netdev - Re: WARNING in sysfs_warn

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Date:   Mon, 22 Jan 2018 16:04:45 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     syzbot 
        <bot+1fdad4e2731bf0c1bc19953ccc5061237ec92783@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com,
        David Miller <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        jakub.kicinski@...ronome.com,
        Willem de Bruijn <willemb@...gle.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        John Fastabend <john.fastabend@...il.com>,
        "Tobin C. Harding" <me@...in.cc>, netdev <netdev@...r.kernel.org>,
        linux-wireless@...r.kernel.org
Subject: Re: WARNING in sysfs_warn_dup

On Mon, Jan 22, 2018 at 3:45 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Mon, Jan 22, 2018 at 03:30:12PM +0100, Dmitry Vyukov wrote:
>> On Mon, Jan 22, 2018 at 3:00 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
>> > On Mon, Jan 22, 2018 at 02:47:33PM +0100, Dmitry Vyukov wrote:
>> >> On Tue, Dec 19, 2017 at 10:06 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> >> > On Tue, Dec 19, 2017 at 10:03 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> >> >>
>> >> >> On Tue, Dec 19, 2017 at 10:01 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
>> >> >>>
>> >> >>> On Mon, Dec 18, 2017 at 08:57:01AM -0800, syzbot wrote:
>> >> >>> > Hello,
>> >> >>> >
>> >> >>> > syzkaller hit the following crash on
>> >> >>> > 6084b576dca2e898f5c101baef151f7bfdbb606d
>> >> >>> > git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
>> >> >>> > compiler: gcc (GCC) 7.1.1 20170620
>> >> >>> > .config is attached
>> >> >>> > Raw console output is attached.
>> >> >>> >
>> >> >>> > Unfortunately, I don't have any reproducer for this bug yet.
>> >> >>> >
>> >> >>> >
>> >> >>> > netlink: 9 bytes leftover after parsing attributes in process
>> >> >>> > `syz-executor3'.
>> >> >>> > sg_write: data in/out 822404280/197 bytes for SCSI command 0x12-- guessing
>> >> >>> > data in;
>> >> >>> >    program syz-executor0 not setting count and/or reply_len properly
>> >> >>> > sg_write: data in/out 262364/161 bytes for SCSI command 0xff-- guessing data
>> >> >>> > in;
>> >> >>> >    program syz-executor0 not setting count and/or reply_len properly
>> >> >>> > WARNING: CPU: 1 PID: 22282 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x60/0x80
>> >> >>> > fs/sysfs/dir.c:30
>> >> >>> > Kernel panic - not syncing: panic_on_warn set ...
>> >> >>>
>> >> >>> Looks like a networking issue, it tried to create two sysfs directories
>> >> >>> with the same name, which isn't a sysfs bug :)
>> >> >
>> >> >
>> >> > Now as plain text:
>> >> >
>> >> > +net/core/dev.c maintainers
>> >>
>> >>
>> >> Also happens for wiphy_register (on upstream
>> >> a8750ddca918032d6349adbf9a4b6555e7db20da):
>> >>
>> >> ------------[ cut here ]------------
>> >> sysfs: cannot create duplicate filename
>> >> '/class/ieee80211/š§"ût{§Ôðô Š!× ž 7… Š†õiùS6 È< »þ {_CK5äá   ×ÝÊmô Be'
>> >
>> > That's a wonderful filename :)
>> >
>> >> WARNING: CPU: 1 PID: 8233 at fs/sysfs/dir.c:31
>> >> sysfs_warn_dup+0x7e/0xa0 fs/sysfs/dir.c:30
>> >
>> > As this is just sysfs saying "Hey dummy, you are trying to do something
>> > foolish here", what would be the better thing for it to do?
>> >
>> > Just printk(KERN_WARNING...) and then dump the stack?
>> >
>> > It seems the WARN_ON() that is currently being used is being treated as
>> > an "error" by your testing, when really it isn't, unless the caller can
>> > not handle the error being passed back up to it by the sysfs core.
>> > Which it should, but I don't think you are even giving it the chance as
>> > you are:
>> >
>> >> Kernel panic - not syncing: panic_on_warn set ...
>> >
>> > Yup, panic_on_warn :(
>> >
>> > ideas to make this easier for you?
>>
>>
>> pr_warn or pr_warn_once (optionally followed by dump_stack) would work
>> for syzbot.
>
> This shouldn't be a _once() call, as it is called by things all over the
> kernel, all with unique paths.
>
> I'll go make up a patch for this, thanks.

#syz fix: sysfs: turn WARN() into pr_warn()