linux-hardening - Re: [PATCH] usb: ch9: Replace bmSublinkSpeedAttr 1-element array with flexible array

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Date:   Thu, 6 Jul 2023 08:47:18 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Jó Ágila Bitsch <jgilab@...il.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] usb: ch9: Replace bmSublinkSpeedAttr 1-element array
 with flexible array

On Wed, Jul 05, 2023 at 02:11:03PM -0700, Kees Cook wrote:
> On Thu, Jun 29, 2023 at 09:17:23PM +0200, Greg Kroah-Hartman wrote:
> > On Thu, Jun 29, 2023 at 12:09:00PM -0700, Kees Cook wrote:
> > > Since commit df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3"),
> > > UBSAN_BOUNDS no longer pretends 1-element arrays are unbounded. Walking
> > > bmSublinkSpeedAttr will trigger a warning, so make it a proper flexible
> > > array. Add a union to keep the struct size identical for userspace in
> > > case anything was depending on the old size.
> > > 
> > > False positive warning was:
> > > 
> > > UBSAN: array-index-out-of-bounds in drivers/usb/host/xhci-hub.c:231:31 index 1 is out of range for type '__le32 [1]'
> > > 
> > > for this line of code:
> > > 
> > > 	ssp_cap->bmSublinkSpeedAttr[offset++] = cpu_to_le32(attr);
> > > 
> > > Reported-by: Borislav Petkov <bp@...en8.de>
> > > Closes: https://lore.kernel.org/lkml/2023062945-fencing-pebble-0411@gregkh/
> > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> > > Signed-off-by: Kees Cook <keescook@...omium.org>
> > > ---
> > >  include/uapi/linux/usb/ch9.h | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > Thanks for the quick response, I'll queue it up after 6.5-rc1 is out.
> 
> I'm going to send this before -rc1, since we've had another report[1] that
> was fixed by this. Given the verification there and Boris's testing, I
> think this is good to land. I'll toss it in -next now and send it to
> Linus on Friday after making sure there are no more surprises.
> 
> -Kees
> 
> [1] https://lore.kernel.org/lkml/DA3FEB08-DF39-406B-89CC-9076CFCF597A@kernel.org/

No problem:

Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>