Date:   Sun, 1 Apr 2018 13:46:30 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>,
        syzkaller-bugs@...glegroups.com,
        syzbot+84371b6062cb639d797e@...kaller.appspotmail.com
Subject: Re: WARNING: refcount bug in should_fail

On Sun, Apr 1, 2018 at 1:30 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Sun, Apr 1, 2018 at 1:11 PM, Tetsuo Handa
> <penguin-kernel@...ove.sakura.ne.jp> wrote:
>> Dmitry Vyukov wrote:
>>> On Sun, Apr 1, 2018 at 12:32 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>> > On Sun, Mar 4, 2018 at 6:57 AM, Tetsuo Handa
>>> > <penguin-kernel@...ove.sakura.ne.jp> wrote:
>>> >> Switching from mm to fsdevel, for this report says that put_net(net) in
>>> >> rpc_kill_sb() made net->count < 0 when mount_ns() failed due to
>>> >> register_shrinker() failure.
>>> >>
>>> >> Relevant commits will be
>>> >> commit 9ee332d99e4d5a97 ("sget(): handle failures of register_shrinker()") and
>>> >> commit d91ee87d8d85a080 ("vfs: Pass data, ns, and ns->userns to mount_ns.").
>>> >>
>>> >> When sget_userns() in mount_ns() failed, mount_ns() returns an error code to
>>> >> the caller without calling fill_super(). That is, get_net(sb->s_fs_info) was
>>> >> not called by rpc_fill_super() (via fill_super callback passed to mount_ns())
>>> >> but put_net(sb->s_fs_info) is called by rpc_kill_sb() (via fs->kill_sb() from
>>> >> deactivate_locked_super()).
>>> >>
>>> >> ----------
>>> >> static struct dentry *
>>> >> rpc_mount(struct file_system_type *fs_type,
>>> >>                 int flags, const char *dev_name, void *data)
>>> >> {
>>> >>         struct net *net = current->nsproxy->net_ns;
>>> >>         return mount_ns(fs_type, flags, data, net, net->user_ns, rpc_fill_super);
>>> >> }
>>> >> ----------
>>> >
>>> > Messed kernel output, this is definitely not in should_fail.
>>> >
>>> > #syz dup: WARNING: refcount bug in sk_alloc
>>>
>>> Please don't drop reporter (syzbot) email from CC.
>>>
>>> #syz dup: WARNING: refcount bug in sk_alloc
>>>
>>
>> Excuse me? This "refcount bug in should_fail" is talking about sget_userns() versus rpc_fill_super().
>> I think we need to fix either 9ee332d99e4d5a97 or d91ee87d8d85a080.
>
> Hi,
>
> I think I was looking at this incarnation of this bug before marking it as dup:
> https://syzkaller.appspot.com/text?tag=CrashReport&id=5246446760624128
> that report in fact includes sk_alloc frame. Kernel turning crash
> reports into untangleable mess is not really helpful.
>
> I will undup this into an independent bug.
> It's just that we don't have such functionality yet, so I need to
> implement it first.

This is now implemented:
https://github.com/google/syzkaller/commit/0a78e248b7b6537ccdf66dc8806d76e0a97efe21
Let's try it:

#syz undup



>>> >> syzbot wrote:
>>> >>> Hello,
>>> >>>
>>> >>> syzbot hit the following crash on bpf-next commit
>>> >>> 6f1b5a2b58d8470e5a8b25ab29f5fdb4616ffff8 (Tue Feb 27 04:11:23 2018 +0000)
>>> >>> Merge branch 'bpf-kselftest-improvements'
>>> >>>
>>> >>> C reproducer is attached.
>>> >>> syzkaller reproducer is attached.
>>> >>> Raw console output is attached.
>>> >>> compiler: gcc (GCC) 7.1.1 20170620
>>> >>> .config is attached.
>>> >>>
>>> >>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> >>> Reported-by: syzbot+84371b6062cb639d797e@...kaller.appspotmail.com
>>> >>> 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.
>>> >>>
>>> >>> ------------[ cut here ]------------
>>> >>> FAULT_INJECTION: forcing a failure.
>>> >>> name failslab, interval 1, probability 0, space 0, times 0
>>> >>> refcount_t: underflow; use-after-free.
>>> >>> CPU: 1 PID: 4239 Comm: syzkaller149381 Not tainted 4.16.0-rc2+ #20
>>> >>> WARNING: CPU: 0 PID: 4237 at lib/refcount.c:187
>>> >>> refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187
>>> >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>>> >>> Google 01/01/2011
>>> >>> Call Trace:
>>> >>> Kernel panic - not syncing: panic_on_warn set ...
>>> >>>
>>> >>>   __dump_stack lib/dump_stack.c:17 [inline]
>>> >>>   dump_stack+0x194/0x24d lib/dump_stack.c:53
>>> >>>   fail_dump lib/fault-inject.c:51 [inline]
>>> >>>   should_fail+0x8c0/0xa40 lib/fault-inject.c:149
>>> >>>   should_failslab+0xec/0x120 mm/failslab.c:32
>>> >>>   slab_pre_alloc_hook mm/slab.h:422 [inline]
>>> >>>   slab_alloc mm/slab.c:3365 [inline]
>>> >>>   __do_kmalloc mm/slab.c:3703 [inline]
>>> >>>   __kmalloc+0x63/0x760 mm/slab.c:3714
>>> >>>   kmalloc include/linux/slab.h:517 [inline]
>>> >>>   kzalloc include/linux/slab.h:701 [inline]
>>> >>>   register_shrinker+0x10e/0x2d0 mm/vmscan.c:268
>>> >>>   sget_userns+0xbbf/0xe40 fs/super.c:520
>>> >>>   mount_ns+0x6d/0x190 fs/super.c:1029
>>> >>>   rpc_mount+0x9e/0xd0 net/sunrpc/rpc_pipe.c:1451
>>> >>>   mount_fs+0x66/0x2d0 fs/super.c:1222
>>> >>>   vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037
>>> >>>   vfs_kern_mount fs/namespace.c:2509 [inline]
>>> >>>   do_new_mount fs/namespace.c:2512 [inline]
>>> >>>   do_mount+0xea4/0x2bb0 fs/namespace.c:2842
>>> >>>   SYSC_mount fs/namespace.c:3058 [inline]
>>> >>>   SyS_mount+0xab/0x120 fs/namespace.c:3035
>>> >>>   do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287
>>> >>>   entry_SYSCALL_64_after_hwframe+0x42/0xb7
>>> >>> RIP: 0033:0x4460f9
>>> >>> RSP: 002b:00007fbcd769ad78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
>>> >>> RAX: ffffffffffffffda RBX: 00000000006dcc6c RCX: 00000000004460f9
>>> >>> RDX: 0000000020000080 RSI: 0000000020000040 RDI: 0000000020000000
>>> >>> RBP: 00007fbcd769ad80 R08: 00000000200000c0 R09: 0000000000003131
>>> >>> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc68
>>> >>> R13: ffffffffffffffff R14: 0000000000000037 R15: 0030656c69662f2e
>>> >>> CPU: 0 PID: 4237 Comm: syzkaller149381 Not tainted 4.16.0-rc2+ #20
>>> >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>>> >>> Google 01/01/2011
>>> >>> Call Trace:
>>> >>>   __dump_stack lib/dump_stack.c:17 [inline]
>>> >>>   dump_stack+0x194/0x24d lib/dump_stack.c:53
>>> >>>   panic+0x1e4/0x41c kernel/panic.c:183
>>> >>>   __warn+0x1dc/0x200 kernel/panic.c:547
>>> >>>   report_bug+0x211/0x2d0 lib/bug.c:184
>>> >>>   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
>>> >>>   do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
>>> >>>   invalid_op+0x58/0x80 arch/x86/entry/entry_64.S:957
>>> >>> RIP: 0010:refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187
>>> >>> RSP: 0018:ffff8801b164f6d8 EFLAGS: 00010286
>>> >>> RAX: dffffc0000000008 RBX: 0000000000000000 RCX: ffffffff815ac30e
>>> >>> RDX: 0000000000000000 RSI: 1ffff100362c9e8b RDI: 1ffff100362c9e60
>>> >>> RBP: ffff8801b164f768 R08: 0000000000000000 R09: 0000000000000000
>>> >>> R10: ffff8801b164f610 R11: 0000000000000000 R12: 1ffff100362c9edc
>>> >>> R13: 00000000ffffffff R14: 0000000000000001 R15: ffff8801ae924044
>>> >>>   refcount_dec_and_test+0x1a/0x20 lib/refcount.c:212
>>> >>>   put_net include/net/net_namespace.h:220 [inline]
>>> >>>   rpc_kill_sb+0x253/0x3c0 net/sunrpc/rpc_pipe.c:1473
>>> >>>   deactivate_locked_super+0x88/0xd0 fs/super.c:312
>>> >>>   sget_userns+0xbda/0xe40 fs/super.c:522
>>> >>>   mount_ns+0x6d/0x190 fs/super.c:1029
>>> >>>   rpc_mount+0x9e/0xd0 net/sunrpc/rpc_pipe.c:1451
>>> >>>   mount_fs+0x66/0x2d0 fs/super.c:1222
>>> >>>   vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037
>>> >>>   vfs_kern_mount fs/namespace.c:2509 [inline]
>>> >>>   do_new_mount fs/namespace.c:2512 [inline]
>>> >>>   do_mount+0xea4/0x2bb0 fs/namespace.c:2842
>>> >>>   SYSC_mount fs/namespace.c:3058 [inline]
>>> >>>   SyS_mount+0xab/0x120 fs/namespace.c:3035
>>> >>>   do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287
>>> >>>   entry_SYSCALL_64_after_hwframe+0x42/0xb7
>>> >>> RIP: 0033:0x4460f9
>>> >>> RSP: 002b:00007fbcd76dcd78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
>>> >>> RAX: ffffffffffffffda RBX: 00000000006dcc3c RCX: 00000000004460f9
>>> >>> RDX: 0000000020000080 RSI: 0000000020000040 RDI: 0000000020000000
>>> >>> RBP: 00007fbcd76dcd80 R08: 00000000200000c0 R09: 0000000000003131
>>> >>> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc38
>>> >>> R13: ffffffffffffffff R14: 0000000000000028 R15: 0030656c69662f2e
>>> >>> 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 syzkaller@...glegroups.com.
>>> >>>
>>> >>> 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
>>> >>> If you want to test a patch for this bug, please reply with:
>>> >>> #syz test: git://repo/address.git branch
>>> >>> and provide the patch inline or as an attachment.
>>> >>> To mark this as a duplicate of another syzbot report, please reply with:
>>> >>> #syz dup: exact-subject-of-another-report
>>> >>> If it's a one-off invalid bug report, please reply with:
>>> >>> #syz invalid
>>> >>> Note: if the crash happens again, it will cause creation of a new bug
>>> >>> report.
>>> >>> Note: all commands must start from beginning of the line in the email body.
>>> >>>
>>> >>
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>>
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