linux-kernel - Re: USB: hub: Delete an error message for a failed memory allocation in usb_hub_clear_tt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMuHMdUJMBS2Hwfc69MsOPk=8FxRs=45pp5TRsJdPUhQYDm+5A@mail.gmail.com>
Date:   Thu, 7 Dec 2017 09:45:38 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        SF Markus Elfring <elfring@...rs.sourceforge.net>,
        USB list <linux-usb@...r.kernel.org>,
        Joe Perches <joe@...ches.com>,
        Daniel Drake <drake@...lessm.com>,
        Dmitry Fleytman <dmitry@...nix.com>,
        Eugene Korenevsky <ekorenevsky@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Günter Röck <linux@...ck-us.net>,
        Johan Hovold <johan@...nel.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Peter Chen <peter.chen@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: USB: hub: Delete an error message for a failed memory allocation
 in usb_hub_clear_tt_buffer()

Hi Dan,

On Thu, Dec 7, 2017 at 9:35 AM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
> On Thu, Dec 07, 2017 at 08:40:07AM +0100, Geert Uytterhoeven wrote:
>> On Wed, Dec 6, 2017 at 11:02 PM, Alan Stern <stern@...land.harvard.edu> wrote:
>> > On Wed, 6 Dec 2017, SF Markus Elfring wrote:
>> >> >>> Does the existing memory allocation error message include the
>> >> >>> &udev->dev device name and driver name?  If it doesn't, there will be
>> >> >>> no way for the user to tell that the error message is related to the
>> >> >>> device failure.
>> >> >>
>> >> >> No, but the effect is similar.
>> >> >>
>> >> >> OOM does a dump_stack() so this function's call tree is shown.
>> >> >
>> >> > A call stack doesn't tell you which device was being handled.
>> >>
>> >> Do you find a default Linux allocation failure report insufficient then?
>> >>
>> >> Would you like to to achieve that the requested information can be determined
>> >> from a backtrace?
>> >
>> > It is not practical to do this.  The memory allocation routines do not
>> > for what purpose the memory is being allocated; hence when a failure
>> > occurs they cannot tell what device (or other part of the system) will
>> > be affected.
>>
>> If even allocation of 24 bytes fails, lots of other devices and other parts of
>> the system will start failing really soon...
>
> Small allocations never fail in the current kernel.

A few comments (this is in response to a patch from Markus, so there have
to be lots of questions and uncertainties ;-)
1. In the current kernel. What about the future?
2. If a small allocation cannot fail, what happens if the small memory slab
   is exhausted? A new page must be allocated, which will trigger an OOM,
   and some other part of the system will be killed and fail.
3. This driver uses GFP_ATOMIC, is that guaranteed to succeed? I think not.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds