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Date:   Fri, 20 Dec 2019 01:37:09 -0800
From:   syzbot <syzbot+caa188bdfc1eeafeb418@...kaller.appspotmail.com>
To:     davem@...emloft.net, hdanton@...a.com, linux-hams@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        ralf@...ux-mips.org, syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Write in nr_release

syzbot has found a reproducer for the following crash on:

HEAD commit:    7e0165b2 Merge branch 'akpm' (patches from Andrew)
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13d65fa6e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1b59a3066828ac4c
dashboard link: https://syzkaller.appspot.com/bug?extid=caa188bdfc1eeafeb418
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12d9dd51e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+caa188bdfc1eeafeb418@...kaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in atomic_fetch_add  
include/asm-generic/atomic-instrumented.h:111 [inline]
BUG: KASAN: use-after-free in refcount_add include/linux/refcount.h:188  
[inline]
BUG: KASAN: use-after-free in refcount_inc include/linux/refcount.h:228  
[inline]
BUG: KASAN: use-after-free in sock_hold include/net/sock.h:648 [inline]
BUG: KASAN: use-after-free in nr_release+0x65/0x4c0  
net/netrom/af_netrom.c:498
Write of size 4 at addr ffff8880781a3080 by task syz-executor.0/12044

CPU: 1 PID: 12044 Comm: syz-executor.0 Not tainted 5.5.0-rc2-syzkaller #0
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+0x197/0x210 lib/dump_stack.c:118
  print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
  __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
  kasan_report+0x12/0x20 mm/kasan/common.c:639
  check_memory_region_inline mm/kasan/generic.c:185 [inline]
  check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
  __kasan_check_write+0x14/0x20 mm/kasan/common.c:101
  atomic_fetch_add include/asm-generic/atomic-instrumented.h:111 [inline]
  refcount_add include/linux/refcount.h:188 [inline]
  refcount_inc include/linux/refcount.h:228 [inline]
  sock_hold include/net/sock.h:648 [inline]
  nr_release+0x65/0x4c0 net/netrom/af_netrom.c:498
  __sock_release+0xce/0x280 net/socket.c:592
  sock_close+0x1e/0x30 net/socket.c:1270
  __fput+0x2ff/0x890 fs/file_table.c:280
  ____fput+0x16/0x20 fs/file_table.c:313
  task_work_run+0x145/0x1c0 kernel/task_work.c:113
  tracehook_notify_resume include/linux/tracehook.h:188 [inline]
  exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:164
  prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
  do_syscall_64+0x676/0x790 arch/x86/entry/common.c:304
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4144b1
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 1b 00 00 c3 48  
83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48  
89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffc1b260070 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000006 RCX: 00000000004144b1
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 0000000000000001 R08: ffffffffffffffff R09: ffffffffffffffff
R10: 00007ffc1b260150 R11: 0000000000000293 R12: 000000000075c9a0
R13: 000000000075c9a0 R14: 0000000000761390 R15: 000000000075c124

Allocated by task 12049:
  save_stack+0x23/0x90 mm/kasan/common.c:72
  set_track mm/kasan/common.c:80 [inline]
  __kasan_kmalloc mm/kasan/common.c:513 [inline]
  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
  __do_kmalloc mm/slab.c:3656 [inline]
  __kmalloc+0x163/0x770 mm/slab.c:3665
  kmalloc include/linux/slab.h:561 [inline]
  sk_prot_alloc+0x23a/0x310 net/core/sock.c:1603
  sk_alloc+0x39/0xfd0 net/core/sock.c:1657
  nr_create+0xb9/0x5e0 net/netrom/af_netrom.c:411
  __sock_create+0x3ce/0x730 net/socket.c:1420
  sock_create net/socket.c:1471 [inline]
  __sys_socket+0x103/0x220 net/socket.c:1513
  __do_sys_socket net/socket.c:1522 [inline]
  __se_sys_socket net/socket.c:1520 [inline]
  __x64_sys_socket+0x73/0xb0 net/socket.c:1520
  do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 12044:
  save_stack+0x23/0x90 mm/kasan/common.c:72
  set_track mm/kasan/common.c:80 [inline]
  kasan_set_free_info mm/kasan/common.c:335 [inline]
  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
  kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
  __cache_free mm/slab.c:3426 [inline]
  kfree+0x10a/0x2c0 mm/slab.c:3757
  sk_prot_free net/core/sock.c:1640 [inline]
  __sk_destruct+0x5d8/0x7f0 net/core/sock.c:1724
  sk_destruct+0xd5/0x110 net/core/sock.c:1739
  __sk_free+0xfb/0x360 net/core/sock.c:1750
  sk_free+0x83/0xb0 net/core/sock.c:1761
  sock_put include/net/sock.h:1729 [inline]
  nr_release+0x3f4/0x4c0 net/netrom/af_netrom.c:532
  __sock_release+0xce/0x280 net/socket.c:592
  sock_close+0x1e/0x30 net/socket.c:1270
  __fput+0x2ff/0x890 fs/file_table.c:280
  ____fput+0x16/0x20 fs/file_table.c:313
  task_work_run+0x145/0x1c0 kernel/task_work.c:113
  tracehook_notify_resume include/linux/tracehook.h:188 [inline]
  exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:164
  prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
  do_syscall_64+0x676/0x790 arch/x86/entry/common.c:304
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880781a3000
  which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 128 bytes inside of
  2048-byte region [ffff8880781a3000, ffff8880781a3800)
The buggy address belongs to the page:
page:ffffea0001e068c0 refcount:1 mapcount:0 mapping:ffff8880aa400e00  
index:0x0
raw: 00fffe0000000200 ffffea0001e06848 ffffea0001af0088 ffff8880aa400e00
raw: 0000000000000000 ffff8880781a3000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8880781a2f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
  ffff8880781a3000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8880781a3080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                    ^
  ffff8880781a3100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880781a3180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

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