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

Werner Fink
2012-12-10T12:39:42Z

On Fri, Dec 07, 2012 at 12:01:18PM -0500, Dave Reisner wrote:
>
> If you're in the initramfs, rootfs is tmpfs. Won't your statfs check
> return a buffer which has f_type == TMPFS_MAGIC even if /dev is not
> mounted?

Indeed it could be a poroblem, therefore I've moved the stuff to lib/conosle.c
and switch over to device comparission as you suggested. Also if /dev has
been mounted by this code I'll also create missing nodes during scan of e.g.
/proc/consoles

On Fri, Dec 07, 2012 at 09:00:57AM +0100, Werner Fink wrote:
>
> 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@suse.de>
---
configure.ac | 10 +++++++++
lib/consoles.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 76 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 lib/consoles.c lib/consoles.c
index 38c8208..9f0617a 100644
--- lib/consoles.c
+++ lib/consoles.c
@@ -39,6 +39,16 @@
#include <dirent.h>
#include <unistd.h>

+#ifdef USE_EMERGENCY_DEV
+# include <sys/mount.h>
+# include <linux/fs.h>
+# include <linux/magic.h>
+# include <linux/major.h>
+# ifndef MNT_DETACH
+# define MNT_DETACH 2
+# endif
+#endif
+
#include "c.h"
#include "canonicalize.h"
#include "consoles.h"
@@ -77,6 +87,57 @@ dbgprint(const char *mesg, ...)
fputc('\n', stderr);
}

+#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__((__destructor__)) 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 stat rt;
+ struct stat xt;
+ if (mounts) {
+ mounts = 0;
+ return;
+ }
+ if (stat("/", &rt) != 0) {
+ warn("can not get file status of root file system\n");
+ return;
+ }
+ if (stat("/proc", &xt) == 0 && rt.st_dev == xt.st_dev) {
+ if (mount("proc", "/proc", "proc", MS_RELATIME, NULL) == 0)
+ mounts |= MNT_PROCFS;
+ }
+ if (stat("/dev", &xt) == 0 && rt.st_dev == xt.st_dev) {
+ 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"));
+ }
+ }
+ }
+}
+# undef dovoid
+#endif
+
/*
* Read and allocate one line from file,
* the caller has to free the result
@@ -182,6 +243,11 @@ char* scandev(DIR *dir, dev_t comparedev)
continue;
if ((size_t)snprintf(path, sizeof(path), "/dev/%s", dent->d_name) >= sizeof(path))
continue;
+#ifdef USE_EMERGENCY_DEV
+ if (mounts & MNT_DEVTMPFS)
+ (void)mknod(path, S_IFCHR|S_IRUSR|S_IWUSR, comparedev);
+#endif
+
name = canonicalize_path(path);
break;
}
--
1.7.10.4