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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,170 @@ | ||
| #!/bin/bash | ||
| # Add bind mounts in a user namespace and change to that space. | ||
| # Requires being able to run unshare -rm and the ability to do fuse mounts | ||
| # (kernel >= 4.18) and requires fuse-overlayfs. | ||
| # Written by Dave Dykstra November 2024, based heavily on cvmfsexec. | ||
|
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||
| #set -x | ||
| #PS4='c$$+ ' | ||
|
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| VERSION=4.42 | ||
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||
| usage() | ||
| { | ||
| echo "Usage: bindexec [-v] [src:dest ...] -- [command]" >&2 | ||
| echo " Bind mount each src to dest in new user mount namespace" >&2 | ||
| echo " -v: print current version and exit" >&2 | ||
| exit 1 | ||
| } | ||
|
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||
| # needed for pivot_root | ||
| PATH=$PATH:/usr/sbin | ||
|
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| TMPD="$(mktemp -d /dev/shm/bindexec.XXXXXXXXXX)" | ||
| trap "rm -rf $TMPD" 0 # note that trap does not carry past exec | ||
| STARTFIFO=$TMPD/start | ||
| WAITFIFO=$TMPD/wait | ||
| mkfifo $STARTFIFO $WAITFIFO | ||
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||
| # bash syntax {NAME}<&N doesn't work on older bashes such as the | ||
| # version 3.2.x on macOS Big Sur, and in fact it fails with an error | ||
| # message but not an error code, so test for it first to be able to | ||
| # gracefully die | ||
|
|
||
| if [ -n "$({TESTX}<&0 2>&1)" ]; then | ||
| echo "Cannot assign file descriptors to variables, bash version too old" >&2 | ||
| exit 1 | ||
| fi | ||
|
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||
| # make a copy of stdin fd, for sending to the final command | ||
| exec {STDINCOPYFD}<&0 | ||
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| ORIGPWD=$PWD | ||
|
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||
| # can't use OPTIND because it can't distinguish between -- there or missing | ||
| NOPTS=0 | ||
| while getopts "v" OPTION; do | ||
| let NOPTS+=1 | ||
| case $OPTION in | ||
| v) echo "$VERSION" | ||
| exit | ||
| ;; | ||
| \?) usage | ||
| ;; | ||
| esac | ||
| done | ||
| shift $NOPTS | ||
|
|
||
| BINDS="" | ||
| for ARG; do | ||
| if [ "$ARG" == "--" ]; then | ||
| break | ||
| fi | ||
| if [[ "$ARG" != *:* ]]; then | ||
| usage | ||
| fi | ||
| BINDS="$BINDS $ARG" | ||
| shift | ||
| done | ||
|
|
||
| if [ "$ARG" != "--" ]; then | ||
| usage | ||
| fi | ||
| shift | ||
|
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||
| ORIGUID="$(id -u)" | ||
| ORIGGID="$(id -g)" | ||
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| # Note that within the HERE document, unprotected $ substitutions are | ||
| # done by the surrounding shell, and \$ is within the unshare shell | ||
| unshare -rm -pf /bin/bash /dev/stdin "${@:-$SHELL}" <<!EOF-1! | ||
| #set -x | ||
| #PS4='c\$$+ ' | ||
| # now in the first "fake root" namespace | ||
| mount -t proc proc /proc | ||
| mkdir -p $TMPD/upper $TMPD/work $TMPD/overlay | ||
| # put the bind mounts into the upper dir | ||
| for BIND in $BINDS; do | ||
| SRC="\${BIND%:*}" | ||
| DST="\${BIND#*:}" | ||
| if [ -d "\$SRC" ]; then | ||
| mkdir -p $TMPD/upper/\$DST | ||
| elif [ -f "\$SRC" ]; then | ||
| DSTDIR="\${DST%/*}" | ||
| if [ "\$DST" != "\$DSTDIR" ]; then | ||
| mkdir -p $TMPD/upper/\$DSTDIR | ||
| fi | ||
| touch $TMPD/upper/\$DST | ||
| else | ||
| echo "bindexec: \$SRC not found, skipping" >&2 | ||
| fi | ||
| mount --bind \$SRC $TMPD/upper/\$DST | ||
| done | ||
| # Leave this bash running as PID 1, because most other | ||
| # programs won't handle signals & child reaping correctly. | ||
| # Note that all other processes in the namespaces will get | ||
| # a SIGKILL when PID 1 exits. | ||
| trap "" 1 2 3 15 # ignore all ordinary signals | ||
| fuse-overlayfs -o lowerdir=/,upperdir=$TMPD/upper,workdir=$TMPD/work $TMPD/overlay 2> >(grep -v lazytime >&2) | ||
| # put original system dirs on top of the overlay | ||
| mount -t proc proc $TMPD/overlay/proc | ||
| mount --rbind /sys $TMPD/overlay/sys | ||
| mount --rbind /dev $TMPD/overlay/dev | ||
| mount --rbind /run $TMPD/overlay/run | ||
| # also overlay nfs mounts because they don't work through overlay | ||
| mount|while read FROM X TO X TYPE REST; do | ||
| if [[ \$TYPE = nfs* ]]; then | ||
| mkdir -p $TMPD/overlay/\$TO | ||
| mount --bind \$TO $TMPD/overlay/\$TO | ||
| fi | ||
| done | ||
| # Start a second fake root namespace so we don't interfere with the | ||
| # fuse-overlayfs mount space when we do the pivot_root. | ||
| # Quoting the HERE document's delimeter makes this nested shell not | ||
| # interpret $ substitutions, but the previous one still does so | ||
| # need to use \$ when don't want first shell to expand. | ||
| unshare -rm /bin/bash /dev/stdin "\${@:-$SHELL}" <<'!EOF-2!' | ||
| #set -x | ||
| #PS4='c\$$+ ' | ||
| ( | ||
| # This is a background process for setting up the child's uid map | ||
| trap "" 1 2 3 15 # ignore ordinary signals | ||
| read PID | ||
| # set up uid/gid map | ||
| echo "$ORIGGID 0 1" >/proc/"\$PID"/gid_map | ||
| echo "$ORIGUID 0 1" >/proc/"\$PID"/uid_map | ||
| echo "ready" >$WAITFIFO | ||
| ) <$STARTFIFO & | ||
| # Change to the new root. Would use chroot but it doesn't work. | ||
| mount --rbind $TMPD/overlay $TMPD/overlay # pivot_root requires this | ||
| cd $TMPD/overlay | ||
| mkdir -p .old-root | ||
| pivot_root . .old-root | ||
| cd $ORIGPWD | ||
| # Finally, start the user namespace with the original uid/gid | ||
| # This HERE document is also quoted and so the shell does not expand | ||
| exec unshare -U /bin/bash /dev/stdin "\${@:-$SHELL}" <<'!EOF-3!' | ||
| #set -x | ||
| #PS4='c\$$+ ' | ||
| # now in the user namespace | ||
| echo "\$$" >$STARTFIFO | ||
| # wait for the uid/gid maps to be set up | ||
| read X <$WAITFIFO | ||
| exec "\$@" <&$STDINCOPYFD $STDINCOPYFD<&- | ||
| !EOF-3! | ||
| !EOF-2! | ||
| !EOF-1! |
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