KASAN: null-ptr-deref Write in rxrpc_unuse_local

KASAN: null-ptr-deref Write in rxrpc_unuse_local

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    87b983f5 Add linux-next specific files for 20190809
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=143aecee600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=28eea330e11df0eb
dashboard link: https://syzkaller.appspot.com/bug?extid=20dee719a2e090427b5f
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17ceae36600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10ebc40e600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+20dee719a2e090427b5f@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in atomic_sub_return  
include/asm-generic/atomic-instrumented.h:159 [inline]
BUG: KASAN: null-ptr-deref in atomic_dec_return  
include/linux/atomic-fallback.h:455 [inline]
BUG: KASAN: null-ptr-deref in rxrpc_unuse_local+0x23/0x70  
net/rxrpc/local_object.c:405
Write of size 4 at addr 0000000000000010 by task syz-executor725/10010

CPU: 1 PID: 10010 Comm: syz-executor725 Not tainted 5.3.0-rc3-next-20190809  
#63
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+0x5/0x36 mm/kasan/report.c:486
  kasan_report+0x12/0x17 mm/kasan/common.c:610
  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:98
  atomic_sub_return include/asm-generic/atomic-instrumented.h:159 [inline]
  atomic_dec_return include/linux/atomic-fallback.h:455 [inline]
  rxrpc_unuse_local+0x23/0x70 net/rxrpc/local_object.c:405
  rxrpc_release_sock net/rxrpc/af_rxrpc.c:904 [inline]
  rxrpc_release+0x47d/0x840 net/rxrpc/af_rxrpc.c:930
  __sock_release+0xce/0x280 net/socket.c:590
  sock_close+0x1e/0x30 net/socket.c:1268
  __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
  exit_task_work include/linux/task_work.h:22 [inline]
  do_exit+0x92f/0x2e50 kernel/exit.c:879
  do_group_exit+0x135/0x360 kernel/exit.c:983
  __do_sys_exit_group kernel/exit.c:994 [inline]
  __se_sys_exit_group kernel/exit.c:992 [inline]
  __x64_sys_exit_group+0x44/0x50 kernel/exit.c:992
  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x43ed68
Code: Bad RIP value.
RSP: 002b:00007ffc2b7b93f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043ed68
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004be568 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 00000000ffffffff R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d0180 R14: 0000000000000000 R15: 0000000000000000
==================================================================


---
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@googlegroups.com.

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

Re: KASAN: null-ptr-deref Write in rxrpc_unuse_local

[syzbot]

syzbot has bisected this bug to:

commit 5c2833938bf50d502586e16b9dad1e3cf88fda6f
Author: David Howells <dhowells@redhat.com>
Date:   Wed Jul 31 15:26:05 2019 +0000

     rxrpc: Fix local endpoint refcounting

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1519a11c600000
start commit:   87b983f5 Add linux-next specific files for 20190809
git tree:       linux-next
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1719a11c600000
console output: https://syzkaller.appspot.com/x/log.txt?x=1319a11c600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=28eea330e11df0eb
dashboard link: https://syzkaller.appspot.com/bug?extid=20dee719a2e090427b5f
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17ceae36600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10ebc40e600000

Reported-by: syzbot+20dee719a2e090427b5f@syzkaller.appspotmail.com
Fixes: 5c2833938bf5 ("rxrpc: Fix local endpoint refcounting")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection