linux-kernel - Re: [PATCH] IPVS: replace sprintf to snprintf to avoid stack buffer overflow

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Date:	Tue, 6 Apr 2010 13:26:42 +1000
From:	Simon Horman <horms@...ge.net.au>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	wzt.wzt@...il.com, linux-kernel@...r.kernel.org,
	wensong@...ux-vs.org, Julian Anastasov <ja@....bg>,
	netdev@...r.kernel.org, lvs-devel@...r.kernel.org,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH] IPVS: replace sprintf to snprintf to avoid stack
 buffer overflow

On Tue, Apr 06, 2010 at 10:58:28AM +0800, Changli Gao wrote:
> On Tue, Apr 6, 2010 at 10:50 AM,  <wzt.wzt@...il.com> wrote:
> > IPVS not check the length of pp->name, use sprintf will cause stack buffer overflow.
> > struct ip_vs_protocol{} declare name as char *, if register a protocol as:
> > struct ip_vs_protocol ip_vs_test = {
> >        .name =                 "aaaaaaaa....128...aaa",
> >        .debug_packet =         ip_vs_tcpudp_debug_packet,
> > };
> >
> > when called ip_vs_tcpudp_debug_packet(), sprintf(buf, "%s TRUNCATED", pp->name);
> > will cause stack buffer overflow.
> >
> 
> Long messages will be truncated instead of buffer overflow. We need to
> find a way to handle long messages elegantly.

Its really a corner case. In practice protocol modules don't have really
long names. And if one was merged that did, the buffer size could be increased
at that time.

So while I think its reasonable to protect against something unexpected
in a protocol-module name crashing the system. Especially as that
can be achieved without any real overhead. I don't think we need
to sanitise the output.
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