Error with wg-quick down when IPv6 not present

[Jason A. Donenfeld]

On Wed, Sep 25, 2019 at 11:06:18AM +1000, Brassy Panache wrote:
> I have a kernel without IPv6 support.  I've noticed when running:
> 
> $ wg-quick down vpn
> 
> 
> I receive the following errors:
> 
> [#] ip -4 rule delete table 51820
> [#] ip -4 rule delete table main suppress_prefixlength 0
> RTNETLINK answers: Address family not supported by protocol
> Dump terminated
> RTNETLINK answers: Address family not supported by protocol
> Dump terminated
> [#] ip link delete dev vpn
> [#] resolvconf -d vpn -f
> 
> 
> This is caused by the assumption that the command:
> 
> $ ip -6 rule show
> 
> 
> will run on the system.  I have made a change to my local wg-quick script
> which first tests if the command runs successfully before it clears the
> rules.  The same should probably also be done prior to running the IPv4
> version of the command.

Would this work?

diff --git a/src/tools/wg-quick/linux.bash b/src/tools/wg-quick/linux.bash
index e690944d..612ecd77 100755
--- a/src/tools/wg-quick/linux.bash
+++ b/src/tools/wg-quick/linux.bash
@@ -102,10 +102,10 @@ del_if() {
 		while [[ $(ip -4 rule show) == *"from all lookup main suppress_prefixlength 0"* ]]; do
 			cmd ip -4 rule delete table main suppress_prefixlength 0
 		done
-		while [[ $(ip -6 rule show) == *"lookup $table"* ]]; do
+		while [[ $(ip -6 rule show 2>/dev/null) == *"lookup $table"* ]]; do
 			cmd ip -6 rule delete table $table
 		done
-		while [[ $(ip -6 rule show) == *"from all lookup main suppress_prefixlength 0"* ]]; do
+		while [[ $(ip -6 rule show 2>/dev/null) == *"from all lookup main suppress_prefixlength 0"* ]]; do
 			cmd ip -6 rule delete table main suppress_prefixlength 0
 		done
 	fi