From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f48.google.com ([209.85.218.48]:36801 "EHLO mail-oi0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752257AbbAJPbO (ORCPT ); Sat, 10 Jan 2015 10:31:14 -0500 Received: by mail-oi0-f48.google.com with SMTP id u20so15637164oif.7 for ; Sat, 10 Jan 2015 07:31:13 -0800 (PST) Date: Sat, 10 Jan 2015 08:31:09 -0700 From: Bjorn Helgaas To: Sasha Levin Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Alex Williamson , Konrad Rzeszutek Wilk , Alexander Graf , Greg Kroah-Hartman , "open list:PCI SUBSYSTEM" , Kim Phillips , Stuart Yoder Subject: Re: [PATCH v2] PCI/sysfs: off by two when checking the limit on driver_override length Message-ID: <20150110153109.GJ6575@google.com> References: <1420663977-30707-1-git-send-email-sasha.levin@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1420663977-30707-1-git-send-email-sasha.levin@oracle.com> Sender: linux-pci-owner@vger.kernel.org List-ID: [+cc Kim, Stuart] On Wed, Jan 07, 2015 at 03:52:57PM -0500, Sasha Levin wrote: > When printing the driver_override parameter when it is 4095 and 4094 bytes > long the printing code would access invalid memory because we need count+1 > bytes for printing. Hi Sasha, I swear I'm not trying to be a nuisance, but wasn't there another fix for a different memory corruption problem? I was expecting two patches, but I only see one. If I understand this right, the problem is that driver_override_show() adds "\n" at the end of the driver name, and the whole string (driver name + newline) must fit within a page because sysfs show functions only have a page to put their data in. So the buffer overrun is in driver_override_show(), but the proposed fix is in driver_override_store(). I think that's too complicated. I'd rather use snprintf(..., PAGE_SIZE, ...) in driver_override_show() because that's a common pattern and it's easy to verify that it's correct. I don't think it's worth it to validate the length in driver_override_store(). I think the pattern in resume_store() should be sufficient, e.g., if (count && buf[count - 1] == '\n') count--; name = kstrndup(buf, count, GFP_KERNEL); if (!name) return -ENOMEM; pdev->driver_override = name; kfree(old); If a user sets a driver name that's 4KB long, and the output of driver_override_show() is truncated, that doesn't seem like a real issue. driver_override_store()/driver_override_show() in drivers/base/platform.c (added by 3d713e0e382e ("driver core: platform: add device binding path 'driver_override'")) is basically the same code, and it looks like it has the same two problems. Can you add fix those at the same time? Bjorn > Cc: # v3.16+ > Fixes: 782a985d ("PCI: Introduce new device binding path using pci_dev.driver_override") > Cc: Alex Williamson > Cc: Bjorn Helgaas > Cc: Konrad Rzeszutek Wilk > Cc: Alexander Graf > Cc: Greg Kroah-Hartman > Signed-off-by: Sasha Levin > --- > drivers/pci/pci-sysfs.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > index aa012fb..17459ed 100644 > --- a/drivers/pci/pci-sysfs.c > +++ b/drivers/pci/pci-sysfs.c > @@ -521,7 +521,8 @@ static ssize_t driver_override_store(struct device *dev, > struct pci_dev *pdev = to_pci_dev(dev); > char *driver_override, *old = pdev->driver_override, *cp; > > - if (count > PATH_MAX) > + /* We need to keep extra room for a newline */ > + if (count >= (PATH_MAX - 1)) > return -EINVAL; > > driver_override = kstrndup(buf, count, GFP_KERNEL); > -- > 1.7.10.4 >