ANDROID: ABI fixup for abi break in struct dst_ops

In commit 92f1655aa2b2 ("net: fix __dst_negative_advice() race") the
struct dst_ops callback negative_advice is callback changes function
parameters.  But as this pointer is part of a structure that is tracked
in the ABI checker, the tool triggers when this is changed.

However, the callback pointer is internal to the networking stack, so
changing the function type is safe, so needing to preserve this is not
required.  To do so, switch the function pointer type back to the old
one so that the checking tools pass, AND then do a hard cast of the
function pointer to the new type when assigning and calling the
function.

Bug: 343727534
Fixes: 92f1655aa2b2 ("net: fix __dst_negative_advice() race")
Change-Id: I48d4ab4bbd29f8edc8fbd7923828b7f78a23e12e
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
diff --git a/include/net/dst_ops.h b/include/net/dst_ops.h
index dd7c0b3..382af5f 100644
--- a/include/net/dst_ops.h
+++ b/include/net/dst_ops.h
@@ -12,6 +12,16 @@
 struct sock;
 struct net;
 
+/* *** ANDROID FIXUP ***
+ * These typedefs are used to help fixup the ABI break caused by commit
+ * 92f1655aa2b2 ("net: fix __dst_negative_advice() race") where the
+ * negative_advice callback changed function signatures.
+ * See b/343727534 for more details.
+ * *** ANDROID FIXUP ***
+ */
+typedef void (*android_dst_ops_negative_advice_new_t)(struct sock *sk, struct dst_entry *);
+typedef struct dst_entry * (*android_dst_ops_negative_advice_old_t)(struct dst_entry *);
+
 struct dst_ops {
 	unsigned short		family;
 	unsigned int		gc_thresh;
@@ -24,7 +34,7 @@
 	void			(*destroy)(struct dst_entry *);
 	void			(*ifdown)(struct dst_entry *,
 					  struct net_device *dev, int how);
-	void			(*negative_advice)(struct sock *sk, struct dst_entry *);
+	struct dst_entry *	(*negative_advice)(struct dst_entry *);
 	void			(*link_failure)(struct sk_buff *);
 	void			(*update_pmtu)(struct dst_entry *dst, struct sock *sk,
 					       struct sk_buff *skb, u32 mtu,
diff --git a/include/net/sock.h b/include/net/sock.h
index 8b173a1..2cbece4 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1955,12 +1955,20 @@
 
 static inline void dst_negative_advice(struct sock *sk)
 {
+	/* *** ANDROID FIXUP ***
+	 * See b/343727534 for more details why this typedef is needed here.
+	 * *** ANDROID FIXUP ***
+	 */
+	android_dst_ops_negative_advice_new_t negative_advice;
+
 	struct dst_entry *dst = __sk_dst_get(sk);
 
 	sk_rethink_txhash(sk);
 
-	if (dst && dst->ops->negative_advice)
-		dst->ops->negative_advice(sk, dst);
+	if (dst && dst->ops->negative_advice) {
+		negative_advice = (android_dst_ops_negative_advice_new_t)dst->ops->negative_advice;
+		negative_advice(sk, dst);
+	}
 }
 
 static inline void
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 63453c2..0cf4c49b 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -165,7 +165,7 @@
 	.mtu =			ipv4_mtu,
 	.cow_metrics =		ipv4_cow_metrics,
 	.destroy =		ipv4_dst_destroy,
-	.negative_advice =	ipv4_negative_advice,
+	.negative_advice =	(android_dst_ops_negative_advice_old_t)ipv4_negative_advice,
 	.link_failure =		ipv4_link_failure,
 	.update_pmtu =		ip_rt_update_pmtu,
 	.redirect =		ip_do_redirect,
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 23cfce6..379b62d 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -250,7 +250,7 @@
 	.cow_metrics		=	dst_cow_metrics_generic,
 	.destroy		=	ip6_dst_destroy,
 	.ifdown			=	ip6_dst_ifdown,
-	.negative_advice	=	ip6_negative_advice,
+	.negative_advice	=	(android_dst_ops_negative_advice_old_t)ip6_negative_advice,
 	.link_failure		=	ip6_link_failure,
 	.update_pmtu		=	ip6_rt_update_pmtu,
 	.redirect		=	rt6_do_redirect,
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index cbf9387..0fe167d 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -3949,7 +3949,7 @@
 		if (likely(dst_ops->mtu == NULL))
 			dst_ops->mtu = xfrm_mtu;
 		if (likely(dst_ops->negative_advice == NULL))
-			dst_ops->negative_advice = xfrm_negative_advice;
+			dst_ops->negative_advice = (android_dst_ops_negative_advice_old_t)xfrm_negative_advice;
 		if (likely(dst_ops->link_failure == NULL))
 			dst_ops->link_failure = xfrm_link_failure;
 		if (likely(dst_ops->neigh_lookup == NULL))