[PATCH] hamradio: replace deprecated strncpy with strscpy

[PATCH] hamradio: replace deprecated strncpy with strscpy

[Justin Stitt]

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect both hi.data.modename and hi.data.drivername to be
NUL-terminated but not necessarily NUL-padded which is evident by its
usage with sprintf:
|       sprintf(hi.data.modename, "%sclk,%smodem,fclk=%d,bps=%d%s",
|               bc->cfg.intclk ? "int" : "ext",
|               bc->cfg.extmodem ? "ext" : "int", bc->cfg.fclk, bc->cfg.bps,
|               bc->cfg.loopback ? ",loopback" : "");

Note that this data is copied out to userspace with:
|       if (copy_to_user(data, &hi, sizeof(hi)))
... however, the data was also copied FROM the user here:
|       if (copy_from_user(&hi, data, sizeof(hi)))

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.

Also, there are 33 instances of trailing whitespace in this file alone.
I've opted to not remove them in this patch.
---
 drivers/net/hamradio/baycom_epp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/hamradio/baycom_epp.c b/drivers/net/hamradio/baycom_epp.c
index 83ff882f5d97..30a0fbb12b9c 100644
--- a/drivers/net/hamradio/baycom_epp.c
+++ b/drivers/net/hamradio/baycom_epp.c
@@ -1074,7 +1074,7 @@ static int baycom_siocdevprivate(struct net_device *dev, struct ifreq *ifr,
 		return 0;
 
 	case HDLCDRVCTL_DRIVERNAME:
-		strncpy(hi.data.drivername, "baycom_epp", sizeof(hi.data.drivername));
+		strscpy(hi.data.drivername, "baycom_epp", sizeof(hi.data.drivername));
 		break;
 		
 	case HDLCDRVCTL_GETMODE:
@@ -1091,7 +1091,7 @@ static int baycom_siocdevprivate(struct net_device *dev, struct ifreq *ifr,
 		return baycom_setmode(bc, hi.data.modename);
 
 	case HDLCDRVCTL_MODELIST:
-		strncpy(hi.data.modename, "intclk,extclk,intmodem,extmodem,divider=x",
+		strscpy(hi.data.modename, "intclk,extclk,intmodem,extmodem,divider=x",
 			sizeof(hi.data.modename));
 		break;
 

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231012-strncpy-drivers-net-hamradio-baycom_epp-c-6e11c9483b9f

Best regards,
--
Justin Stitt <justinstitt@google.com>

Re: [PATCH] hamradio: replace deprecated strncpy with strscpy

[Simon Horman]

On Thu, Oct 12, 2023 at 09:33:32PM +0000, Justin Stitt wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> We expect both hi.data.modename and hi.data.drivername to be
> NUL-terminated but not necessarily NUL-padded which is evident by its
> usage with sprintf:
> |       sprintf(hi.data.modename, "%sclk,%smodem,fclk=%d,bps=%d%s",
> |               bc->cfg.intclk ? "int" : "ext",
> |               bc->cfg.extmodem ? "ext" : "int", bc->cfg.fclk, bc->cfg.bps,
> |               bc->cfg.loopback ? ",loopback" : "");
> 
> Note that this data is copied out to userspace with:
> |       if (copy_to_user(data, &hi, sizeof(hi)))
> ... however, the data was also copied FROM the user here:
> |       if (copy_from_user(&hi, data, sizeof(hi)))

Thanks Justin,

I see that too.

Perhaps I am off the mark here, and perhaps it's out of scope for this
patch, but I do think it would be nicer if the kernel only sent
intended data to user-space, even if any unintended payload came
from user-space.

> Considering the above, a suitable replacement is `strscpy` [2] due to
> the fact that it guarantees NUL-termination on the destination buffer
> without unnecessarily NUL-padding.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

...

Re: [PATCH] hamradio: replace deprecated strncpy with strscpy

[Dan Carpenter]

On Sun, Oct 15, 2023 at 05:06:19PM +0200, Simon Horman wrote:
> On Thu, Oct 12, 2023 at 09:33:32PM +0000, Justin Stitt wrote:
> > strncpy() is deprecated for use on NUL-terminated destination strings
> > [1] and as such we should prefer more robust and less ambiguous string
> > interfaces.
> > 
> > We expect both hi.data.modename and hi.data.drivername to be
> > NUL-terminated but not necessarily NUL-padded which is evident by its
> > usage with sprintf:
> > |       sprintf(hi.data.modename, "%sclk,%smodem,fclk=%d,bps=%d%s",
> > |               bc->cfg.intclk ? "int" : "ext",
> > |               bc->cfg.extmodem ? "ext" : "int", bc->cfg.fclk, bc->cfg.bps,
> > |               bc->cfg.loopback ? ",loopback" : "");
> > 
> > Note that this data is copied out to userspace with:
> > |       if (copy_to_user(data, &hi, sizeof(hi)))
> > ... however, the data was also copied FROM the user here:
> > |       if (copy_from_user(&hi, data, sizeof(hi)))
> 
> Thanks Justin,
> 
> I see that too.
> 
> Perhaps I am off the mark here, and perhaps it's out of scope for this
> patch, but I do think it would be nicer if the kernel only sent
> intended data to user-space, even if any unintended payload came
> from user-space.
> 

It's kind of normal to pass user space data back to itself.  We
generally only worry about info leaks.

regards,
dan carpenter

Re: [PATCH] hamradio: replace deprecated strncpy with strscpy

[Kees Cook]

On October 15, 2023 10:47:53 PM PDT, Dan Carpenter <dan.carpenter@linaro.org> wrote:
>On Sun, Oct 15, 2023 at 05:06:19PM +0200, Simon Horman wrote:
>> On Thu, Oct 12, 2023 at 09:33:32PM +0000, Justin Stitt wrote:
>> > strncpy() is deprecated for use on NUL-terminated destination strings
>> > [1] and as such we should prefer more robust and less ambiguous string
>> > interfaces.
>> > 
>> > We expect both hi.data.modename and hi.data.drivername to be
>> > NUL-terminated but not necessarily NUL-padded which is evident by its
>> > usage with sprintf:
>> > |       sprintf(hi.data.modename, "%sclk,%smodem,fclk=%d,bps=%d%s",
>> > |               bc->cfg.intclk ? "int" : "ext",
>> > |               bc->cfg.extmodem ? "ext" : "int", bc->cfg.fclk, bc->cfg.bps,
>> > |               bc->cfg.loopback ? ",loopback" : "");
>> > 
>> > Note that this data is copied out to userspace with:
>> > |       if (copy_to_user(data, &hi, sizeof(hi)))
>> > ... however, the data was also copied FROM the user here:
>> > |       if (copy_from_user(&hi, data, sizeof(hi)))
>> 
>> Thanks Justin,
>> 
>> I see that too.
>> 
>> Perhaps I am off the mark here, and perhaps it's out of scope for this
>> patch, but I do think it would be nicer if the kernel only sent
>> intended data to user-space, even if any unintended payload came
>> from user-space.
>> 
>
>It's kind of normal to pass user space data back to itself.  We
>generally only worry about info leaks.

True but since this used to zero the rest of the buffet, let's just keep that behavior and use strscpy_pad().

-Kees

-- 
Kees Cook

Re: [PATCH] hamradio: replace deprecated strncpy with strscpy

[Kees Cook]

On October 16, 2023 10:01:20 AM PDT, Kees Cook <kees@kernel.org> wrote:
>
>
>On October 15, 2023 10:47:53 PM PDT, Dan Carpenter <dan.carpenter@linaro.org> wrote:
>>On Sun, Oct 15, 2023 at 05:06:19PM +0200, Simon Horman wrote:
>>> On Thu, Oct 12, 2023 at 09:33:32PM +0000, Justin Stitt wrote:
>>> > strncpy() is deprecated for use on NUL-terminated destination strings
>>> > [1] and as such we should prefer more robust and less ambiguous string
>>> > interfaces.
>>> > 
>>> > We expect both hi.data.modename and hi.data.drivername to be
>>> > NUL-terminated but not necessarily NUL-padded which is evident by its
>>> > usage with sprintf:
>>> > |       sprintf(hi.data.modename, "%sclk,%smodem,fclk=%d,bps=%d%s",
>>> > |               bc->cfg.intclk ? "int" : "ext",
>>> > |               bc->cfg.extmodem ? "ext" : "int", bc->cfg.fclk, bc->cfg.bps,
>>> > |               bc->cfg.loopback ? ",loopback" : "");
>>> > 
>>> > Note that this data is copied out to userspace with:
>>> > |       if (copy_to_user(data, &hi, sizeof(hi)))
>>> > ... however, the data was also copied FROM the user here:
>>> > |       if (copy_from_user(&hi, data, sizeof(hi)))
>>> 
>>> Thanks Justin,
>>> 
>>> I see that too.
>>> 
>>> Perhaps I am off the mark here, and perhaps it's out of scope for this
>>> patch, but I do think it would be nicer if the kernel only sent
>>> intended data to user-space, even if any unintended payload came
>>> from user-space.
>>> 
>>
>>It's kind of normal to pass user space data back to itself.  We
>>generally only worry about info leaks.
>
>True but since this used to zero the rest of the buffet, let's just keep that behavior and use strscpy_pad().

I'm calling all byte arrays a "buffet" from now on. ;)

-- 
Kees Cook

Re: [PATCH] hamradio: replace deprecated strncpy with strscpy

[Hugh Blemings]

On 17/10/23 04:03, Kees Cook wrote:
> 
> 
> On October 16, 2023 10:01:20 AM PDT, Kees Cook <kees@kernel.org> wrote:
>>
>>
>> On October 15, 2023 10:47:53 PM PDT, Dan Carpenter <dan.carpenter@linaro.org> wrote:
>>> On Sun, Oct 15, 2023 at 05:06:19PM +0200, Simon Horman wrote:
>>>> On Thu, Oct 12, 2023 at 09:33:32PM +0000, Justin Stitt wrote:
>>>>> strncpy() is deprecated for use on NUL-terminated destination strings
>>>>> [1] and as such we should prefer more robust and less ambiguous string
>>>>> interfaces.
>>>>>
>>>>> We expect both hi.data.modename and hi.data.drivername to be
>>>>> NUL-terminated but not necessarily NUL-padded which is evident by its
>>>>> usage with sprintf:
>>>>> |       sprintf(hi.data.modename, "%sclk,%smodem,fclk=%d,bps=%d%s",
>>>>> |               bc->cfg.intclk ? "int" : "ext",
>>>>> |               bc->cfg.extmodem ? "ext" : "int", bc->cfg.fclk, bc->cfg.bps,
>>>>> |               bc->cfg.loopback ? ",loopback" : "");
>>>>>
>>>>> Note that this data is copied out to userspace with:
>>>>> |       if (copy_to_user(data, &hi, sizeof(hi)))
>>>>> ... however, the data was also copied FROM the user here:
>>>>> |       if (copy_from_user(&hi, data, sizeof(hi)))
>>>>
>>>> Thanks Justin,
>>>>
>>>> I see that too.
>>>>
>>>> Perhaps I am off the mark here, and perhaps it's out of scope for this
>>>> patch, but I do think it would be nicer if the kernel only sent
>>>> intended data to user-space, even if any unintended payload came
>>>> from user-space.
>>>>
>>>
>>> It's kind of normal to pass user space data back to itself.  We
>>> generally only worry about info leaks.
>>
>> True but since this used to zero the rest of the buffet, let's just keep that behavior and use strscpy_pad().
> 
> I'm calling all byte arrays a "buffet" from now on. ;)
> 
A tasteful change to the sauce I think.  ;)

Re: [PATCH] hamradio: replace deprecated strncpy with strscpy

[Justin Stitt]

On Mon, Oct 16, 2023 at 3:18 PM Hugh Blemings <hugh@blemings.org> wrote:
>
>
>
> On 17/10/23 04:03, Kees Cook wrote:
> >
> >
> > On October 16, 2023 10:01:20 AM PDT, Kees Cook <kees@kernel.org> wrote:
> >>
> >>
> >> On October 15, 2023 10:47:53 PM PDT, Dan Carpenter <dan.carpenter@linaro.org> wrote:
> >>> On Sun, Oct 15, 2023 at 05:06:19PM +0200, Simon Horman wrote:
> >>>> On Thu, Oct 12, 2023 at 09:33:32PM +0000, Justin Stitt wrote:
> >>>>> strncpy() is deprecated for use on NUL-terminated destination strings
> >>>>> [1] and as such we should prefer more robust and less ambiguous string
> >>>>> interfaces.
> >>>>>
> >>>>> We expect both hi.data.modename and hi.data.drivername to be
> >>>>> NUL-terminated but not necessarily NUL-padded which is evident by its
> >>>>> usage with sprintf:
> >>>>> |       sprintf(hi.data.modename, "%sclk,%smodem,fclk=%d,bps=%d%s",
> >>>>> |               bc->cfg.intclk ? "int" : "ext",
> >>>>> |               bc->cfg.extmodem ? "ext" : "int", bc->cfg.fclk, bc->cfg.bps,
> >>>>> |               bc->cfg.loopback ? ",loopback" : "");
> >>>>>
> >>>>> Note that this data is copied out to userspace with:
> >>>>> |       if (copy_to_user(data, &hi, sizeof(hi)))
> >>>>> ... however, the data was also copied FROM the user here:
> >>>>> |       if (copy_from_user(&hi, data, sizeof(hi)))
> >>>>
> >>>> Thanks Justin,
> >>>>
> >>>> I see that too.
> >>>>
> >>>> Perhaps I am off the mark here, and perhaps it's out of scope for this
> >>>> patch, but I do think it would be nicer if the kernel only sent
> >>>> intended data to user-space, even if any unintended payload came
> >>>> from user-space.
> >>>>
> >>>
> >>> It's kind of normal to pass user space data back to itself.  We
> >>> generally only worry about info leaks.
> >>
> >> True but since this used to zero the rest of the buffet, let's just keep that behavior and use strscpy_pad().
> >
> > I'm calling all byte arrays a "buffet" from now on. ;)
> >
> A tasteful change to the sauce I think.  ;)

Just perfect that this is happening on a **ham**radio driver.