Add backend support for suboridnate uids and gids

These files list the set of subordinate uids and gids that users are allowed
to use.   The expect use case is with the user namespace but other uses are
allowed.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

etc/login.defs

@@ -226,6 +226,10 @@ UID_MAX			60000
 # System accounts
 SYS_UID_MIN		  101
 SYS_UID_MAX		  999
+# Extra per user uids
+SUB_UID_MIN		   100000
+SUB_UID_MAX		600100000
+SUB_UID_COUNT		    10000
 
 #
 # Min/max values for automatic gid selection in groupadd(8)
@@ -235,6 +239,10 @@ GID_MAX			60000
 # System accounts
 SYS_GID_MIN		  101
 SYS_GID_MAX		  999
+# Extra per user group ids
+SUB_GID_MIN		   100000
+SUB_GID_MAX		600100000
+SUB_GID_COUNT		    10000
 
 #
 # Max number of login(1) retries if password is bad

lib/Makefile.am

@@ -39,6 +39,8 @@ libshadow_la_SOURCES = \
 	pwio.c \
 	pwio.h \
 	pwmem.c \
+	subordinateio.h \
+	subordinateio.c \
 	selinux.c \
 	semanage.c \
 	sgetgrent.c \

lib/getdef.c

@@ -81,6 +81,12 @@ static struct itemdef def_table[] = {
 	{"SHA_CRYPT_MAX_ROUNDS", NULL},
 	{"SHA_CRYPT_MIN_ROUNDS", NULL},
 #endif
+	{"SUB_GID_COUNT", NULL},
+	{"SUB_GID_MAX", NULL},
+	{"SUB_GID_MIN", NULL},
+	{"SUB_UID_COUNT", NULL},
+	{"SUB_UID_MAX", NULL},
+	{"SUB_UID_MIN", NULL},
 	{"SULOG_FILE", NULL},
 	{"SU_NAME", NULL},
 	{"SYS_GID_MAX", NULL},