==================================================================
BUG: KASAN: use-after-free in pskb_may_pull include/linux/skbuff.h:2106 [inline]
BUG: KASAN: use-after-free in skb_ensure_writable+0x554/0x620 net/core/skbuff.c:5118
Read of size 4 at addr ffff8801bcefafc0 by task syz-executor2/18114

CPU: 1 PID: 18114 Comm: syz-executor2 Not tainted 4.17.0-rc7+ #38
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 print_address_description+0x6c/0x20b mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
 pskb_may_pull include/linux/skbuff.h:2106 [inline]
 skb_ensure_writable+0x554/0x620 net/core/skbuff.c:5118
 __bpf_try_make_writable net/core/filter.c:1606 [inline]
 bpf_try_make_writable net/core/filter.c:1612 [inline]
 ____bpf_l4_csum_replace net/core/filter.c:1822 [inline]
 bpf_l4_csum_replace+0x91/0x4a0 net/core/filter.c:1809

The buggy address belongs to the page:
page:ffffea0006f3be80 count:0 mapcount:-127 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffff80
raw: ffffea00066a97e0 ffffea0006af0ba0 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801bcefae80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801bcefaf00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8801bcefaf80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                           ^
 ffff8801bcefb000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bcefb080: fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc
==================================================================