Re: [PATCH v2] usb: fix various gadget panics on 10gbps cabling

From: Felipe Balbi <balbi@kernel.org>
To: "Maciej Żenczykowski" <zenczykowski@gmail.com>,
	"Maciej Żenczykowski" <maze@google.com>
Cc: Linux USB Mailing List <linux-usb@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v2] usb: fix various gadget panics on 10gbps cabling
Date: Thu, 10 Jun 2021 12:10:07 +0300	[thread overview]
Message-ID: <878s3i2ihc.fsf@kernel.org> (raw)
In-Reply-To: <20210609024459.1126080-1-zenczykowski@gmail.com>

[-- Attachment #1: Type: text/plain, Size: 1835 bytes --]

Maciej Żenczykowski <zenczykowski@gmail.com> writes:

> From: Maciej Żenczykowski <maze@google.com>
>
> usb_assign_descriptors() is called with 5 parameters,
> the last 4 of which are the usb_descriptor_header for:
>   full-speed (USB1.1 - 12Mbps [including USB1.0 low-speed @ 1.5Mbps),
>   high-speed (USB2.0 - 480Mbps),
>   super-speed (USB3.0 - 5Gbps),
>   super-speed-plus (USB3.1 - 10Gbps).
>
> The differences between full/high/super-speed descriptors are usually
> substantial (due to changes in the maximum usb block size from 64 to 512
> to 1024 bytes and other differences in the specs), while the difference
> between 5 and 10Gbps descriptors may be as little as nothing
> (in many cases the same tuning is simply good enough).
>
> However if a gadget driver calls usb_assign_descriptors() with
> a NULL descriptor for super-speed-plus and is then used on a max 10gbps
> configuration, the kernel will crash with a null pointer dereference,
> when a 10gbps capable device port + cable + host port combination shows up.
> (This wouldn't happen if the gadget max-speed was set to 5gbps, but
> it of course defaults to the maximum, and there's no real reason to
> artificially limit it)
>
> The fix is to simply use the 5gbps descriptor as the 10gbps descriptor,
> if a 10gbps descriptor wasn't provided.
>
> Obviously this won't fix the problem if the 5gbps descriptor is also
> NULL, but such cases can't be so trivially solved (and any such gadgets
> are unlikely to be used with USB3 ports any way).
>
> Cc: Felipe Balbi <balbi@kernel.org>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Maciej Żenczykowski <maze@google.com>

nice catch!!

I think this is already in Greg's tree, but in any  case:

Acked-by: Felipe Balbi <balbi@kernel.org>

-- 
balbi

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 511 bytes --]