bpf: Convert bpf_sock_addr_kern "uaddr" to sockaddr_unspec

Change struct bpf_sock_addr_kern to use sockaddr_unspec for the "uaddr"
field instead of sockaddr. This improves type safety in the BPF cgroup
socket address filtering code.

The casting in __cgroup_bpf_run_filter_sock_addr() is updated to match the
new type, removing an unnecessary cast in the initialization and updating
the conditional assignment to use the appropriate sockaddr_unspec cast.

Signed-off-by: Kees Cook <[email protected]>

Author: kees

include/linux/filter.h

@@ -1515,7 +1515,7 @@ static inline int bpf_tell_extensions(void)
 
 struct bpf_sock_addr_kern {
 	struct sock *sk;
-	struct sockaddr *uaddr;
+	struct sockaddr_unspec *uaddr;
 	/* Temporary "register" to make indirect stores to nested structures
 	 * defined above. We need three registers to make such a store, but
 	 * only two (src and dst) are available at convert_ctx_access time

kernel/bpf/cgroup.c

@@ -1673,10 +1673,10 @@ int __cgroup_bpf_run_filter_sock_addr(struct sock *sk,
 {
 	struct bpf_sock_addr_kern ctx = {
 		.sk = sk,
-		.uaddr = (struct sockaddr *)uaddr,
+		.uaddr = uaddr,
 		.t_ctx = t_ctx,
 	};
-	struct sockaddr_storage unspec;
+	struct sockaddr_storage storage;
 	struct cgroup *cgrp;
 	int ret;
 
@@ -1688,8 +1688,8 @@ int __cgroup_bpf_run_filter_sock_addr(struct sock *sk,
 		return 0;
 
 	if (!ctx.uaddr) {
-		memset(&unspec, 0, sizeof(unspec));
-		ctx.uaddr = (struct sockaddr *)&unspec;
+		memset(&storage, 0, sizeof(storage));
+		ctx.uaddr = (struct sockaddr_unspec *)&storage;
 		ctx.uaddrlen = 0;
 	} else {
 		ctx.uaddrlen = *uaddrlen;