Patch "ipv6 sit: work around bogus gcc-8 -Wrestrict warning" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

ipv6 sit: work around bogus gcc-8 -Wrestrict warning

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ipv6-sit-work-around-bogus-gcc-8-wrestrict-warning.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Arnd Bergmann <[email protected]>
Date: Thu, 22 Feb 2018 16:55:34 +0100
Subject: ipv6 sit: work around bogus gcc-8 -Wrestrict warning

From: Arnd Bergmann <[email protected]>

[ Upstream commit ca79bec237f5809a7c3c59bd41cd0880aa889966 ]

gcc-8 has a new warning that detects overlapping input and output arguments in memcpy(). It triggers for sit_init_net() calling ipip6_tunnel_clone_6rd(), which is actually correct:

net/ipv6/sit.c: In function 'sit_init_net':
net/ipv6/sit.c:192:3: error: 'memcpy' source argument is the same as destination [-Werror=restrict]

The problem here is that the logic detecting the memcpy() arguments finds them to be the same, but the conditional that tests for the input and output of ipip6_tunnel_clone_6rd() to be identical is not a compile-time constant.

We know that netdev_priv(t->dev) is the same as t for a tunnel device, and comparing "dev" directly here lets the compiler figure out as well that 'dev == sitn->fb_tunnel_dev' when called from sit_init_net(), so it no longer warns.

This code is old, so Cc stable to make sure that we don't get the warning for older kernels built with new gcc.

---
 net/ipv6/sit.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -176,7 +176,7 @@ static void ipip6_tunnel_clone_6rd(struc
 #ifdef CONFIG_IPV6_SIT_6RD
 	struct ip_tunnel *t = netdev_priv(dev);
 
-	if (t->dev == sitn->fb_tunnel_dev) {
+	if (dev == sitn->fb_tunnel_dev) {
 		ipv6_addr_set(&t->ip6rd.prefix, htonl(0x20020000), 0, 0, 0);
 		t->ip6rd.relay_prefix = 0;
 		t->ip6rd.prefixlen = 16;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/tpm-constify-transmit-data-pointers.patch queue-4.9/ipv6-sit-work-around-bogus-gcc-8-wrestrict-warning.patch queue-4.9/arm-kvm-fix-building-with-gcc-8.patch