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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 ffff8801be7a1b0b by task syz-executor6/12944

CPU: 1 PID: 12944 Comm: syz-executor6 Not tainted 4.15.0-rc9+ #279
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: 0033:0x452f19
RSP: 002b:00007f9008555c58 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452f19
RDX: 000000000000002b RSI: 0000000020012fd5 RDI: 0000000000000015
RBP: 00000000000003d6 R08: 0000000020008000 R09: 000000000000001c
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4cb0
R13: 00000000ffffffff R14: 00007f90085566d4 R15: 0000000000000000

Allocated by task 3706:
 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
 __do_kmalloc_node mm/slab.c:3672 [inline]
 __kmalloc_node+0x47/0x70 mm/slab.c:3679
 kmalloc_node include/linux/slab.h:541 [inline]
 kvmalloc_node+0x99/0xd0 mm/util.c:397
 kvmalloc include/linux/mm.h:541 [inline]
 kvmalloc_array include/linux/mm.h:557 [inline]
 alloc_fdtable+0xcf/0x280 fs/file.c:120
 dup_fd+0x8b8/0xdf0 fs/file.c:315
 copy_files kernel/fork.c:1300 [inline]
 copy_process.part.38+0x1fe6/0x4b20 kernel/fork.c:1740
 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 9382:
 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]
 kfree+0xd6/0x260 mm/slab.c:3803
 kvfree+0x36/0x60 mm/util.c:416
 __free_fdtable+0x31/0x70 fs/file.c:36
 put_files_struct+0x28e/0x330 fs/file.c:425
 exit_files+0x83/0xb0 fs/file.c:450
 do_exit+0x994/0x1ad0 kernel/exit.c:860
 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 ffff8801be7a1600
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1291 bytes inside of
 2048-byte region [ffff8801be7a1600, ffff8801be7a1e00)
The buggy address belongs to the page:
page:ffffea0006f9e800 count:1 mapcount:0 mapping:ffff8801be7a0500 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801be7a0500 0000000000000000 0000000100000003
raw: ffffea0006f9b4a0 ffffea0006f733a0 ffff8801dac00c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801be7a1a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801be7a1a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801be7a1b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff8801be7a1b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801be7a1c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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