KASAN: wild-memory-access Read in fib6_purge_rt

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: dce5cccc nfp: ensure skb network header is set for packet ..
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=1465f91ea00000
kernel config: https://syzkaller.appspot.com/x/.config?x=e8b7a9cd7feeb720
dashboard link: https://syzkaller.appspot.com/bug?extid=d490ec8b6b62bf9f5be6
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+d490ec...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: wild-memory-access in atomic_read
include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: wild-memory-access in refcount_sub_and_test_checked+0x87/0x200
lib/refcount.c:182
Read of size 4 at addr 0000ffff88808b18 by task syz-executor.0/25937

CPU: 0 PID: 25937 Comm: syz-executor.0 Not tainted 5.2.0-rc3+ #47
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_sub_and_test_checked+0x87/0x200 lib/refcount.c:182
refcount_dec_and_test_checked+0x1b/0x20 lib/refcount.c:220
fib6_info_release include/net/ip6_fib.h:294 [inline]
fib6_info_release include/net/ip6_fib.h:292 [inline]
fib6_drop_pcpu_from net/ipv6/ip6_fib.c:922 [inline]
fib6_purge_rt+0x1d2/0x5e0 net/ipv6/ip6_fib.c:933
fib6_del_route net/ipv6/ip6_fib.c:1808 [inline]
fib6_del+0xac2/0x10a0 net/ipv6/ip6_fib.c:1839
fib6_clean_node+0x3a5/0x590 net/ipv6/ip6_fib.c:2001
fib6_walk_continue+0x4a9/0x8e0 net/ipv6/ip6_fib.c:1923
fib6_walk+0x9d/0x100 net/ipv6/ip6_fib.c:1971
fib6_clean_tree+0xe0/0x120 net/ipv6/ip6_fib.c:2050
__fib6_clean_all+0x118/0x2a0 net/ipv6/ip6_fib.c:2066
fib6_clean_all+0x2b/0x40 net/ipv6/ip6_fib.c:2077
rt6_sync_down_dev+0x134/0x150 net/ipv6/route.c:4165
rt6_disable_ip+0x27/0x5f0 net/ipv6/route.c:4170
addrconf_ifdown+0xa2/0x1220 net/ipv6/addrconf.c:3705
addrconf_notify+0x5db/0x2270 net/ipv6/addrconf.c:3630
notifier_call_chain+0xc2/0x230 kernel/notifier.c:95
__raw_notifier_call_chain kernel/notifier.c:396 [inline]
raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:403
call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1749
call_netdevice_notifiers_extack net/core/dev.c:1761 [inline]
call_netdevice_notifiers net/core/dev.c:1775 [inline]
__dev_notify_flags+0x1e9/0x2c0 net/core/dev.c:7590
dev_change_flags+0x10d/0x170 net/core/dev.c:7626
devinet_ioctl+0x138a/0x1c50 net/ipv4/devinet.c:1100
inet_ioctl+0x1f4/0x340 net/ipv4/af_inet.c:948
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:00007f59a74b1c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459279
RDX: 0000000020000040 RSI: 0000000000008914 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f59a74b26d4
R13: 00000000004c4eaf R14: 00000000004d8ee0 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.