mount: -T OTHERTAB support

function                                             old     new   delta
mount_main                                          1221    1241     +20
packed_usage                                       30616   30610      -6

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Signed-off-by: Isaac Dunham <ibid.ag@gmail.com>

2 files changed, 108 insertions, 94 deletions

diff --git a/util-linux/Config.src b/util-linux/Config.src
index c1cd6daa4..854b3682e 100644
--- a/util-linux/Config.src
+++ b/util-linux/Config.src
@@ -434,94 +434,6 @@ config MORE
           you will probably find this utility very helpful. If you don't have
           any need to reading text files, you can leave this disabled.
 
-config MOUNT
-        bool "mount"
-        default y
-        select PLATFORM_LINUX
-        help
-          All files and filesystems in Unix are arranged into one big directory
-          tree. The 'mount' utility is used to graft a filesystem onto a
-          particular part of the tree. A filesystem can either live on a block
-          device, or it can be accessible over the network, as is the case with
-          NFS filesystems. Most people using BusyBox will also want to enable
-          the 'mount' utility.
-
-config FEATURE_MOUNT_FAKE
-        bool "Support option -f"
-        default y
-        depends on MOUNT
-        help
-          Enable support for faking a file system mount.
-
-config FEATURE_MOUNT_VERBOSE
-        bool "Support option -v"
-        default y
-        depends on MOUNT
-        help
-          Enable multi-level -v[vv...] verbose messages. Useful if you
-          debug mount problems and want to see what is exactly passed
-          to the kernel.
-
-config FEATURE_MOUNT_HELPERS
-        bool "Support mount helpers"
-        default n
-        depends on MOUNT
-        help
-          Enable mounting of virtual file systems via external helpers.
-          E.g. "mount obexfs#-b00.11.22.33.44.55 /mnt" will in effect call
-          "obexfs -b00.11.22.33.44.55 /mnt"
-          Also "mount -t sometype [-o opts] fs /mnt" will try
-          "sometype [-o opts] fs /mnt" if simple mount syscall fails.
-          The idea is to use such virtual filesystems in /etc/fstab.
-
-config FEATURE_MOUNT_LABEL
-        bool "Support specifying devices by label or UUID"
-        default y
-        depends on MOUNT
-        select VOLUMEID
-        help
-          This allows for specifying a device by label or uuid, rather than by
-          name. This feature utilizes the same functionality as blkid/findfs.
-          This also enables label or uuid support for swapon.
-
-config FEATURE_MOUNT_NFS
-        bool "Support mounting NFS file systems on Linux < 2.6.23"
-        default n
-        depends on MOUNT
-        select FEATURE_HAVE_RPC
-        select FEATURE_SYSLOG
-        help
-          Enable mounting of NFS file systems on Linux kernels prior
-          to version 2.6.23. Note that in this case mounting of NFS
-          over IPv6 will not be possible.
-
-          Note that this option links in RPC support from libc,
-          which is rather large (~10 kbytes on uclibc).
-
-config FEATURE_MOUNT_CIFS
-        bool "Support mounting CIFS/SMB file systems"
-        default y
-        depends on MOUNT
-        help
-          Enable support for samba mounts.
-
-config FEATURE_MOUNT_FLAGS
-        depends on MOUNT
-        bool "Support lots of -o flags in mount"
-        default y
-        help
-          Without this, mount only supports ro/rw/remount. With this, it
-          supports nosuid, suid, dev, nodev, exec, noexec, sync, async, atime,
-          noatime, diratime, nodiratime, loud, bind, move, shared, slave,
-          private, unbindable, rshared, rslave, rprivate, and runbindable.
-
-config FEATURE_MOUNT_FSTAB
-        depends on MOUNT
-        bool "Support /etc/fstab and -a"
-        default y
-        help
-          Support mount all and looking for files in /etc/fstab.
-
 config PIVOT_ROOT
         bool "pivot_root"
         default y
diff --git a/util-linux/mount.c b/util-linux/mount.c
index 62fd41fd7..fbc89c862 100644
--- a/util-linux/mount.c
+++ b/util-linux/mount.c
@@ -17,8 +17,103 @@
 // mount_it_now() does the actual mount.
 //
 
+//config:config MOUNT
+//config:       bool "mount"
+//config:       default y
+//config:       select PLATFORM_LINUX
+//config:       help
+//config:         All files and filesystems in Unix are arranged into one big directory
+//config:         tree. The 'mount' utility is used to graft a filesystem onto a
+//config:         particular part of the tree. A filesystem can either live on a block
+//config:         device, or it can be accessible over the network, as is the case with
+//config:         NFS filesystems. Most people using BusyBox will also want to enable
+//config:         the 'mount' utility.
+//config:
+//config:config FEATURE_MOUNT_FAKE
+//config:       bool "Support option -f"
+//config:       default y
+//config:       depends on MOUNT
+//config:       help
+//config:         Enable support for faking a file system mount.
+//config:
+//config:config FEATURE_MOUNT_VERBOSE
+//config:       bool "Support option -v"
+//config:       default y
+//config:       depends on MOUNT
+//config:       help
+//config:         Enable multi-level -v[vv...] verbose messages. Useful if you
+//config:         debug mount problems and want to see what is exactly passed
+//config:         to the kernel.
+//config:
+//config:config FEATURE_MOUNT_HELPERS
+//config:       bool "Support mount helpers"
+//config:       default n
+//config:       depends on MOUNT
+//config:       help
+//config:         Enable mounting of virtual file systems via external helpers.
+//config:         E.g. "mount obexfs#-b00.11.22.33.44.55 /mnt" will in effect call
+//config:         "obexfs -b00.11.22.33.44.55 /mnt"
+//config:         Also "mount -t sometype [-o opts] fs /mnt" will try
+//config:         "sometype [-o opts] fs /mnt" if simple mount syscall fails.
+//config:         The idea is to use such virtual filesystems in /etc/fstab.
+//config:
+//config:config FEATURE_MOUNT_LABEL
+//config:       bool "Support specifying devices by label or UUID"
+//config:       default y
+//config:       depends on MOUNT
+//config:       select VOLUMEID
+//config:       help
+//config:         This allows for specifying a device by label or uuid, rather than by
+//config:         name. This feature utilizes the same functionality as blkid/findfs.
+//config:         This also enables label or uuid support for swapon.
+//config:
+//config:config FEATURE_MOUNT_NFS
+//config:       bool "Support mounting NFS file systems on Linux < 2.6.23"
+//config:       default n
+//config:       depends on MOUNT
+//config:       select FEATURE_HAVE_RPC
+//config:       select FEATURE_SYSLOG
+//config:       help
+//config:         Enable mounting of NFS file systems on Linux kernels prior
+//config:         to version 2.6.23. Note that in this case mounting of NFS
+//config:         over IPv6 will not be possible.
+//config:
+//config:         Note that this option links in RPC support from libc,
+//config:         which is rather large (~10 kbytes on uclibc).
+//config:
+//config:config FEATURE_MOUNT_CIFS
+//config:       bool "Support mounting CIFS/SMB file systems"
+//config:       default y
+//config:       depends on MOUNT
+//config:       help
+//config:         Enable support for samba mounts.
+//config:
+//config:config FEATURE_MOUNT_FLAGS
+//config:       depends on MOUNT
+//config:       bool "Support lots of -o flags in mount"
+//config:       default y
+//config:       help
+//config:         Without this, mount only supports ro/rw/remount. With this, it
+//config:         supports nosuid, suid, dev, nodev, exec, noexec, sync, async, atime,
+//config:         noatime, diratime, nodiratime, loud, bind, move, shared, slave,
+//config:         private, unbindable, rshared, rslave, rprivate, and runbindable.
+//config:
+//config:config FEATURE_MOUNT_FSTAB
+//config:       depends on MOUNT
+//config:       bool "Support /etc/fstab and -a"
+//config:       default y
+//config:       help
+//config:         Support mount all and looking for files in /etc/fstab.
+//config:
+//config:config FEATURE_MOUNT_OTHERTAB
+//config:       depends on FEATURE_MOUNT_FSTAB
+//config:       bool "Support -T <alt_fstab>"
+//config:       default y
+//config:       help
+//config:         Support mount -T (specifying an alternate fstab)
+
 //usage:#define mount_trivial_usage
-//usage:       "[OPTIONS] [-o OPTS] DEVICE NODE"
+//usage:       "[OPTIONS] [-o OPT] DEVICE NODE"
 //usage:#define mount_full_usage "\n\n"
 //usage:       "Mount a filesystem. Filesystem autodetection requires /proc.\n"
 //usage:     "\n        -a              Mount all filesystems in fstab"
@@ -41,8 +136,11 @@
 //usage:        )
 ////usage:   "\n        -s              Sloppy (ignored)"
 //usage:     "\n        -r              Read-only mount"
-//usage:     "\n        -w              Read-write mount (default)"
+////usage:     "\n      -w              Read-write mount (default)"
 //usage:     "\n        -t FSTYPE[,...] Filesystem type(s)"
+//usage:        IF_FEATURE_MOUNT_OTHERTAB(
+//usage:     "\n        -T FILE         Read FILE instead of /etc/fstab"
+//usage:        )
 //usage:     "\n        -O OPT          Mount only filesystems with option OPT (-a only)"
 //usage:     "\n-o OPT:"
 //usage:        IF_FEATURE_MOUNT_LOOP(
@@ -64,7 +162,7 @@
 //usage:     "\n        move            Relocate an existing mount point"
 //usage:        )
 //usage:     "\n        remount         Remount a mounted filesystem, changing flags"
-//usage:     "\n        ro/rw           Same as -r/-w"
+//usage:     "\n        ro              Same as -r"
 //usage:     "\n"
 //usage:     "\nThere are filesystem-specific -o flags."
 //usage:
@@ -167,7 +265,7 @@ enum {
 };
 
 
-#define OPTION_STR "o:t:rwanfvsiO:"
+#define OPTION_STR "o:t:rwanfvsiO:" IF_FEATURE_MOUNT_OTHERTAB("T:")
 enum {
         OPT_o = (1 << 0),
         OPT_t = (1 << 1),
@@ -180,6 +278,7 @@ enum {
         OPT_s = (1 << 8),
         OPT_i = (1 << 9),
         OPT_O = (1 << 10),
+        OPT_T = (1 << 11),
 };
 
 #if ENABLE_FEATURE_MTAB_SUPPORT
@@ -2034,7 +2133,7 @@ int mount_main(int argc UNUSED_PARAM, char **argv)
         char *O_optmatch = NULL;
         char *storage_path;
         llist_t *lst_o = NULL;
-        const char *fstabname;
+        const char *fstabname = "/etc/fstab";
         FILE *fstab;
         int i, j;
         int rc = EXIT_SUCCESS;
@@ -2061,6 +2160,7 @@ int mount_main(int argc UNUSED_PARAM, char **argv)
         // Max 2 params; -o is a list, -v is a counter
         opt_complementary = "?2o::" IF_FEATURE_MOUNT_VERBOSE("vv");
         opt = getopt32(argv, OPTION_STR, &lst_o, &fstype, &O_optmatch
+                        IF_FEATURE_MOUNT_OTHERTAB(, &fstabname)
                         IF_FEATURE_MOUNT_VERBOSE(, &verbose));
         while (lst_o) append_mount_options(&cmdopts, llist_pop(&lst_o)); // -o
         if (opt & OPT_r) append_mount_options(&cmdopts, "ro"); // -r
@@ -2128,8 +2228,10 @@ int mount_main(int argc UNUSED_PARAM, char **argv)
                 return rc;
         }
 
+        // A malicious user could overmount /usr without this.
+        if (ENABLE_FEATURE_MOUNT_OTHERTAB && nonroot)
+                fstabname = "/etc/fstab";
         // Open either fstab or mtab
-        fstabname = "/etc/fstab";
         if (cmdopt_flags & MS_REMOUNT) {
                 // WARNING. I am not sure this matches util-linux's
                 // behavior. It's possible util-linux does not