[PATCH] ipv6: Use memset_after() to zero rt6_info

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Use memset_after() to clear everything after the dst_entry member of
struct rt6_info.

Signed-off-by: Kees Cook <redacted>
---
 net/ipv6/route.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 3ae25b8ffbd6..0cf616b2d013 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -328,9 +328,7 @@ static const struct rt6_info ip6_blk_hole_entry_template = {
 
 static void rt6_info_init(struct rt6_info *rt)
 {
-	struct dst_entry *dst = &rt->dst;
-
-	memset(dst + 1, 0, sizeof(*rt) - sizeof(*dst));
+	memset_after(rt, 0, dst);
 	INIT_LIST_HEAD(&rt->rt6i_uncached);
 }
 

-- 
2.30.2

Hello:

This patch was applied to netdev/net-next.git (master)
by David S. Miller [off-list ref]:

On Thu, 18 Nov 2021 12:32:41 -0800 you wrote:

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Use memset_after() to clear everything after the dst_entry member of
struct rt6_info.

[...]

Here is the summary with links:
  - ipv6: Use memset_after() to zero rt6_info
    https://git.kernel.org/netdev/net-next/c/8f2a83b454c9

You are awesome, thank you!
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