Messages in this thread | | | Date | Tue, 3 Nov 2020 08:57:26 +0000 | From | Lee Jones <> | Subject | Re: [PATCH 1/2] misc: c2port: core: Make copying name from userspace more secure |
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On Mon, 02 Nov 2020, Rodolfo Giometti wrote:
> On 02/11/2020 14:47, Lee Jones wrote: > > On Mon, 02 Nov 2020, gregkh@linuxfoundation.org wrote: > > > >> On Mon, Nov 02, 2020 at 12:43:01PM +0000, Lee Jones wrote: > >>> On Mon, 02 Nov 2020, gregkh@linuxfoundation.org wrote: > >>> > >>>> On Mon, Nov 02, 2020 at 11:49:03AM +0000, Lee Jones wrote: > >>>>> On Mon, 02 Nov 2020, David Laight wrote: > >>>>> > >>>>>> From: Lee Jones > >>>>>>> Sent: 02 November 2020 11:12 > >>>>>>> > >>>>>>> strncpy() may not provide a NUL terminator, which means that a 1-byte > >>>>>>> leak would be possible *if* this was ever copied to userspace. Ensure > >>>>>>> the buffer will always be NUL terminated by using the kernel's > >>>>>>> strscpy() which a) uses the destination (instead of the source) size > >>>>>>> as the bytes to copy and b) is *always* NUL terminated. > >>>>>>> > >>>>>>> Cc: Rodolfo Giometti <giometti@enneenne.com> > >>>>>>> Cc: "Eurotech S.p.A" <info@eurotech.it> > >>>>>>> Reported-by: Geert Uytterhoeven <geert+renesas@glider.be> > >>>>>>> Acked-by: Arnd Bergmann <arnd@arndb.de> > >>>>>>> Signed-off-by: Lee Jones <lee.jones@linaro.org> > >>>>>>> --- > >>>>>>> drivers/misc/c2port/core.c | 2 +- > >>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) > >>>>>>> > >>>>>>> diff --git a/drivers/misc/c2port/core.c b/drivers/misc/c2port/core.c > >>>>>>> index 80d87e8a0bea9..b96444ec94c7e 100644 > >>>>>>> --- a/drivers/misc/c2port/core.c > >>>>>>> +++ b/drivers/misc/c2port/core.c > >>>>>>> @@ -923,7 +923,7 @@ struct c2port_device *c2port_device_register(char *name, > >>>>>>> } > >>>>>>> dev_set_drvdata(c2dev->dev, c2dev); > >>>>>>> > >>>>>>> - strncpy(c2dev->name, name, C2PORT_NAME_LEN - 1); > >>>>>>> + strscpy(c2dev->name, name, sizeof(c2dev->name)); > >>>>>> > >>>>>> strscpy() doesn't zero fill so if the memory isn't zeroed > >>>>>> and a 'blind' copy to user of the structure is done > >>>>>> then more data is leaked. > >>>>>> > >>>>>> strscpy() may be better, but rational isn't right. > >>>>> > >>>>> The original patch zeroed the data too, but I was asked to remove that > >>>>> part [0]. In your opinion, should it be reinstated? > >>>>> > >>>>> [0] https://lore.kernel.org/patchwork/patch/1272290/ > >>>> > >>>> Just keep the kzalloc() part of the patch, this portion makes no sense > >>>> to me. > >>> > >>> Can do. > >>> > >>>> But if you REALLY want to get it correct, call dev_set_name() > >>>> instead please, as that is what it is there for. > >>> > >>> The line above isn't setting the 'struct device' name. It looks as > >>> though 'struct c2port' has it's own member, also called 'name'. As to > >>> how they differ, I'm not currently aware. Nor do I wish to mess > >>> around with the semantics all that much. > >>> > >>> Going with suggestion #1. > >> > >> As the "device" already has a name, I suggest just getting rid of this > >> name field anyway, no need for duplicates. > > > > That definitely goes against the point I made above: > > > > "Nor do I wish to mess around with the semantics all that much." > > > > It looks as though the device name 'c2port%d' varies greatly to the > > requested name 'uc'. I don't have enough knowledge of how user- > > space expects to use the provided sysfs entries to be able to > > competently merge/decide which of these should be kept and which to > > discard. > > > > Hopefully one of the authors/maintainers are reading this and can come > > up with an acceptable solution. > > User-space usage can change its behavior so, please, consider the best solution > from the kernel space point-of-view. :)
If you're sure, I can add it to my TODO.
-- Lee Jones [李琼斯] Senior Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog
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