KASAN: use-after-free Read in nr_rx_frame

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: e1ef035d272e Merge tag 'armsoc-defconfig' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=166315fd400000
kernel config: https://syzkaller.appspot.com/x/.config?x=9c6a26e22579190b
dashboard link: https://syzkaller.appspot.com/bug?extid=72f911fa716e011378ae
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=172848bb400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+72f911...@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
8021q: adding VLAN 0 to HW filter on device batadv0
8021q: adding VLAN 0 to HW filter on device batadv0
==================================================================
BUG: KASAN: use-after-free in sk_acceptq_added include/net/sock.h:855
[inline]
BUG: KASAN: use-after-free in nr_rx_frame+0x1c5f/0x1d50
net/netrom/af_netrom.c:1012
Read of size 4 at addr ffff8880969d07e8 by task swapper/0/0

CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.20.0+ #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1db/0x2d0 lib/dump_stack.c:113
print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
__asan_report_load4_noabort+0x14/0x20 mm/kasan/generic_report.c:134
sk_acceptq_added include/net/sock.h:855 [inline]
nr_rx_frame+0x1c5f/0x1d50 net/netrom/af_netrom.c:1012
nr_loopback_timer+0x7b/0x170 net/netrom/nr_loopback.c:62
call_timer_fn+0x254/0x900 kernel/time/timer.c:1325
expire_timers kernel/time/timer.c:1362 [inline]
__run_timers+0x6fc/0xd50 kernel/time/timer.c:1681
run_timer_softirq+0x52/0xb0 kernel/time/timer.c:1694
__do_softirq+0x30b/0xb11 kernel/softirq.c:292
invoke_softirq kernel/softirq.c:373 [inline]
irq_exit+0x180/0x1d0 kernel/softirq.c:413
exiting_irq arch/x86/include/asm/apic.h:536 [inline]
smp_apic_timer_interrupt+0x1b7/0x760 arch/x86/kernel/apic/apic.c:1062
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807
</IRQ>
RIP: 0010:native_safe_halt+0x2/0x10 arch/x86/include/asm/irqflags.h:58
Code: ff ff ff 48 89 c7 48 89 45 d8 e8 59 49 d3 f9 48 8b 45 d8 e9 ce fe ff
ff 48 89 df e8 48 49 d3 f9 eb 82 90 90 90 90 90 90 fb f4 <c3> 0f 1f 00 66
2e 0f 1f 84 00 00 00 00 00 f4 c3 90 90 90 90 90 90
RSP: 0018:ffffffff89807c60 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff13249e9 RBX: 1ffffffff1300f8f RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffffffff8987b73c
RBP: ffffffff89807d20 R08: ffffffff8987aec0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffffff89807cf8 R14: 0000000000000000 R15: ffffffff89924f38
arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:555
default_idle_call+0x36/0x90 kernel/sched/idle.c:93
cpuidle_idle_call kernel/sched/idle.c:153 [inline]
do_idle+0x386/0x5d0 kernel/sched/idle.c:262
cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:353
rest_init+0x245/0x37b init/main.c:443
arch_call_rest_init+0xe/0x1b
start_kernel+0x882/0x8bd init/main.c:741
x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:470
x86_64_start_kernel+0x77/0x7b arch/x86/kernel/head64.c:451
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

Allocated by task 10788:
save_stack+0x45/0xd0 mm/kasan/common.c:73
set_track mm/kasan/common.c:85 [inline]
kasan_kmalloc mm/kasan/common.c:482 [inline]
kasan_kmalloc+0xcf/0xe0 mm/kasan/common.c:455
__do_kmalloc mm/slab.c:3709 [inline]
__kmalloc+0x15c/0x740 mm/slab.c:3718
kmalloc include/linux/slab.h:550 [inline]
sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1477
sk_alloc+0xd7/0x1690 net/core/sock.c:1531
nr_create+0xb9/0x5e0 net/netrom/af_netrom.c:436
__sock_create+0x532/0x930 net/socket.c:1277
sock_create net/socket.c:1317 [inline]
__sys_socket+0x106/0x260 net/socket.c:1347
__do_sys_socket net/socket.c:1356 [inline]
__se_sys_socket net/socket.c:1354 [inline]
__x64_sys_socket+0x73/0xb0 net/socket.c:1354
do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 10834:
save_stack+0x45/0xd0 mm/kasan/common.c:73
set_track mm/kasan/common.c:85 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:444
kasan_slab_free+0xe/0x10 mm/kasan/common.c:452
__cache_free mm/slab.c:3485 [inline]
kfree+0xcf/0x230 mm/slab.c:3804
sk_prot_free net/core/sock.c:1514 [inline]
__sk_destruct+0x76d/0xa60 net/core/sock.c:1596
sk_destruct+0x7b/0x90 net/core/sock.c:1604
__sk_free+0xce/0x300 net/core/sock.c:1615
sk_free+0x42/0x50 net/core/sock.c:1626
sock_put include/net/sock.h:1703 [inline]
nr_release+0x337/0x3c0 net/netrom/af_netrom.c:557
__sock_release+0xd3/0x250 net/socket.c:579
sock_close+0x1b/0x30 net/socket.c:1141
__fput+0x3c5/0xb10 fs/file_table.c:278
____fput+0x16/0x20 fs/file_table.c:309
task_work_run+0x1f4/0x2b0 kernel/task_work.c:113
get_signal+0x168d/0x19b0 kernel/signal.c:2347
do_signal+0x91/0x1e80 arch/x86/kernel/signal.c:816
exit_to_usermode_loop+0x2f7/0x3b0 arch/x86/entry/common.c:162
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x696/0x800 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880969d0440
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 936 bytes inside of
2048-byte region [ffff8880969d0440, ffff8880969d0c40)
The buggy address belongs to the page:
page:ffffea00025a7400 count:1 mapcount:0 mapping:ffff88812c3f0c40 index:0x0
compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea000292f708 ffffea00023ae408 ffff88812c3f0c40
raw: 0000000000000000 ffff8880969d0440 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880969d0680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880969d0700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8880969d0780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880969d0800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880969d0880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger
crash:

Reported-and-tested-by:
syzbot+72f911...@syzkaller.appspotmail.com

Tested on:

commit: d63967e475ae isdn: fix kernel-infoleak in capi_unlocked_io..
git tree: net
kernel config: https://syzkaller.appspot.com/x/.config?x=b6c41ffa3d657353

compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Note: testing is done by a robot and is best-effort only.

[Cong Wang]

#syz fix: netrom: fix locking in nr_find_socket()