On Tue, Jun 13, 2023 at 01:46:54PM -0700, Kees Cook wrote:
> On Sun, Jun 11, 2023 at 09:41:30PM +0800, kernel test robot wrote:
> > the issue we found below is by clang-15, but we confirmed clang-15 we use is
> > commit 8dfdcc7b7b in llvm-project. it supports the flag already.
>
> Interesting! Thanks for the report.
>
> > [ 228.605608][ C1] BUG: unable to handle page fault for address: 04090300
> > [...]
> > [ 228.608262][ C1] EIP: string (lib/vsprintf.c:644 lib/vsprintf.c:726)
> > [...]
> > [ 228.608262][ C1] Call Trace:
> > [ 228.608262][ C1] <SOFTIRQ>
> > [ 228.608262][ C1] vsnprintf (lib/vsprintf.c:2817)
> > [ 228.608262][ C1] vprintk_store (kernel/printk/printk.c:2191)
> > [ 228.608262][ C1] vprintk_emit (kernel/printk/printk.c:2288)
> > [ 228.608262][ C1] vprintk_default (kernel/printk/printk.c:2318)
> > [ 228.608262][ C1] vprintk (kernel/printk/printk_safe.c:50)
> > [ 228.608262][ C1] _printk (kernel/printk/printk.c:2331)
> > [ 228.608262][ C1] __ubsan_handle_out_of_bounds (lib/ubsan.c:209 lib/ubsan.c:343)
>
> This is a crash within the UBSAN handler! That's very unexpected.
I still don't understand this. Is printk() not allowed in SOFTIRQ?
> > [ 228.608262][ C1] get_string (drivers/usb/gadget/composite.c:1314)
> > [ 228.608262][ C1] composite_setup (drivers/usb/gadget/composite.c:1871)
> > [ 228.608262][ C1] dummy_timer (drivers/usb/gadget/udc/dummy_hcd.c:?)
>
> And the out-of-bounds condition got triggered in dummy_hcd.
I found this. I'm surprised we didn't trip over it earlier!
/* USB_DT_STRING: String descriptor */
struct usb_string_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__le16 wData[1]; /* UTF-16LE encoded */
} __attribute__ ((packed));
$ git grep 'struct usb_string_descriptor'
drivers/usb/early/xhci-dbc.c: struct usb_string_descriptor *s_desc;
drivers/usb/early/xhci-dbc.c: s_desc = (struct usb_string_descriptor *)strings->serial;
drivers/usb/early/xhci-dbc.c: s_desc = (struct usb_string_descriptor *)strings->product;
drivers/usb/early/xhci-dbc.c: s_desc = (struct usb_string_descriptor *)strings->manufacturer;
drivers/usb/gadget/composite.c: struct usb_string_descriptor *s = buf;
drivers/usb/gadget/udc/aspeed-vhub/hub.c: struct usb_string_descriptor *sdesc = buf;
drivers/usb/host/xhci-dbgcap.c: struct usb_string_descriptor *s_desc;
drivers/usb/host/xhci-dbgcap.c: s_desc = (struct usb_string_descriptor *)strings->serial;
drivers/usb/host/xhci-dbgcap.c: s_desc = (struct usb_string_descriptor *)strings->product;
drivers/usb/host/xhci-dbgcap.c: s_desc = (struct usb_string_descriptor *)strings->manufacturer;
include/uapi/linux/usb/ch9.h:struct usb_string_descriptor {
Looking at each use, none are using sizeof() on the struct, so it should
be a trivial replacement. I'll send a patch.
-Kees
--
Kees Cook
