Re: [PATCH] usb: gadget: aspeed: fix buffer overflow

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Lei Yu <yulei.sh@bytedance.com>
Cc: Felipe Balbi <balbi@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Joel Stanley <joel@jms.id.au>, Andrew Jeffery <andrew@aj.id.au>,
	Henry Tian <tianxiaofeng@bytedance.com>,
	Jakob Koschel <jakobkoschel@gmail.com>,
	linux-usb@vger.kernel.org,
	"moderated list:ARM/ASPEED MACHINE SUPPORT"
	<linux-arm-kernel@lists.infradead.org>,
	"moderated list:ARM/ASPEED MACHINE SUPPORT"
	<linux-aspeed@lists.ozlabs.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] usb: gadget: aspeed: fix buffer overflow
Date: Wed, 26 Oct 2022 09:29:23 +1100	[thread overview]
Message-ID: <49d97f97e63edb70392279845186547d73b2290e.camel@kernel.crashing.org> (raw)
In-Reply-To: <CAGm54UE1oS1N_hn4RKuF8a+OWgfvJ-OCc0-uju4mXbtz-jw8VA@mail.gmail.com>

On Tue, 2022-10-25 at 14:21 +0800, Lei Yu wrote:
> 

> This case is treated as an error and we do not care about the
> following data.
> Similarly, if we change the MTU in BMC and let BMC ping the OS, the
> OS
> kernel does not crash and it gets RX errors, and the ping fails.
> 
>  # ifconfig usb0
>  usb0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
>          ...
>          RX packets 85  bytes 15380 (15.0 KiB)
>          RX errors 51  dropped 0  overruns 0  frame 51
> 
> With this patch, we get the similar behavior on BMC that the RX
> errors
> are increasing.
> 
> > Additionally, I'm curious, why in this specific case is the device
> > sending more data than
> > the buffer can hold ? The MTU change should have resulted in
> > buffers being re-allocated no ?
> 
> The issue is found in a rare case during BIOS boot, we assume that
> BIOS is sending unexpected data to BMC for unknown reasons.

Ok thanks.

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

> > Or did you change the MTU on the remote and not on the local device
> > ?
> > 
> 
> Yes, the MTU is changed to 2000 in OS and kept 1500 on BMC, then the
> issue is reproduced. (see detailed steps in the above email).
> 
> The reason we made the above test is because we are trying to
> reproduce the behavior as BIOS, and from the logs it looks like it's
> sending a packet larger than MTU. Then we tried to adjust the MTU on
> the OS side and reproduced the issue.

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