KASAN: slab-out-of-bounds Read in bpf_skb_change_proto

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    a16afaf7928b Merge tag 'for-v4.18' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1338f6bf800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=314f2150f36c16ca
dashboard link: https://syzkaller.appspot.com/bug?extid=d2d729bdde65dee3eae6
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1173381f800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=171f90cf800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+d2d729bdde65dee3eae6@xxxxxxxxxxxxxxxxxxxxxxxxx

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KASAN: slab-out-of-bounds in bpf_skb_proto_xlat net/core/filter.c:2637  
[inline]
BUG: KASAN: slab-out-of-bounds in ____bpf_skb_change_proto  
net/core/filter.c:2675 [inline]
BUG: KASAN: slab-out-of-bounds in bpf_skb_change_proto+0xe37/0x1300  
net/core/filter.c:2650
Read of size 2 at addr ffff8801b04646c0 by task syz-executor241/4519

CPU: 0 PID: 4519 Comm: syz-executor241 Not tainted 4.17.0+ #93
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_load2_noabort+0x14/0x20 mm/kasan/report.c:431
 bpf_skb_proto_xlat net/core/filter.c:2637 [inline]
 ____bpf_skb_change_proto net/core/filter.c:2675 [inline]
 bpf_skb_change_proto+0xe37/0x1300 net/core/filter.c:2650

Allocated by task 0:
(stack is not available)

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8801b04646c0
 which belongs to the cache skbuff_head_cache of size 232
The buggy address is located 0 bytes inside of
 232-byte region [ffff8801b04646c0, ffff8801b04647a8)
The buggy address belongs to the page:
page:ffffea0006c11900 count:1 mapcount:0 mapping:ffff8801d9a0d080 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0006c49388 ffffea0006ae5c48 ffff8801d9a0d080
raw: 0000000000000000 ffff8801b0464080 000000010000000c 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801b0464580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801b0464600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801b0464680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                           ^
 ffff8801b0464700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801b0464780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with  
syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches