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BUG: KASAN: slab-out-of-bounds in erspan_build_header+0x3bf/0x3d0 net/ipv4/ip_gre.c:698
Read of size 2 at addr ffff8801cac0a78b by task syz-executor0/32015

CPU: 0 PID: 32015 Comm: syz-executor0 Not tainted 4.15.0-rc9+ #276
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:00007faaea9b7c58 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007faaea9b8700 RCX: 0000000000452f19
RDX: 0000000000000000 RSI: 0000000020011000 RDI: 0000000000000013
RBP: 0000000000000000 R08: 0000000020008000 R09: 000000000000001c
R10: 0000000004000000 R11: 0000000000000212 R12: 0000000000000000
R13: 0000000000a2f7cf R14: 00007faaea9b89c0 R15: 0000000000000000

Allocated by task 3645:
 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
 kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3610
 kmalloc include/linux/slab.h:499 [inline]
 kzalloc include/linux/slab.h:688 [inline]
 kernfs_iop_get_link+0x6e/0x580 fs/kernfs/symlink.c:124
 generic_readlink fs/namei.c:4679 [inline]
 vfs_readlink+0x1b6/0x4f0 fs/namei.c:4714
 SYSC_readlinkat fs/stat.c:406 [inline]
 SyS_readlinkat fs/stat.c:382 [inline]
 SYSC_readlink fs/stat.c:421 [inline]
 SyS_readlink+0x2ca/0x3a0 fs/stat.c:418
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 3645:
 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
 kfree_link+0x15/0x20 fs/libfs.c:1066
 do_delayed_call include/linux/delayed_call.h:28 [inline]
 generic_readlink fs/namei.c:4684 [inline]
 vfs_readlink+0x23f/0x4f0 fs/namei.c:4714
 SYSC_readlinkat fs/stat.c:406 [inline]
 SyS_readlinkat fs/stat.c:382 [inline]
 SYSC_readlink fs/stat.c:421 [inline]
 SyS_readlink+0x2ca/0x3a0 fs/stat.c:418
 entry_SYSCALL_64_fastpath+0x29/0xa0

The buggy address belongs to the object at ffff8801cac0ae40
 which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 1717 bytes to the left of
 4096-byte region [ffff8801cac0ae40, ffff8801cac0be40)
The buggy address belongs to the page:
page:ffffea00072b0280 count:1 mapcount:0 mapping:ffff8801cac0ae40 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801cac0ae40 0000000000000000 0000000100000001
raw: ffffea00072bc720 ffffea00072ab6a0 ffff8801dac00dc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801cac0a680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801cac0a700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801cac0a780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                      ^
 ffff8801cac0a800: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801cac0a880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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