[Buildd-tools-devel] Bug#427047: schroot: Proposal for global custom mount points specification (different from 395062)

[Peter Rabbitson]

Package: schroot
Version: 1.1.4-1
Severity: wishlist
Tags: patch


Hi,
I have a similar situation to what Kees Cook described in bug #395062. 
However in my case I needed to modify some of the default mounts, specifically
removing /dev/pts and making /dev an --rbind to the system /dev so I can enjoy
the functionality of udev from within the chroot. With the numerous package 
updates last week, I got tired of fixing /etc/schroot/setup.d/10mount to my
liking, so this idea was born. 

The proposal is very simple - I am adding support for an fstab-like file
/etc/scroot/schroot.fstab. The code is totally non-intrusive, and activates
only when the file is present. I think I have covered all the corner cases,
with corresponding non-cryptic error messages. Feel free to include this in 
the distribution if you like the idea.

Cheers

Peter

P.S. I am not that good with shell scripting, a bashism might have slipped in
here or there
-------------- next part --------------
diff -ru /etc/schroot/setup.d.original/00check /etc/schroot/setup.d/00check
--- /etc/schroot/setup.d.original/00check	2007-05-29 01:14:02.000000000 +0200
+++ /etc/schroot/setup.d/00check	2007-06-01 14:41:24.000000000 +0200
@@ -16,6 +16,8 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 # MA  02111-1307  USA
 
+FSTAB="/etc/schroot/schroot.fstab"
+
 if [ $1 = "setup-start" ] || [ $1 = "setup-recover" ]; then
 
     if [ "$AUTH_VERBOSITY" = "verbose" ]; then
@@ -80,4 +82,17 @@
 	exit 1
     fi
 
+    # Check ownership and permissions of schroot.fstab
+    if [ -f "$FSTAB" ]; then
+
+	if [ `stat --printf '%u%g' "$FSTAB"` != "00" ] ; then
+	    echo "$FSTAB must be owned by root"
+	    exit 1
+	fi
+
+	if stat --printf '%A' "$FSTAB" | grep -v '^-.......--$' ; then
+	    echo "$FSTAB can not have write/execute permissions for others"
+	    exit 1
+	fi
+    fi
 fi
diff -ru /etc/schroot/setup.d.original/10mount /etc/schroot/setup.d/10mount
--- /etc/schroot/setup.d.original/10mount	2007-05-29 01:14:02.000000000 +0200
+++ /etc/schroot/setup.d/10mount	2007-06-01 14:57:06.000000000 +0200
@@ -18,6 +18,8 @@
 
 set -e
 
+FSTAB="/etc/schroot/schroot.fstab"
+
 # Mount a filesystem
 # $1: mount options
 # $2: mount device
@@ -39,6 +41,41 @@
     mount $VERBOSE $1 "$2" "$3"
 }
 
+# Mount filesystems described in the local fstab file $FSTAB
+# The full file format specification is supported as described in fstab(5),
+# including UUID and LABEL device/partition specifications.
+#
+# The cat/echo/piping acrobatics is necessary to accomodate files without
+# trailing newlines
+do_mount_fstab()
+{
+    (cat $FSTAB; echo) | 
+    (
+	LN=0
+	while read m_dev m_loc m_type m_opts m_trailing; do
+	    LN=$(($LN+1))
+	    if [ -z $m_dev ] || echo $m_dev | grep -q '^#'; then continue; fi
+
+	    if [ -z $m_loc ] || [ -z $m_type ] ; then 
+		echo "Malformed mount specification in $FSTAB line $LN"
+		exit 1
+	    fi
+
+	    if [ "$m_type" = "ignore" ] ; then continue; fi
+
+	    m_args="-t $m_type"
+            if [ "x$m_opts" != "x" ]; then 
+		m_args="$m_args -o $m_opts"
+	    fi
+
+	    m_dev=$(echo "$m_dev" | sed -e 's/^LABEL=/-L /')
+	    m_dev=$(echo "$m_dev" | sed -e 's/^UUID=/-U /')
+
+	    do_mount "$m_args" "$m_dev" "${CHROOT_PATH}/$m_loc"
+	done
+    )
+}
+
 # Unmount all filesystem under specified location
 # $1: mount base location
 do_umount_all()
@@ -95,11 +132,22 @@
 	fi
 
 	if [ "$CHROOT_TYPE" != "plain" ]; then
-	    do_mount "-t proc"    "proc"     "${CHROOT_PATH}/proc"
-	    do_mount "-o rw,bind" "/dev/pts" "${CHROOT_PATH}/dev/pts"
-	    do_mount "-t tmpfs"   "tmpfs"    "${CHROOT_PATH}/dev/shm"
-	    do_mount "-o rw,bind" "/home"    "${CHROOT_PATH}/home"
-	    do_mount "-o rw,bind" "/tmp"     "${CHROOT_PATH}/tmp"
+	    if [ -f "$FSTAB" ] ; then
+		if [ "$AUTH_VERBOSITY" = "verbose" ]; then
+		    echo "Mounting locations found in $FSTAB:"
+		fi
+		do_mount_fstab
+
+	    else
+		if [ "$AUTH_VERBOSITY" = "verbose" ]; then
+		    echo "No local $FSTAB found, mounting defaults:"
+		fi
+	        do_mount "-t proc"    "proc"     "${CHROOT_PATH}/proc"
+	        do_mount "-o rw,bind" "/dev/pts" "${CHROOT_PATH}/dev/pts"
+	        do_mount "-t tmpfs"   "tmpfs"    "${CHROOT_PATH}/dev/shm"
+	        do_mount "-o rw,bind" "/home"    "${CHROOT_PATH}/home"
+	        do_mount "-o rw,bind" "/tmp"     "${CHROOT_PATH}/tmp"
+	    fi
 	fi
 
     elif [ $1 = "setup-stop" ]; then
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# This is the schroot mount definition file. Its syntax closely follows the
# one of your system fstab, as described in fstab(5), with these EXCEPTIONS:
#
# * Only the first four fields (fs_spec, fs_file, fs_vfstype and fs_mntopts)
#   are significant. Any additional fields like fs_freq and fs_passno are
#   ignored. A side effect of this is that trailing comments are allowed.
#
# * All mount points specified in the second field (fs_file) will be prefixed 
#   with the chroot directory. Thus all mount point paths must be specified as
#   seen from within the chroot.
#

# The following are the default mounts every system is expected to have.
# Be extra careful when modifying them - it might prevent you from logging
# into your new shiny chroot.
 
proc        /proc       proc
/dev/pts    /dev/pts    none    rw,bind
tmpfs       /dev/shm    tmpfs
/home       /home       none    rw,bind
/tmp        /tmp        none    rw,bind