ipv4/inet_sock.h: Avoid thousands of -Wflex-array-member-not-at-end warnings

Use DEFINE_RAW_FLEX() to avoid thousands of -Wflex-array-member-not-at-end
warnings.

Remove struct ip_options_data, and adjust the rest of the code so that
flexible-array member struct ip_options_rcu::opt.__data[] ends last
in struct icmp_bxm.

Compensate for this by using the DEFINE_RAW_FLEX() helper to define each
on-stack struct instance that contained struct ip_options_data as a member,
and to define struct ip_options_rcu with a fixed on-stack size for its
nested flexible-array member opt.__data[].

Also, add a couple of code comments to prevent people from adding members
to a struct after another member that contains a flexible array.

With these changes, fix 2600 warnings of the following type:

include/net/inet_sock.h:65:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://patch.msgid.link/aVteBadWA6AbTp7X@kspp
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 5998c4cc6f47..e20c41206e29 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -481,6 +481,8 @@ static int raw_getfrag(void *from, char *to, int offset, int len, int odd,
 
 static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 {
+	DEFINE_RAW_FLEX(struct ip_options_rcu, opt_copy, opt.__data,
+			IP_OPTIONS_DATA_FIXED_SIZE);
 	struct inet_sock *inet = inet_sk(sk);
 	struct net *net = sock_net(sk);
 	struct ipcm_cookie ipc;
@@ -491,7 +493,6 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	__be32 daddr;
 	__be32 saddr;
 	int uc_index, err;
-	struct ip_options_data opt_copy;
 	struct raw_frag_vec rfv;
 	int hdrincl;
 
@@ -561,9 +562,9 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		rcu_read_lock();
 		inet_opt = rcu_dereference(inet->inet_opt);
 		if (inet_opt) {
-			memcpy(&opt_copy, inet_opt,
+			memcpy(opt_copy, inet_opt,
 			       sizeof(*inet_opt) + inet_opt->opt.optlen);
-			ipc.opt = &opt_copy.opt;
+			ipc.opt = opt_copy;
 		}
 		rcu_read_unlock();
 	}