[PATCH 38/64] xfrm: Use memset_after() to clear padding

Kees Cook
2021-07-27T21:07:41Z

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

Clear trailing padding bytes using the new helper so that memset()
doesn't get confused about writing "past the end" of the last struct
member. There is no change to the resulting machine code.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
net/xfrm/xfrm_policy.c | 4 +---
net/xfrm/xfrm_user.c | 2 +-
2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 37d17a79617c..1a06585022ab 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2486,9 +2486,7 @@ static inline struct xfrm_dst *xfrm_alloc_dst(struct net *net, int family)
xdst = dst_alloc(dst_ops, NULL, 1, DST_OBSOLETE_NONE, 0);

if (likely(xdst)) {
- struct dst_entry *dst = &xdst->u.dst;
-
- memset(dst + 1, 0, sizeof(*xdst) - sizeof(*dst));
+ memset_after(xdst, 0, u.dst);
} else
xdst = ERR_PTR(-ENOBUFS);

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index acc3a0dab331..0bf8fec3fd97 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2907,7 +2907,7 @@ static int build_expire(struct sk_buff *skb, struct xfrm_state *x, const struct
copy_to_user_state(x, &ue->state);
ue->hard = (c->data.hard != 0) ? 1 : 0;
/* clear the padding bytes */
- memset(&ue->hard + 1, 0, sizeof(*ue) - offsetofend(typeof(*ue), hard));
+ memset_after(ue, 0, hard);

err = xfrm_mark_put(skb, &x->mark);
if (err)
--
2.30.2