netdev - Re: WARNING in sysfs_warn

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Date:   Mon, 22 Jan 2018 15:30:12 +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 3:00 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.

Thanks!