[PATCH 4/5] sulogin: mount temporary /dev and /proc if not found

[Werner Fink <werner@xxxxxxx>]

This is very usefull if initrd can not loaded that is no /dev and no
/proc is found.  Also if the /etc/shadow and /etc/passwd is copied into
the initrd the sulogin can be used in initrd even before /dev and/or /proc
are mounted.

Signed-off-by: Werner Fink <werner@xxxxxxx>
---
 configure.ac          |   10 ++++++++
 login-utils/sulogin.c |   57 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)

diff --git configure.ac configure.ac
index 3be3715..631002f 100644
--- configure.ac
+++ configure.ac
@@ -1296,6 +1296,16 @@ if test "x$enable_use_tty_group" = xyes; then
   AC_DEFINE(USE_TTY_GROUP, 1, [Should wall and write be installed setgid tty?])
 fi
 
+AC_ARG_ENABLE([use-emergency-dev],
+  AS_HELP_STRING([--disable-use-emergency-dev], [do not use emergency mount of /dev and /proc for sulogin]),
+  [], enable_use_emergency_dev=yes
+)
+AM_CONDITIONAL(USE_EMERGENCY_DEV, test "x$enable_use_emergency_dev" = xyes)
+
+if test "x$enable_use_emergency_dev" = xyes; then
+  AC_DEFINE(USE_EMERGENCY_DEV, 1, [Should sulogin use a emergency mount of /dev and /proc?])
+fi
+
 AC_ARG_ENABLE([makeinstall-chown],
   AS_HELP_STRING([--disable-makeinstall-chown], [do not do chown-like operations during "make install"]),
   [], enable_makeinstall_chown=yes
diff --git login-utils/sulogin.c login-utils/sulogin.c
index dbcc855..0b0d21c 100644
--- login-utils/sulogin.c
+++ login-utils/sulogin.c
@@ -47,6 +47,20 @@
 # include <selinux/get_context_list.h>
 #endif
 
+#ifdef USE_EMERGENCY_DEV
+# include <sys/statfs.h>
+# include <sys/mount.h>
+# include <linux/fs.h>
+# include <linux/magic.h>
+# include <linux/major.h>
+# ifndef TMPFS_MAGIC
+#  define TMPFS_MAGIC	0x01021994
+# endif
+# ifndef MNT_DETACH
+#  define MNT_DETACH	2
+# endif
+#endif
+
 #include "c.h"
 #include "closestream.h"
 #include "nls.h"
@@ -441,6 +455,49 @@ static void fixtty(void)
 		warn(_("tcsetattr failed"));
 }
 
+#ifdef USE_EMERGENCY_DEV
+/*
+ * Make C library standard calls such like ttyname(3) work
+ * even if the system does not show any of the standard
+ * directories.
+ */
+
+static uint32_t mounts;
+# define MNT_PROCFS	0x0001
+# define MNT_DEVTMPFS	0x0002
+
+static __attribute__((__noinline__)) void putmounts(void)
+{
+	if (mounts & MNT_DEVTMPFS)
+		umount2("/dev", MNT_DETACH);
+	if (mounts & MNT_PROCFS)
+		umount2("/proc", MNT_DETACH);
+}
+
+# define dovoid(f)	if ((f)){}
+static __attribute__((__constructor__)) void getmounts(void)
+{
+	struct statfs st;
+	if (statfs("/proc", &st) == 0 && st.f_type != PROC_SUPER_MAGIC) {
+		if (mount("proc", "/proc", "proc", MS_RELATIME, NULL) == 0)
+			mounts |= MNT_PROCFS;
+	}
+	if (statfs("/dev", &st) == 0 && st.f_type != TMPFS_MAGIC) {
+		if (mount("devtmpfs", "/dev", "devtmpfs", MS_RELATIME, "mode=0755,nr_inodes=0") == 0) {
+			mounts |= MNT_DEVTMPFS;
+			(void)mknod("/dev/console", S_IFCHR|S_IRUSR|S_IWUSR, makedev(TTYAUX_MAJOR, 1));
+			if (symlink("/proc/self/fd", "/dev/fd") == 0) {
+				dovoid(symlink("fd/0", "/dev/stdin"));
+				dovoid(symlink("fd/1", "/dev/stdout"));
+				dovoid(symlink("fd/2", "/dev/stderr"));
+			}
+		}
+	}
+	if (mounts) atexit(putmounts);
+}
+# undef dovoid
+#endif
+
 static void usage(FILE *out)
 {
 	fputs(USAGE_HEADER, out);
-- 
1.7.10.4

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