af_unix: Move SOCK_PASS{CRED,PIDFD,SEC} to struct sock.

As explained in the next patch, SO_PASSRIGHTS would have a problem
if we assigned a corresponding bit to socket->flags, so it must be
managed in struct sock.

Mixing socket->flags and sk->sk_flags for similar options will look
confusing, and sk->sk_flags does not have enough space on 32bit system.

Also, as mentioned in commit 16e572626961 ("af_unix: dont send
SCM_CREDENTIALS by default"), SOCK_PASSCRED and SOCK_PASSPID handling
is known to be slow, and managing the flags in struct socket cannot
avoid that for embryo sockets.

Let's move SOCK_PASS{CRED,PIDFD,SEC} to struct sock.

While at it, other SOCK_XXX flags in net.h are grouped as enum.

Note that assign_bit() was atomic, so the writer side is moved down
after lock_sock() in setsockopt(), but the bit is only read once
in sendmsg() and recvmsg(), so lock_sock() is not needed there.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 22 insertions, 9 deletions

diff --git a/include/linux/net.h b/include/linux/net.h
index 0ff950eecc6b..f8418d6e33e0 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -36,14 +36,13 @@ struct net;
  * in sock->flags, but moved into sk->sk_wq->flags to be RCU protected.
  * Eventually all flags will be in sk->sk_wq->flags.
  */
-#define SOCKWQ_ASYNC_NOSPACE	0
-#define SOCKWQ_ASYNC_WAITDATA	1
-#define SOCK_NOSPACE		2
-#define SOCK_PASSCRED		3
-#define SOCK_PASSSEC		4
-#define SOCK_SUPPORT_ZC		5
-#define SOCK_CUSTOM_SOCKOPT	6
-#define SOCK_PASSPIDFD		7
+enum socket_flags {
+	SOCKWQ_ASYNC_NOSPACE,
+	SOCKWQ_ASYNC_WAITDATA,
+	SOCK_NOSPACE,
+	SOCK_SUPPORT_ZC,
+	SOCK_CUSTOM_SOCKOPT,
+};
 
 #ifndef ARCH_HAS_SOCKET_TYPES
 /**
diff --git a/include/net/sock.h b/include/net/sock.h
index 483522377955..d90a71f66ab8 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -337,6 +337,11 @@ struct sk_filter;
   *	@sk_txtime_deadline_mode: set deadline mode for SO_TXTIME
   *	@sk_txtime_report_errors: set report errors mode for SO_TXTIME
   *	@sk_txtime_unused: unused txtime flags
+  *	@sk_scm_recv_flags: all flags used by scm_recv()
+  *	@sk_scm_credentials: flagged by SO_PASSCRED to recv SCM_CREDENTIALS
+  *	@sk_scm_security: flagged by SO_PASSSEC to recv SCM_SECURITY
+  *	@sk_scm_pidfd: flagged by SO_PASSPIDFD to recv SCM_PIDFD
+  *	@sk_scm_unused: unused flags for scm_recv()
   *	@ns_tracker: tracker for netns reference
   *	@sk_user_frags: xarray of pages the user is holding a reference on.
   *	@sk_owner: reference to the real owner of the socket that calls
@@ -523,7 +528,16 @@ struct sock {
 #endif
 	int			sk_disconnects;
 
-	u8			sk_txrehash;
+	union {
+		u8		sk_txrehash;
+		u8		sk_scm_recv_flags;
+		struct {
+			u8	sk_scm_credentials : 1,
+				sk_scm_security : 1,
+				sk_scm_pidfd : 1,
+				sk_scm_unused : 5;
+		};
+	};
 	u8			sk_clockid;
 	u8			sk_txtime_deadline_mode : 1,
 				sk_txtime_report_errors : 1,