Date: Tue, 17 Dec 2002 09:37:34 -0800 From: "Sam Leffler" <sam@errno.com> To: "Vincent Jardin" <vjardin@wanadoo.fr>, <freebsd-net@FreeBSD.ORG> Subject: Re: Recursive encapsulation could panic the Kernel Message-ID: <050301c2a5f2$fc52aae0$52557f42@errno.com> References: <3DF62DBD0032C2ED@mel-rta6.wanadoo.fr> (added by postmaster@wanadoo.fr)
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> With FreeBSD, there are many ways to create a recursive local encapsulation > loop within the IPv4 and IPv6 stack. For example, this problem shows up when : > - Netgraph with pptp is used or Netgraph with an ng_iface over UDP or any > more complex Netgraph topologies... > - gre interfaces > - gif tunnels > - ... > > There is a simple local solution that is used by gif_output() that is not > protected by any mutex: > /* > * gif may cause infinite recursion calls when misconfigured. > * We'll prevent this by introducing upper limit. > * XXX: this mechanism may introduce another problem about > * mutual exclusion of the variable CALLED, especially if we > * use kernel thread. > */ > if (++called > max_gif_nesting) { > log(LOG_NOTICE, > "gif_output: recursively called too many times(%d)\n", > called); > m_freem(m); > error = EIO; /* is there better errno? */ > goto end; > } > > I am wondering if a more generic solution could be found, however I do not > have any idea yet ;-( > I mean, is it possible to protect the kernel against any panic that could > come from a mis-configuration of the routing tables ? In -current mbufs can be tagged (see m_tag* in sys/mbuf.h); this'll let you do what you want. I've been slow to MFC them to -stable because there are some issues with copying packet headers that I want to resolve first. Sam To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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