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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 ffff8801b3be530b by task syz-executor4/5949

CPU: 0 PID: 5949 Comm: syz-executor4 Not tainted 4.15.0+ #286
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: 0033:0x453299
RSP: 002b:00007fdccaec5c58 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007fdccaec6700 RCX: 0000000000453299
RDX: 0000000000000000 RSI: 0000000020003fd9 RDI: 0000000000000014
RBP: 0000000000000000 R08: 0000000020008000 R09: 000000000000001c
R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
R13: 0000000000a2f33f R14: 00007fdccaec69c0 R15: 0000000000000000

Allocated by task 4219:
 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+0x12e/0x760 mm/slab.c:3544
 dup_mmap kernel/fork.c:653 [inline]
 dup_mm kernel/fork.c:1196 [inline]
 copy_mm+0x8d7/0x131b kernel/fork.c:1250
 copy_process.part.38+0x1ee9/0x4b20 kernel/fork.c:1752
 copy_process kernel/fork.c:1565 [inline]
 _do_fork+0x1f7/0xfe0 kernel/fork.c:2044
 SYSC_clone kernel/fork.c:2154 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2148
 do_syscall_64+0x273/0x920 arch/x86/entry/common.c:285
 return_from_SYSCALL_64+0x0/0x75

Freed by task 5720:
 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
 remove_vma+0x162/0x1b0 mm/mmap.c:176
 exit_mmap+0x311/0x500 mm/mmap.c:3049
 __mmput kernel/fork.c:923 [inline]
 mmput+0x223/0x6d0 kernel/fork.c:944
 exit_mm kernel/exit.c:544 [inline]
 do_exit+0x90a/0x1ad0 kernel/exit.c:852
 do_group_exit+0x149/0x400 kernel/exit.c:968
 get_signal+0x73f/0x16c0 kernel/signal.c:2335
 do_signal+0x90/0x1eb0 arch/x86/kernel/signal.c:809
 exit_to_usermode_loop+0x214/0x310 arch/x86/entry/common.c:158
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264
 entry_SYSCALL_64_fastpath+0x9e/0xa0

The buggy address belongs to the object at ffff8801b3be5250
 which belongs to the cache vm_area_struct of size 200
The buggy address is located 187 bytes inside of
 200-byte region [ffff8801b3be5250, ffff8801b3be5318)
The buggy address belongs to the page:
page:ffffea0006cef940 count:1 mapcount:0 mapping:ffff8801b3be5040 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801b3be5040 0000000000000000 000000010000000f
raw: ffffea0006cd55e0 ffffea0006cc6760 ffff8801da9c1840 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801b3be5200: fb fb fc fc fc fc fc fc fc fc fb fb fb fb fb fb
 ffff8801b3be5280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801b3be5300: fb fb fb fc fc fc fc fc fc fc fc fb fb fb fb fb
                      ^
 ffff8801b3be5380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801b3be5400: fb fb fb fb fc fc fc fc fc fc fc fc fb fb fb fb
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