userns: Convert bsd process accounting to use kuid and kgid where appropriate

BSD process accounting conveniently passes the file the accounting
records will be written into to do_acct_process.  The file credentials
captured the user namespace of the opener of the file.  Use the file
credentials to format the uid and the gid of the current process into
the user namespace of the user that started the bsd process
accounting.

Cc: Pavel Emelyanov <xemul@openvz.org>
Reviewed-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

init/Kconfig

@@ -931,7 +931,6 @@ config UIDGID_CONVERTED
 	depends on FS_POSIX_ACL = n
 	depends on QUOTA = n
 	depends on QUOTACTL = n
-	depends on BSD_PROCESS_ACCT = n
 
 	# Networking
 	depends on NET_9P = n

kernel/acct.c

@@ -507,8 +507,8 @@ static void do_acct_process(struct bsd_acct_struct *acct,
 	do_div(elapsed, AHZ);
 	ac.ac_btime = get_seconds() - elapsed;
 	/* we really need to bite the bullet and change layout */
-	ac.ac_uid = orig_cred->uid;
-	ac.ac_gid = orig_cred->gid;
+	ac.ac_uid = from_kuid_munged(file->f_cred->user_ns, orig_cred->uid);
+	ac.ac_gid = from_kgid_munged(file->f_cred->user_ns, orig_cred->gid);
 #if ACCT_VERSION==2
 	ac.ac_ahz = AHZ;
 #endif