Re: [REGRESSION] changes to driver_override parsing broke DPDK script

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Aug 10, 2022 at 08:11:33AM +0200, Greg KH wrote:
> On Wed, Aug 10, 2022 at 08:54:36AM +0300, Krzysztof Kozlowski wrote:
> > On 09/08/2022 22:21, Bjorn Helgaas wrote:
> > > [+cc regressions list]
> > > 
> > > 23d99baf9d72 appeared in v5.19-rc1.
> > > 
> > > On Tue, Aug 09, 2022 at 11:29:43AM -0700, Stephen Hemminger wrote:
> > >> This commit broke the driver override script in DPDK.
> > >> This is an API/ABI breakage, please revert or fix the commit.
> > >>
> > >> Report of problem:
> > >> http://mails.dpdk.org/archives/dev/2022-August/247794.html
> > 
> > Thanks for the report. I'll take a look.
> > 
> > >>
> > >>
> > >> commit 23d99baf9d729ca30b2fb6798a7b403a37bfb800
> > >> Author: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> > >> Date:   Tue Apr 19 13:34:28 2022 +0200
> > >>
> > >>     PCI: Use driver_set_override() instead of open-coding
> > >>     
> > >>     Use a helper to set driver_override to the reduce amount of duplicated
> > >>     code.  Make the driver_override field const char, because it is not
> > >>     modified by the core and it matches other subsystems.
> > >>     
> > >>     Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> > >>     Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> > >>     Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> > >>     Link: https://lore.kernel.org/r/20220419113435.246203-6-krzysztof.kozlowski@linaro.org
> > >>     Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > >>
> > >>
> > >> The script is sending single nul character to remove override
> > >> and that no longer works.
> > 
> > The sysfs API clearly states:
> > "and
> >  may be cleared with an empty string (echo > driver_override)."
> > Documentation/ABI/testing/sysfs-bus-pci
> > 
> > Sending other data and expecting the same result is not conforming to
> > API. Therefore we have usual example of some undocumented behavior which
> > user-space started relying on and instead using API, user-space expect
> > that undocumented behavior to be back.
> > 
> > Yay! I wonder what is the point to even describe the ABI if user-space
> > can simply ignore it?
> 
> One can argue that a string of just '\0' is an "empty string" and we
> should be able to properly handle this in the kernel.  Heck,
> "\0\0\0\0\0\0" is also an "empty string", right?
> 
> I don't have an issue with fixing the kernel up here, it should be able
> to handle this.

Stephen, does the patch below fix this for you?

thanks,

greg k-h

-----------------

diff --git a/drivers/base/driver.c b/drivers/base/driver.c
index 15a75afe6b84..676b6275d5b5 100644
--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -63,6 +63,12 @@ int driver_set_override(struct device *dev, const char **override,
 	if (len >= (PAGE_SIZE - 1))
 		return -EINVAL;
 
+	/*
+	 * Compute the real length of the string in case userspace sends us a
+	 * bunch of \0 characters like python likes to do.
+	 */
+	len = strlen(s);
+
 	if (!len) {
 		/* Empty string passed - clear override */
 		device_lock(dev);