KASAN: null-ptr-deref Read in ipv4_neigh_lookup

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 38e406f6 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=1275df5aa00000
kernel config: https://syzkaller.appspot.com/x/.config?x=60564cb52ab29d5b
dashboard link: https://syzkaller.appspot.com/bug?extid=2f6c5985516d90580e1b
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [da...@davemloft.net kuz...@ms2.inr.ac.ru
linux-...@vger.kernel.org net...@vger.kernel.org yosh...@linux-ipv6.org
net...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2f6c59...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in atomic_read
include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: null-ptr-deref in refcount_inc_not_zero_checked+0x81/0x200
lib/refcount.c:123
Read of size 4 at addr 000000000000004a by task syz-executor.5/18798

CPU: 0 PID: 18798 Comm: syz-executor.5 Not tainted 5.2.0-rc3+ #45
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+0x172/0x1f0 lib/dump_stack.c:113
__kasan_report.cold+0x5/0x40 mm/kasan/report.c:321
kasan_report+0x12/0x20 mm/kasan/common.c:614
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x123/0x190 mm/kasan/generic.c:191
kasan_check_read+0x11/0x20 mm/kasan/common.c:94
atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
refcount_inc_not_zero_checked+0x81/0x200 lib/refcount.c:123
ipv4_neigh_lookup+0x44e/0x1590 net/ipv4/route.c:450
dst_neigh_lookup_skb include/net/dst.h:401 [inline]
__neigh_update+0xba7/0x2570 net/core/neighbour.c:1379
neigh_update+0x37/0x50 net/core/neighbour.c:1412
arp_req_set+0x2e7/0x720 net/ipv4/arp.c:1068
arp_ioctl+0x652/0x7f0 net/ipv4/arp.c:1226
inet_ioctl+0x2a0/0x340 net/ipv4/af_inet.c:926
sock_do_ioctl+0xd8/0x2f0 net/socket.c:1043
sock_ioctl+0x3ed/0x780 net/socket.c:1194
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459279
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ff9f28f6c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459279
RDX: 0000000020000240 RSI: 0000000000008955 RDI: 0000000000000006
RBP: 000000000075bfc0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ff9f28f76d4
R13: 00000000004c4e7a R14: 00000000004d8e80 R15: 00000000ffffffff
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.