ipv6: remove hard coded limitation on ipv6_pinfo

IPv6 inet sockets are supposed to have a "struct ipv6_pinfo"
field at the end of their definition, so that inet6_sk_generic()
can derive from socket size the offset of the "struct ipv6_pinfo".

This is very fragile, and prevents adding bigger alignment
in sockets, because inet6_sk_generic() does not work
if the compiler adds padding after the ipv6_pinfo component.

We are currently working on a patch series to reorganize
TCP structures for better data locality and found issues
similar to the one fixed in commit f5d547676ca0
("tcp: fix tcp_inet6_sk() for 32bit kernels")

Alternative would be to force an alignment on "struct ipv6_pinfo",
greater or equal to __alignof__(any ipv6 sock) to ensure there is
no padding. This does not look great.

v2: fix typo in mptcp_proto_v6_init() (Paolo)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Chao Wu <wwchao@google.com>
Cc: Wei Wang <weiwan@google.com>
Cc: Coco Li <lixiaoyan@google.com>
Cc: YiFei Zhu <zhuyifei@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 11 deletions

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index ed3d110c2eb5..0295b47c10a3 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -200,14 +200,7 @@ struct inet6_cork {
 	u8 tclass;
 };
 
-/**
- * struct ipv6_pinfo - ipv6 private area
- *
- * In the struct sock hierarchy (tcp6_sock, upd6_sock, etc)
- * this _must_ be the last member, so that inet6_sk_generic
- * is able to calculate its offset from the base struct sock
- * by using the struct proto->slab_obj_size member. -acme
- */
+/* struct ipv6_pinfo - ipv6 private area */
 struct ipv6_pinfo {
 	struct in6_addr 	saddr;
 	struct in6_pktinfo	sticky_pktinfo;
@@ -307,19 +300,19 @@ struct raw6_sock {
 	__u32			offset;		/* checksum offset  */
 	struct icmp6_filter	filter;
 	__u32			ip6mr_table;
-	/* ipv6_pinfo has to be the last member of raw6_sock, see inet6_sk_generic */
+
 	struct ipv6_pinfo	inet6;
 };
 
 struct udp6_sock {
 	struct udp_sock	  udp;
-	/* ipv6_pinfo has to be the last member of udp6_sock, see inet6_sk_generic */
+
 	struct ipv6_pinfo inet6;
 };
 
 struct tcp6_sock {
 	struct tcp_sock	  tcp;
-	/* ipv6_pinfo has to be the last member of tcp6_sock, see inet6_sk_generic */
+
 	struct ipv6_pinfo inet6;
 };