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BUG: KASAN: use-after-free in erspan_build_header+0x3bf/0x3d0 net/ipv4/ip_gre.c:698
Read of size 2 at addr ffff8801c05d608b by task syz-executor2/8496

CPU: 1 PID: 8496 Comm: syz-executor2 Not tainted 4.15.0-rc9+ #274
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load_n_noabort+0xf/0x20 mm/kasan/report.c:440
 erspan_build_header+0x3bf/0x3d0 net/ipv4/ip_gre.c:698
 erspan_xmit+0x3b8/0x13b0 net/ipv4/ip_gre.c:740
 __netdev_start_xmit include/linux/netdevice.h:4042 [inline]
 netdev_start_xmit include/linux/netdevice.h:4051 [inline]
 packet_direct_xmit+0x315/0x6b0 net/packet/af_packet.c:266
 packet_snd net/packet/af_packet.c:2943 [inline]
 packet_sendmsg+0x3aed/0x60b0 net/packet/af_packet.c:2968
 sock_sendmsg_nosec net/socket.c:638 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:648
 SYSC_sendto+0x361/0x5c0 net/socket.c:1729
 SyS_sendto+0x40/0x50 net/socket.c:1697
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x452ef9
RSP: 002b:00007f9f8e39dc58 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 000000000071bf58 RCX: 0000000000452ef9
RDX: 0000000000000000 RSI: 0000000020003fd9 RDI: 0000000000000016
RBP: 000000000000034e R08: 0000000020008000 R09: 000000000000001c
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f3ff0
R13: 00000000ffffffff R14: 00007f9f8e39e6d4 R15: 0000000000000002

Allocated by task 1815:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc_node+0x144/0x760 mm/slab.c:3634
 __alloc_skb+0xf1/0x780 net/core/skbuff.c:193
 alloc_skb include/linux/skbuff.h:983 [inline]
 netlink_alloc_large_skb net/netlink/af_netlink.c:1147 [inline]
 netlink_sendmsg+0xa86/0xe60 net/netlink/af_netlink.c:1839
 sock_sendmsg_nosec net/socket.c:638 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:648
 ___sys_sendmsg+0x767/0x8b0 net/socket.c:2028
 __sys_sendmsg+0xe5/0x210 net/socket.c:2062
 SYSC_sendmsg net/socket.c:2073 [inline]
 SyS_sendmsg+0x2d/0x50 net/socket.c:2069
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 3635:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3488 [inline]
 kmem_cache_free+0x83/0x2a0 mm/slab.c:3746
 kfree_skbmem+0x1a1/0x1d0 net/core/skbuff.c:582
 __kfree_skb net/core/skbuff.c:642 [inline]
 consume_skb+0x15b/0x490 net/core/skbuff.c:701
 skb_free_datagram+0x1a/0xe0 net/core/datagram.c:331
 netlink_recvmsg+0x5cf/0x1300 net/netlink/af_netlink.c:1943
 sock_recvmsg_nosec net/socket.c:811 [inline]
 sock_recvmsg+0xc9/0x110 net/socket.c:818
 ___sys_recvmsg+0x2a4/0x640 net/socket.c:2187
 __sys_recvmsg+0xe2/0x210 net/socket.c:2232
 SYSC_recvmsg net/socket.c:2244 [inline]
 SyS_recvmsg+0x2d/0x50 net/socket.c:2239
 entry_SYSCALL_64_fastpath+0x29/0xa0

The buggy address belongs to the object at ffff8801c05d6040
 which belongs to the cache skbuff_head_cache of size 232
The buggy address is located 75 bytes inside of
 232-byte region [ffff8801c05d6040, ffff8801c05d6128)
The buggy address belongs to the page:
page:ffffea0007017580 count:1 mapcount:0 mapping:ffff8801c05d6040 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c05d6040 0000000000000000 000000010000000c
raw: ffffea00073915a0 ffffea0007008820 ffff8801d986ccc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c05d5f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801c05d6000: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>ffff8801c05d6080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff8801c05d6100: fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc
 ffff8801c05d6180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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