[PATCH iproute2] iptunnel: detect protocol mismatch on tunnel change

[PATCH iproute2] iptunnel: detect protocol mismatch on tunnel change

[Stephen Hemminger]

If attempt is made to change an IPv6 tunnel by using IPv4
parameters, a stack overflow would happen and garbage request
would be passed to kernel.

Example:
ip tunnel add gre1 mode ip6gre local 2001:db8::1 remote 2001:db8::2 ttl 255
ip tunnel change gre1 mode gre local 192.168.0.0 remote 192.168.0.1 ttl 255

The second command should fail because it attempting set IPv4 addresses
on a GRE tunnel that is IPv6.

Do best effort detection of this mismatch by giving a bigger buffer to get
tunnel request, and checking that the IP header is IPv4. It is still possible
but unlikely that byte would match in IPv6 tunnel paramater, but good enough
to catch the obvious cases.

Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1032642
Reported-by: Robin <imer@imer.cc>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 ip/iptunnel.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/ip/iptunnel.c b/ip/iptunnel.c
index 02c3670b469d..b6da145913d6 100644
--- a/ip/iptunnel.c
+++ b/ip/iptunnel.c
@@ -17,6 +17,7 @@
 #include <net/if_arp.h>
 #include <linux/ip.h>
 #include <linux/if_tunnel.h>
+#include <linux/ip6_tunnel.h>
 
 #include "rt_names.h"
 #include "utils.h"
@@ -172,11 +173,20 @@ static int parse_args(int argc, char **argv, int cmd, struct ip_tunnel_parm *p)
 			if (get_ifname(p->name, *argv))
 				invarg("\"name\" not a valid ifname", *argv);
 			if (cmd == SIOCCHGTUNNEL && count == 0) {
-				struct ip_tunnel_parm old_p = {};
+				union {
+					struct ip_tunnel_parm ip_tnl;
+					struct ip6_tnl_parm2 ip6_tnl;
+				} old_p = {};
 
 				if (tnl_get_ioctl(*argv, &old_p))
 					return -1;
-				*p = old_p;
+
+				if (old_p.ip_tnl.iph.version != 4 ||
+				    old_p.ip_tnl.iph.ihl != 5)
+					invarg("\"name\" is not an ip tunnel",
+					       *argv);
+
+				*p = old_p.ip_tnl;
 			}
 		}
 		count++;
-- 
2.39.2

Re: [PATCH iproute2] iptunnel: detect protocol mismatch on tunnel change

[Luca Boccassi]

On Tue, 11 Apr 2023 at 00:35, Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> If attempt is made to change an IPv6 tunnel by using IPv4
> parameters, a stack overflow would happen and garbage request
> would be passed to kernel.
>
> Example:
> ip tunnel add gre1 mode ip6gre local 2001:db8::1 remote 2001:db8::2 ttl 255
> ip tunnel change gre1 mode gre local 192.168.0.0 remote 192.168.0.1 ttl 255
>
> The second command should fail because it attempting set IPv4 addresses
> on a GRE tunnel that is IPv6.
>
> Do best effort detection of this mismatch by giving a bigger buffer to get
> tunnel request, and checking that the IP header is IPv4. It is still possible
> but unlikely that byte would match in IPv6 tunnel paramater, but good enough
> to catch the obvious cases.
>
> Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1032642
> Reported-by: Robin <imer@imer.cc>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  ip/iptunnel.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/ip/iptunnel.c b/ip/iptunnel.c
> index 02c3670b469d..b6da145913d6 100644
> --- a/ip/iptunnel.c
> +++ b/ip/iptunnel.c
> @@ -17,6 +17,7 @@
>  #include <net/if_arp.h>
>  #include <linux/ip.h>
>  #include <linux/if_tunnel.h>
> +#include <linux/ip6_tunnel.h>
>
>  #include "rt_names.h"
>  #include "utils.h"
> @@ -172,11 +173,20 @@ static int parse_args(int argc, char **argv, int cmd, struct ip_tunnel_parm *p)
>                         if (get_ifname(p->name, *argv))
>                                 invarg("\"name\" not a valid ifname", *argv);
>                         if (cmd == SIOCCHGTUNNEL && count == 0) {
> -                               struct ip_tunnel_parm old_p = {};
> +                               union {
> +                                       struct ip_tunnel_parm ip_tnl;
> +                                       struct ip6_tnl_parm2 ip6_tnl;
> +                               } old_p = {};
>
>                                 if (tnl_get_ioctl(*argv, &old_p))
>                                         return -1;
> -                               *p = old_p;
> +
> +                               if (old_p.ip_tnl.iph.version != 4 ||
> +                                   old_p.ip_tnl.iph.ihl != 5)
> +                                       invarg("\"name\" is not an ip tunnel",
> +                                              *argv);
> +
> +                               *p = old_p.ip_tnl;
>                         }
>                 }
>                 count++;

Tested-by: Luca Boccassi <bluca@debian.org>

Can confirm it doesn't crash anymore, thanks.

Re: [PATCH iproute2] iptunnel: detect protocol mismatch on tunnel change

[David Ahern]

On 4/10/23 5:35 PM, Stephen Hemminger wrote:
> diff --git a/ip/iptunnel.c b/ip/iptunnel.c
> index 02c3670b469d..b6da145913d6 100644
> --- a/ip/iptunnel.c
> +++ b/ip/iptunnel.c
> @@ -17,6 +17,7 @@
>  #include <net/if_arp.h>
>  #include <linux/ip.h>
>  #include <linux/if_tunnel.h>
> +#include <linux/ip6_tunnel.h>
>  
>  #include "rt_names.h"
>  #include "utils.h"
> @@ -172,11 +173,20 @@ static int parse_args(int argc, char **argv, int cmd, struct ip_tunnel_parm *p)
>  			if (get_ifname(p->name, *argv))
>  				invarg("\"name\" not a valid ifname", *argv);
>  			if (cmd == SIOCCHGTUNNEL && count == 0) {
> -				struct ip_tunnel_parm old_p = {};
> +				union {
> +					struct ip_tunnel_parm ip_tnl;
> +					struct ip6_tnl_parm2 ip6_tnl;
> +				} old_p = {};'

That addresses the stack smashing, but ....

>  
>  				if (tnl_get_ioctl(*argv, &old_p))
>  					return -1;
> -				*p = old_p;
> +
> +				if (old_p.ip_tnl.iph.version != 4 ||
> +				    old_p.ip_tnl.iph.ihl != 5)

this field overlays laddr in ip6_tnl_parm2 which means there is a
collision in valid addresses.


> +					invarg("\"name\" is not an ip tunnel",
> +					       *argv);
> +
> +				*p = old_p.ip_tnl;
>  			}
>  		}
>  		count++;

Re: [PATCH iproute2] iptunnel: detect protocol mismatch on tunnel change

[Stephen Hemminger]

On Tue, 11 Apr 2023 09:55:25 -0600
David Ahern <dsahern@kernel.org> wrote:

> That addresses the stack smashing, but ....
> 
> >  
> >  				if (tnl_get_ioctl(*argv, &old_p))
> >  					return -1;
> > -				*p = old_p;
> > +
> > +				if (old_p.ip_tnl.iph.version != 4 ||
> > +				    old_p.ip_tnl.iph.ihl != 5)  
> 
> this field overlays laddr in ip6_tnl_parm2 which means there is a
> collision in valid addresses.

That is why the commit message said this is best effort.
What happens when there is a collision with a valid address is that
the call will fail later as a bogus change to an IP6 tunnel.

 # ip tunnel add gre1 mode ip6gre local 4545:db8::1 remote 2001:db8::2 ttl 255
 # ip tunnel change gre1 mode gre local 192.168.0.0 remote 192.168.0.1 ttl 255
ttl != 0 and nopmtudisc are incompatible

This is off in the non-standard IPv6 address range so not a likely
to bother anyone.

Re: [PATCH iproute2] iptunnel: detect protocol mismatch on tunnel change

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to iproute2/iproute2.git (main)
by Stephen Hemminger <stephen@networkplumber.org>:

On Mon, 10 Apr 2023 16:35:09 -0700 you wrote:
> If attempt is made to change an IPv6 tunnel by using IPv4
> parameters, a stack overflow would happen and garbage request
> would be passed to kernel.
> 
> Example:
> ip tunnel add gre1 mode ip6gre local 2001:db8::1 remote 2001:db8::2 ttl 255
> ip tunnel change gre1 mode gre local 192.168.0.0 remote 192.168.0.1 ttl 255
> 
> [...]

Here is the summary with links:
  - [iproute2] iptunnel: detect protocol mismatch on tunnel change
    https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/commit/?id=8cc2eac60d5f

You are awesome, thank you!
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