bisecting fixing commit since 3ffe1e79c174b2093f7ee3df589a7705572c9620
building syzkaller on acb51638141ff960f547431757130749bc176bc0
testing commit 3ffe1e79c174b2093f7ee3df589a7705572c9620 with gcc (GCC) 8.1.0
kernel signature: 1f3700b8124dee3b6496bd5741ce1396bd3f20aa
run #0: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
run #1: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
run #2: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
run #3: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
run #4: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
run #5: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
run #6: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
run #7: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
run #8: crashed: KASAN: use-after-free Read in bpf_skb_change_tail
run #9: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
testing current HEAD fbc5fe7a54d02e11972e3b2a5ddb6ffc88162c8f
testing commit fbc5fe7a54d02e11972e3b2a5ddb6ffc88162c8f with gcc (GCC) 8.1.0
kernel signature: cd13475d1d831b79ac66356e8df9c69a75e51b12
all runs: crashed: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
revisions tested: 2, total time: 23m59.930547518s (build: 16m21.786019921s, test: 6m39.145640717s)
the crash still happens on HEAD
commit msg: Linux 4.14.157
crash: KASAN: slab-out-of-bounds Read in bpf_skb_change_tail
IPv6: ADDRCONF(NETDEV_UP): hsr0: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): hsr0: link becomes ready
==================================================================
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_hsr: link becomes ready
BUG: KASAN: slab-out-of-bounds in ____bpf_skb_change_tail net/core/filter.c:2371 [inline]
BUG: KASAN: slab-out-of-bounds in bpf_skb_change_tail+0xa77/0xd50 net/core/filter.c:2368
IPv6: ADDRCONF(NETDEV_CHANGE): hsr_slave_1: link becomes ready
Read of size 8 at addr ffff888094d6e490 by task syz-executor.2/6820

CPU: 1 PID: 6820 Comm: syz-executor.2 Not tainted 4.14.157-syzkaller #0
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+0xf7/0x13b lib/dump_stack.c:58
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
 print_address_description.cold.7+0x9/0x1c9 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report.cold.8+0x11a/0x2d3 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 ____bpf_skb_change_tail net/core/filter.c:2371 [inline]
 bpf_skb_change_tail+0xa77/0xd50 net/core/filter.c:2368
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
 bpf_prog_6b83fbf63565f5a7+0x531/0x1000
IPv6: ADDRCONF(NETDEV_UP): veth0_to_bridge: link is not ready
IPv6: ADDRCONF(NETDEV_UP): hsr0: link is not ready
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
Modules linked in:

Allocated by task 0:
CPU: 0 PID: 6818 Comm: syz-executor.1 Not tainted 4.14.157-syzkaller #0
(stack is not available)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

task: ffff8880963c0080 task.stack: ffff88807d4e0000
Freed by task 0:
(stack is not available)
RIP: 0010:__bpf_skb_max_len net/core/filter.c:2284 [inline]
RIP: 0010:____bpf_skb_change_tail net/core/filter.c:2371 [inline]
RIP: 0010:bpf_skb_change_tail+0x53/0xd50 net/core/filter.c:2368

RSP: 0018:ffff88807d4e7928 EFLAGS: 00010206
The buggy address belongs to the object at ffff888094d6e400
 which belongs to the cache skbuff_head_cache of size 232
The buggy address is located 144 bytes inside of
 232-byte region [ffff888094d6e400, ffff888094d6e4e8)
The buggy address belongs to the page:
RAX: dffffc0000000000 RBX: ffff8880a95dc340 RCX: 0000000000000048
RDX: 0000000000000000 RSI: 0000000000000008 RDI: 0000000000000241
page:ffffea0002535b80 count:1 mapcount:0 mapping:ffff888094d6e040 index:0x0
RBP: ffff88807d4e7980 R08: ffff8880963c0920 R09: 0000000000000000
R10: 0000000000000000 R11: ffff8880963c0080 R12: 0000000000000019
flags: 0x1fffc0000000100(slab)
R13: 0000000000000018 R14: ffffc90005ed4000 R15: ffff8880a95dc540
raw: 01fffc0000000100 ffff888094d6e040 0000000000000000 000000010000000c
FS:  00007f80dabec700(0000) GS:ffff8880aee00000(0000) knlGS:0000000000000000
raw: ffffea0001f52a60 ffffea000257a1a0 ffff8880a9e19a80 0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
page dumped because: kasan: bad access detected
CR2: 000000000075c091 CR3: 0000000097591000 CR4: 00000000001406f0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Memory state around the buggy address:
 ffff888094d6e380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 ffff888094d6e400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
Call Trace:
>ffff888094d6e480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                         ^
 ffff888094d6e500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 bpf_prog_6b83fbf63565f5a7+0x5e6/0x1000
 ffff888094d6e580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================