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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 ffff8801bcf675cb by task syz-executor5/20891

CPU: 1 PID: 20891 Comm: syz-executor5 Not tainted 4.15.0+ #198
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
 do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
 do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
 entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:129
RIP: 0023:0xf7f07c79
RSP: 002b:00000000f770308c EFLAGS: 00000296 ORIG_RAX: 0000000000000171
RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 0000000020003fd9
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000020008000
RBP: 000000000000001c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 19237:
 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
 getname_flags+0xcb/0x580 fs/namei.c:138
 user_path_at_empty+0x2d/0x50 fs/namei.c:2587
 user_path_at include/linux/namei.h:57 [inline]
 SYSC_faccessat fs/open.c:384 [inline]
 SyS_faccessat fs/open.c:353 [inline]
 SYSC_access fs/open.c:431 [inline]
 SyS_access+0x22c/0x6a0 fs/open.c:429
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 19237:
 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
 putname+0xee/0x130 fs/namei.c:258
 filename_lookup+0x315/0x500 fs/namei.c:2342
 user_path_at_empty+0x40/0x50 fs/namei.c:2587
 user_path_at include/linux/namei.h:57 [inline]
 SYSC_faccessat fs/open.c:384 [inline]
 SyS_faccessat fs/open.c:353 [inline]
 SYSC_access fs/open.c:431 [inline]
 SyS_access+0x22c/0x6a0 fs/open.c:429
 entry_SYSCALL_64_fastpath+0x29/0xa0

The buggy address belongs to the object at ffff8801bcf66e80
 which belongs to the cache names_cache of size 4096
The buggy address is located 1867 bytes inside of
 4096-byte region [ffff8801bcf66e80, ffff8801bcf67e80)
The buggy address belongs to the page:
page:ffffea0006f3d980 count:1 mapcount:0 mapping:ffff8801bcf66e80 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801bcf66e80 0000000000000000 0000000100000001
raw: ffffea0006f3d920 ffffea0006a43b20 ffff8801da9d2600 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801bcf67480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bcf67500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801bcf67580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff8801bcf67600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bcf67680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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