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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 ffff8801c065780b by task syzkaller892192/3663

CPU: 0 PID: 3663 Comm: syzkaller892192 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: 0033:0x446699
RSP: 002b:00007fff5c7b4b18 EFLAGS: 00000216 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000000068 RCX: 0000000000446699
RDX: 0000000000000000 RSI: 0000000020003fd9 RDI: 0000000000000004
RBP: 00000000004a80c6 R08: 0000000020008000 R09: 000000000000001c
R10: 0000000000000001 R11: 0000000000000216 R12: 00000000004037d0
R13: 0000000000403860 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 3415:
 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:2590
 user_path_at include/linux/namei.h:57 [inline]
 vfs_statx+0xe9/0x190 fs/stat.c:185
 vfs_stat include/linux/fs.h:3080 [inline]
 SYSC_newstat+0x87/0xf0 fs/stat.c:337
 SyS_newstat+0x1d/0x30 fs/stat.c:333
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 3415:
 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:2345
 user_path_at_empty+0x40/0x50 fs/namei.c:2590
 user_path_at include/linux/namei.h:57 [inline]
 vfs_statx+0xe9/0x190 fs/stat.c:185
 vfs_stat include/linux/fs.h:3080 [inline]
 SYSC_newstat+0x87/0xf0 fs/stat.c:337
 SyS_newstat+0x1d/0x30 fs/stat.c:333
 entry_SYSCALL_64_fastpath+0x29/0xa0

The buggy address belongs to the object at ffff8801c0656b80
 which belongs to the cache names_cache of size 4096
The buggy address is located 3211 bytes inside of
 4096-byte region [ffff8801c0656b80, ffff8801c0657b80)
The buggy address belongs to the page:
page:ffffea0007019580 count:1 mapcount:0 mapping:ffff8801c0656b80 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801c0656b80 0000000000000000 0000000100000001
raw: ffffea00070196a0 ffffea00070194a0 ffff8801dae2c600 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c0657700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c0657780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801c0657800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff8801c0657880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c0657900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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