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Date: Tue, 25 Aug 2020 14:00:26 -0400 From: Alan Stern <stern@...land.harvard.edu> To: yanfei.xu@...driver.com Cc: gregkh@...uxfoundation.org, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] USB: core: limit access to rawdescriptors which were not allocated On Wed, Aug 26, 2020 at 12:16:59AM +0800, yanfei.xu@...driver.com wrote: > From: Yanfei Xu <yanfei.xu@...driver.com> > > When using systemcall to read the rawdescriptors, make sure we won't > access to the rawdescriptors never allocated, which are number > exceed the USB_MAXCONFIG. > > Reported-by: syzbot+256e56ddde8b8957eabd@...kaller.appspotmail.com > Signed-off-by: Yanfei Xu <yanfei.xu@...driver.com> > --- > drivers/usb/core/sysfs.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c > index a2ca38e25e0c..1a7a625e5f55 100644 > --- a/drivers/usb/core/sysfs.c > +++ b/drivers/usb/core/sysfs.c > @@ -895,7 +895,8 @@ read_descriptors(struct file *filp, struct kobject *kobj, > * configurations (config plus subsidiary descriptors). > */ > for (cfgno = -1; cfgno < udev->descriptor.bNumConfigurations && > - nleft > 0; ++cfgno) { > + nleft > 0 && > + cfgno < USB_MAXCONFIG; ++cfgno) { > if (cfgno < 0) { > src = &udev->descriptor; > srclen = sizeof(struct usb_device_descriptor); This is not the right way to fix the problem. Instead, we should make sure that udev->descriptor.bNumConfigurations is always <= USB_MAXCONFIG. That's what this code in usb_get_configuration() is supposed to do: int ncfg = dev->descriptor.bNumConfigurations; ... if (ncfg > USB_MAXCONFIG) { dev_warn(ddev, "too many configurations: %d, " "using maximum allowed: %d\n", ncfg, USB_MAXCONFIG); dev->descriptor.bNumConfigurations = ncfg = USB_MAXCONFIG; } If you want to fix the bug, you need to figure out why this isn't working. Alan Stern
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