Subject: Re: WARNING in refcount_inc (3)

From: Eric Biggers <[email-masked]>
Date: Thu, 23 Aug 2018 00:24:36 -0700

On Thu, Apr 19, 2018 at 03:45:09PM -0700, Eric Biggers wrote:
> On Sat, Mar 31, 2018 at 04:01:02PM -0700, syzbot wrote:
> > Hello,
> > 
> > syzbot hit the following crash on bpf-next commit
> > 1379ef828a18d8f81c526b25e4d5685caa2cfd65 (Thu Mar 29 22:09:44 2018 +0000)
> > Merge branch 'bpf-sockmap-ingress'
> > syzbot dashboard link:
> > https://syzkaller.appspot.com/bug?extid=6eaf536fd743f5e119c5
> > 
> > So far this crash happened 6 times on bpf-next.
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?id=6614614900998144
> > syzkaller reproducer:
> > https://syzkaller.appspot.com/x/repro.syz?id=5035340528091136
> > Raw console output:
> > https://syzkaller.appspot.com/x/log.txt?id=5063394046509056
> > Kernel config:
> > https://syzkaller.appspot.com/x/.config?id=-1280663959502969741
> > compiler: gcc (GCC) 7.1.1 20170620
> > 
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: [email-masked]
> > It will help syzbot understand when the bug is fixed. See footer for
> > details.
> > If you forward the report, please keep this part and the footer.
> > 
> > R13: 0000000000000005 R14: 0000000000001380 R15: 00007ffd314c8768
> > ------------[ cut here ]------------
> > ------------[ cut here ]------------
> > refcount_t: increment on 0; use-after-free.
> > refcount_t: underflow; use-after-free.
> > WARNING: CPU: 1 PID: 4434 at lib/refcount.c:153 refcount_inc+0x47/0x50
> > lib/refcount.c:153
> > WARNING: CPU: 0 PID: 4437 at lib/refcount.c:187
> > refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187
> > Kernel panic - not syncing: panic_on_warn set ...
> > 
> > Modules linked in:
> > CPU: 1 PID: 4434 Comm: syzkaller349430 Not tainted 4.16.0-rc6+ #41
> > CPU: 0 PID: 4437 Comm: syzkaller349430 Not tainted 4.16.0-rc6+ #41
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > RIP: 0010:refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187
> > Call Trace:
> > RSP: 0018:ffff8801b061f728 EFLAGS: 00010286
> >  __dump_stack lib/dump_stack.c:17 [inline]
> >  dump_stack+0x194/0x24d lib/dump_stack.c:53
> > RAX: dffffc0000000008 RBX: 0000000000000000 RCX: ffffffff815ba4be
> > RDX: 0000000000000000 RSI: 1ffff100360c3e95 RDI: 1ffff100360c3e6a
> > RBP: ffff8801b061f7b8 R08: 0000000000000000 R09: 0000000000000000
> > R10: ffff8801b061f850 R11: 0000000000000000 R12: 1ffff100360c3ee6
> >  panic+0x1e4/0x41c kernel/panic.c:183
> > R13: 00000000ffffffff R14: 0000000000000001 R15: ffff8801b1be4184
> > FS:  0000000001817880(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007ffd314c9000 CR3: 00000001b04a1006 CR4: 00000000001606f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  __warn+0x1dc/0x200 kernel/panic.c:547
> >  report_bug+0x1f4/0x2b0 lib/bug.c:186
> >  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
> >  fixup_bug arch/x86/kernel/traps.c:247 [inline]
> >  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
> >  refcount_dec_and_test+0x1a/0x20 lib/refcount.c:212
> >  put_net include/net/net_namespace.h:222 [inline]
> >  __sk_destruct+0x560/0x920 net/core/sock.c:1592
> >  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
> >  invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:986
> > RIP: 0010:refcount_inc+0x47/0x50 lib/refcount.c:153
> > RSP: 0018:ffff8801b058f860 EFLAGS: 00010286
> > RAX: dffffc0000000008 RBX: ffff8801ab55a1c4 RCX: ffffffff815ba4be
> > RDX: 0000000000000000 RSI: 1ffff100360b1ebc RDI: 1ffff100360b1e91
> > RBP: ffff8801b058f868 R08: 0000000000000000 R09: 0000000000000000
> >  sk_destruct+0x47/0x80 net/core/sock.c:1601
> > R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801b058faf8
> >  __sk_free+0xf1/0x2b0 net/core/sock.c:1612
> > R13: ffff8801af87b513 R14: ffff8801ab55a1c0 R15: ffff8801af87b501
> >  sk_free+0x2a/0x40 net/core/sock.c:1623
> >  sock_put include/net/sock.h:1661 [inline]
> >  tcp_close+0x967/0x1190 net/ipv4/tcp.c:2329
> >  get_net include/net/net_namespace.h:204 [inline]
> >  sk_alloc+0x3f9/0x1440 net/core/sock.c:1540
> >  inet_release+0xed/0x1c0 net/ipv4/af_inet.c:427
> >  sock_release+0x8d/0x1e0 net/socket.c:594
> >  sock_close+0x16/0x20 net/socket.c:1149
> >  __fput+0x327/0x7e0 fs/file_table.c:209
> >  ____fput+0x15/0x20 fs/file_table.c:243
> >  task_work_run+0x199/0x270 kernel/task_work.c:113
> >  inet_create+0x47c/0xf50 net/ipv4/af_inet.c:320
> >  tracehook_notify_resume include/linux/tracehook.h:191 [inline]
> >  exit_to_usermode_loop+0x275/0x2f0 arch/x86/entry/common.c:166
> >  __sock_create+0x4d4/0x850 net/socket.c:1285
> >  prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
> >  syscall_return_slowpath arch/x86/entry/common.c:265 [inline]
> >  do_syscall_64+0x6ec/0x940 arch/x86/entry/common.c:292
> >  sock_create net/socket.c:1325 [inline]
> >  SYSC_socket net/socket.c:1355 [inline]
> >  SyS_socket+0xeb/0x1d0 net/socket.c:1335
> >  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
> >  entry_SYSCALL_64_after_hwframe+0x42/0xb7
> > RIP: 0033:0x402950
> > RSP: 002b:00007ffd314c8628 EFLAGS: 00000246
> >  ORIG_RAX: 0000000000000003
> > RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000402950
> > RDX: 00000000000000e0 RSI: 00007ffd314c8f00 RDI: 0000000000000003
> > RBP: 00007ffd314c8740 R08: 00007ffd314c864c R09: 0000000000000001
> > R10: 00007ffd314c8740 R11: 0000000000000246 R12: 00000000006cf4c0
> > R13: 00000000006cee40 R14: 0000000000001380 R15: 00007ffd314c8768
> > Code:
> >  entry_SYSCALL_64_after_hwframe+0x42/0xb7
> > 5e
> > RIP: 0033:0x4456a7
> > 41
> > RSP: 002b:00007ffd314c8628 EFLAGS: 00000202 ORIG_RAX: 0000000000000029
> > 5f
> > RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00000000004456a7
> > 5d
> > RDX: 0000000000000006 RSI: 0000000000000001 RDI: 0000000000000002
> > RBP: 00007ffd314c8740 R08: 0000000000000000 R09: 0000000000000001
> > c3
> > R10: 0000000000000006 R11: 0000000000000202 R12: 0000000000000003
> > e8
> > R13: 0000000000000003 R14: 0000000000006cc2 R15: 00007ffd314c8768
> > 0a 0b be fe 80 3d 20 c9 84 05 00 75 1a e8 fc 0a be fe 48 c7 c7 e0 78 e5 86
> > c6 05 0b c9 84 05 01 e8 a9 16 8e fe <0f> 0b 31 db eb a3 e8 de 0a be fe 83 fb
> > ff 0f 85 63 ff ff ff 31
> > ---[ end trace dd327356f543ce46 ]---
> > Dumping ftrace buffer:
> >    (ftrace buffer empty)
> > Kernel Offset: disabled
> > Rebooting in 86400 seconds..
> > 
> > 
> > ---
> > This bug is generated by a dumb bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for details.
> > Direct all questions to [email-masked].
> > 
> > syzbot will keep track of this bug report.
> > If you forgot to add the Reported-by tag, once the fix for this bug is
> > merged
> > into any tree, please reply to this email with:
> > #syz fix: exact-commit-title
> 
> Broken error handling when mounting rpc_pipefs is messing things up.
> Fixed by patch in vfs/for-linus:
> 
> #syz fix: rpc_pipefs: deal with early sget() failures
> 

Correction: the patch I mentioned above was dropped, and the fix for this that
actually went upstream was commit 8e04944f0ea8b83:

#syz fix: mm,vmscan: Allow preallocating memory for register_shrinker().

- Eric