Messages in this thread | | | Subject | Re: [PATCH] USB: core: limit access to rawdescriptors which were not allocated | From | "Xu, Yanfei" <> | Date | Wed, 26 Aug 2020 14:56:49 +0800 |
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On 8/26/20 2:00 AM, Alan Stern wrote: > On Wed, Aug 26, 2020 at 12:16:59AM +0800, yanfei.xu@windriver.com wrote: >> From: Yanfei Xu <yanfei.xu@windriver.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@syzkaller.appspotmail.com >> Signed-off-by: Yanfei Xu <yanfei.xu@windriver.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. Thanks for you suggestion. The patch is not right. I'll try to look into the root cause.
Regard, Yanfei. > > Alan Stern >
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