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BUG: KASAN: use-after-free in decode_session6+0xe7c/0x1580 net/xfrm/xfrm_policy.c:3393
Read of size 1 at addr ffff888042dd00af by task syz-executor.3/25190

CPU: 0 PID: 25190 Comm: syz-executor.3 Not tainted 5.10.0-rc2-next-20201104-syzkaller #0
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+0x107/0x163 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x4c8 mm/kasan/report.c:385
 __kasan_report mm/kasan/report.c:545 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562
 decode_session6+0xe7c/0x1580 net/xfrm/xfrm_policy.c:3393
 __xfrm_decode_session net/xfrm/xfrm_policy.c:3485 [inline]
 __xfrm_policy_check+0x2fa/0x2850 net/xfrm/xfrm_policy.c:3540
 __xfrm_policy_check2 include/net/xfrm.h:1097 [inline]
 xfrm_policy_check include/net/xfrm.h:1106 [inline]
 sctp_rcv+0x12b0/0x2e30 net/sctp/input.c:202
 sctp6_rcv+0x22/0x40 net/sctp/ipv6.c:1078
 ip6_protocol_deliver_rcu+0x2e8/0x1680 net/ipv6/ip6_input.c:433
 ip6_input_finish+0x7f/0x160 net/ipv6/ip6_input.c:474
 NF_HOOK include/linux/netfilter.h:301 [inline]
 NF_HOOK include/linux/netfilter.h:295 [inline]
 ip6_input+0x9c/0xd0 net/ipv6/ip6_input.c:483
 dst_input include/net/dst.h:447 [inline]
 ip6_rcv_finish net/ipv6/ip6_input.c:76 [inline]
 NF_HOOK include/linux/netfilter.h:301 [inline]
 NF_HOOK include/linux/netfilter.h:295 [inline]
 ipv6_rcv+0x28e/0x3c0 net/ipv6/ip6_input.c:307
 __netif_receive_skb_one_core+0x114/0x180 net/core/dev.c:5315
 __netif_receive_skb+0x27/0x1c0 net/core/dev.c:5429
 process_backlog+0x232/0x6c0 net/core/dev.c:6319
 napi_poll net/core/dev.c:6763 [inline]
 net_rx_action+0x4dc/0x1100 net/core/dev.c:6833
 __do_softirq+0x2a0/0x9f6 kernel/softirq.c:298
 asm_call_irq_on_stack+0xf/0x20
 </IRQ>
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline]
 do_softirq_own_stack+0xaa/0xd0 arch/x86/kernel/irq_64.c:77
 do_softirq kernel/softirq.c:343 [inline]
 do_softirq+0xb5/0xe0 kernel/softirq.c:330
 __local_bh_enable_ip+0xf0/0x110 kernel/softirq.c:195
 local_bh_enable include/linux/bottom_half.h:32 [inline]
 rcu_read_unlock_bh include/linux/rcupdate.h:731 [inline]
 ip6_finish_output2+0x71f/0x16c0 net/ipv6/ip6_output.c:118
 __ip6_finish_output net/ipv6/ip6_output.c:143 [inline]
 __ip6_finish_output+0x447/0xab0 net/ipv6/ip6_output.c:128
 ip6_finish_output+0x34/0x1f0 net/ipv6/ip6_output.c:153
 NF_HOOK_COND include/linux/netfilter.h:290 [inline]
 ip6_output+0x1db/0x520 net/ipv6/ip6_output.c:176
 dst_output include/net/dst.h:441 [inline]
 NF_HOOK include/linux/netfilter.h:301 [inline]
 NF_HOOK include/linux/netfilter.h:295 [inline]
 ip6_xmit+0x1258/0x1e80 net/ipv6/ip6_output.c:280
 sctp_v6_xmit+0xbf3/0xfe0 net/sctp/ipv6.c:223
 sctp_packet_transmit+0x1f44/0x32f0 net/sctp/output.c:627
 sctp_packet_transmit_chunk+0x117/0x260 net/sctp/output.c:192
 sctp_outq_flush_data net/sctp/outqueue.c:1092 [inline]
 sctp_outq_flush+0xdd1/0x2580 net/sctp/outqueue.c:1191
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1801 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1185 [inline]
 sctp_do_sm+0x74e/0x5120 net/sctp/sm_sideeffect.c:1156
 sctp_primitive_SEND+0x9b/0xc0 net/sctp/primitive.c:163
 sctp_sendmsg_to_asoc+0x183c/0x2180 net/sctp/socket.c:1855
 sctp_sendmsg+0x103b/0x1d30 net/sctp/socket.c:2013
 inet_sendmsg+0x99/0xe0 net/ipv4/af_inet.c:817
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:671
 sock_no_sendpage+0xee/0x130 net/core/sock.c:2833
 kernel_sendpage net/socket.c:3657 [inline]
 sock_sendpage+0x113/0x140 net/socket.c:944
 pipe_to_sendpage+0x2ad/0x380 fs/splice.c:364
 splice_from_pipe_feed fs/splice.c:418 [inline]
 __splice_from_pipe+0x439/0x8a0 fs/splice.c:562
 splice_from_pipe fs/splice.c:597 [inline]
 generic_splice_sendpage+0xd4/0x140 fs/splice.c:743
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x110/0x180 fs/splice.c:933
 splice_direct_to_actor+0x38c/0x980 fs/splice.c:888
 do_splice_direct+0x1b3/0x280 fs/splice.c:976
 do_sendfile+0x55f/0xd40 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1318 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1304
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45deb9
Code: 0d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 db b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb6e6d3cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000027f40 RCX: 000000000045deb9
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000004
RBP: 000000000118bf68 R08: 0000000000000000 R09: 0000000000000000
R10: 000080001d00c0d0 R11: 0000000000000246 R12: 000000000118bf2c
R13: 00007fff940c0a5f R14: 00007fb6e6d3d9c0 R15: 000000000118bf2c

The buggy address belongs to the page:
page:00000000b46e8517 refcount:0 mapcount:-128 mapping:0000000000000000 index:0xffff888042dd6000 pfn:0x42dd0
flags: 0xfff00000000000()
raw: 00fff00000000000 ffff88813fffb978 ffffea00019a7408 0000000000000000
raw: ffff888042dd6000 0000000000000003 00000000ffffff7f 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888042dcff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888042dd0000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888042dd0080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                  ^
 ffff888042dd0100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888042dd0180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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