0xfc/0x2d0 kernel/sched/core.c:2698
 context_switch kernel/sched/core.c:2851 [inline]
 __schedule+0x6cc/0x800 kernel/sched/core.c:3491
 schedule+0x15b/0x240 kernel/sched/core.c:3535
 freezable_schedule include/linux/freezer.h:172 [inline]
 do_nanosleep+0x2ba/0x980 kernel/time/hrtimer.c:1679
 hrtimer_nanosleep kernel/time/hrtimer.c:1733 [inline]
 __do_sys_nanosleep kernel/time/hrtimer.c:1767 [inline]
 __se_sys_nanosleep+0x746/0x960 kernel/time/hrtimer.c:1754
 __x64_sys_nanosleep+0x3e/0x60 kernel/time/hrtimer.c:1754
 do_syscall_64+0xbc/0xf0 arch/x86/entry/common.c:291
 entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x4855a0
Code: 00 00 48 c7 c0 d4 ff ff ff 64 c7 00 16 00 00 00 31 c0 eb be 66 0f 1f 44 00 00 83 3d b1 11 5d 00 00 75 14 b8 23 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 04 e2 f8 ff c3 48 83 ec 08 e8 3a 55 fd ff
RSP: 002b:0000000000a4fd58 EFLAGS: 00000246 ORIG_RAX: 0000000000000023
RAX: ffffffffffffffda RBX: 0000000000085780 RCX: 00000000004855a0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000a4fd60
RBP: 00000000000007ec R08: 0000000000000001 R09: 0000000000ceb940
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000008
R13: 0000000000a4fdb0 R14: 0000000000085711 R15: 0000000000a4fdc0

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:205 [inline]
 kmsan_internal_poison_shadow+0x92/0x150 mm/kmsan/kmsan.c:159
 kmsan_kmalloc+0xa6/0x130 mm/kmsan/kmsan_hooks.c:176
 kmsan_slab_alloc+0xe/0x10 mm/kmsan/kmsan_hooks.c:185
 slab_post_alloc_hook mm/slab.h:445 [inline]
 slab_alloc_node mm/slub.c:2773 [inline]
 __kmalloc_node_track_caller+0xe9e/0xff0 mm/slub.c:4398
 __kmalloc_reserve net/core/skbuff.c:140 [inline]
 __alloc_skb+0x309/0xa20 net/core/skbuff.c:208
 alloc_skb include/linux/skbuff.h:1012 [inline]
 alloc_skb_with_frags+0x186/0xa60 net/core/skbuff.c:5287
 sock_alloc_send_pskb+0xafd/0x10a0 net/core/sock.c:2091
 sock_alloc_send_skb+0xca/0xe0 net/core/sock.c:2108
 __ip_append_data+0x34cd/0x5000 net/ipv4/ip_output.c:998
 ip_append_data+0x324/0x480 net/ipv4/ip_output.c:1220
 icmp_push_reply+0x23d/0x7e0 net/ipv4/icmp.c:375
 __icmp_send+0x2ea3/0x30f0 net/ipv4/icmp.c:737
 icmp_send include/net/icmp.h:47 [inline]
 ipv4_link_failure+0x6d/0x230 net/ipv4/route.c:1190
 dst_link_failure include/net/dst.h:427 [inline]
 arp_error_report+0x106/0x1a0 net/ipv4/arp.c:297
 neigh_invalidate+0x359/0x8e0 net/core/neighbour.c:992
 neigh_timer_handler+0xdf2/0x1280 net/core/neighbour.c:1078
 call_timer_fn+0x285/0x600 kernel/time/timer.c:1325
 expire_timers kernel/time/timer.c:1362 [inline]
 __run_timers+0xdb4/0x11d0 kernel/time/timer.c:1681
 run_timer_softirq+0x2e/0x50 kernel/time/timer.c:1694
 __do_softirq+0x53f/0x93a kernel/softirq.c:293

Fixes: 26fc181e6cac ("fou, fou6: do not assume linear skbs")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Stefano Brivio <sbrivio@redhat.com>
Cc: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>