net: sock: move ->sk_shutdown out of bitfields.

->sk_shutdown bits share one bitfield with some other bits in sock struct,
such as ->sk_no_check_[r,t]x, ->sk_userlocks ...
sock_setsockopt() may write to these bits, while holding the socket lock.

In case of AF_UNIX sockets, we change ->sk_shutdown bits while holding only
unix_state_lock(). So concurrent setsockopt() and shutdown() may lead
to corrupting these bits.

Fix this by moving ->sk_shutdown bits out of bitfield into a separate byte.
This will not change the 'struct sock' size since ->sk_shutdown moved into
previously unused 16-bit hole.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Suggested-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -382,8 +382,13 @@ struct sock {
 	atomic_t		sk_omem_alloc;
 	int			sk_sndbuf;
 	struct sk_buff_head	sk_write_queue;
+
+	/*
+	 * Because of non atomicity rules, all
+	 * changes are protected by socket lock.
+	 */
 	kmemcheck_bitfield_begin(flags);
-	unsigned int		sk_shutdown  : 2,
+	unsigned int		sk_padding : 2,
 				sk_no_check_tx : 1,
 				sk_no_check_rx : 1,
 				sk_userlocks : 4,
@@ -391,6 +396,7 @@ struct sock {
 				sk_type      : 16;
 #define SK_PROTOCOL_MAX U8_MAX
 	kmemcheck_bitfield_end(flags);
+
 	int			sk_wmem_queued;
 	gfp_t			sk_allocation;
 	u32			sk_pacing_rate; /* bytes per second */
@@ -418,6 +424,7 @@ struct sock {
 	struct timer_list	sk_timer;
 	ktime_t			sk_stamp;
 	u16			sk_tsflags;
+	u8			sk_shutdown;
 	u32			sk_tskey;
 	struct socket		*sk_socket;
 	void			*sk_user_data;