[apparmor] [patch] tests: work around systemd mounting / shared in pivot_root tests

[Tyler Hicks]

On 2015-03-24 14:48:22, Steve Beattie wrote:
> The systemd init daemon mounts the / filesystem as shared [1], which
> breaks pivot_root(2). The following patch adjusts the pivot_root
> test script to remount / as private if it detects that its shared,
> allowing the tests to run successfully, and then undoes it once the
> tests are complete.
> 
> [1] http://cgit.freedesktop.org/systemd/systemd/commit/?id=b3ac5f8cb98757416d8660023d6564a7c411f0a0
> 
> Signed-off-by: Steve Beattie <steve at nxnw.org>
> ---
>  tests/regression/apparmor/pivot_root.sh |   24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> Index: b/tests/regression/apparmor/pivot_root.sh
> ===================================================================
> --- a/tests/regression/apparmor/pivot_root.sh
> +++ b/tests/regression/apparmor/pivot_root.sh
> @@ -25,6 +25,7 @@ put_old=${new_root}put_old/
>  bad=$tmpdir/BAD/
>  proc=$new_root/proc
>  fstype="ext2"
> +root_was_shared="no"
>  
>  pivot_root_cleanup() {
>  	mountpoint -q "$proc"
> @@ -36,9 +37,32 @@ pivot_root_cleanup() {
>  	if [ $? -eq 0 ] ; then
>  		umount "$new_root"
>  	fi
> +
> +	if [ "${root_was_shared}" = "yes" ] ; then
> +		[ -n "$VERBOSE" ] && echo 'notice: re-mounting / as shared'
> +		mount -o remount --make-shared /

I don't think the '-o remount' is needed. I've never used it when
changing a mount's propagation status and the mount(8) man page doesn't
use it in its examples.

I strace'ed mount with and without '-o remount' to see if there's a
difference:

 $ sudo strace mount --make-private / 2>&1 | tail
 fstat(3, {st_mode=S_IFREG|0644, st_size=3165552, ...}) = 0
 mmap(NULL, 3165552, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fed06565000
 close(3)                                = 0
 getuid()                                = 0
 geteuid()                               = 0
 mount("none", "/", NULL, MS_PRIVATE, NULL) = 0
 close(1)                                = 0
 close(2)                                = 0
 exit_group(0)                           = ?
 +++ exited with 0 +++

 $ sudo strace mount -o remount --make-private / 2>&1 | tail
 stat("/sbin/mount.ext3", 0x7ffdf0a11730) = -1 ENOENT (No such file or directory)
 stat("/sbin/fs.d/mount.ext3", 0x7ffdf0a11730) = -1 ENOENT (No such file or directory)
 stat("/sbin/fs/mount.ext3", 0x7ffdf0a11730) = -1 ENOENT (No such file or directory)
 mount("none", "/", 0x18a1210, MS_MGC_VAL|MS_REMOUNT|MS_SILENT, NULL) = 0
 mount("none", "/", NULL, MS_SILENT|MS_PRIVATE, NULL) = 0
 access("/", W_OK)                       = 0
 close(1)                                = 0
 close(2)                                = 0
 exit_group(0)                           = ?
 +++ exited with 0 +++

The '-o remount' ends up being an entirely separate operation that
shouldn't be needed so I think it is best to drop it.

> +	fi
>  }
>  do_onexit="pivot_root_cleanup"
>  
> +# systemd mounts / and everything under it MS_SHARED. This breaks
> +# pivot_root entirely, so attempt to detect it, and remount /
> +# MS_PRIVATE temporarily.
> +FINDMNT=/bin/findmnt
> +if [ -x "${FINDMNT}" ] && ${FINDMNT} -no PROPAGATION / > /dev/null 2>&1 ; then
> +	if [ "$(${FINDMNT} -no PROPAGATION /)" == "shared" ] ; then
> +		root_was_shared="yes"
> +	fi
> +elif [ "$(ps -hp1  -ocomm)" = "systemd" ] ; then
> +	# no findmnt or findmnt doesn't know the PROPAGATION column,
> +	# but init is systemd so assume rootfs is shared
> +	root_was_shared="yes"
> +fi
> +if [ "${root_was_shared}" = "yes" ] ; then
> +	[ -n "$VERBOSE" ] && echo 'notice: re-mounting / as private'
> +	mount -o remount --make-private /

Here, too.

Everything else looks good. Feel free to put my ack on it if you agree
with my proposed changes.

Thanks!

Tyler

> +fi
> +
>  # Create disk image since pivot_root doesn't allow old root and new root to be
>  # on the same filesystem
>  dd if=/dev/zero of="$disk_img" bs=1024 count=512 2> /dev/null
> 
> -- 
> Steve Beattie
> <sbeattie at ubuntu.com>
> http://NxNW.org/~steve/



> -- 
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> AppArmor at lists.ubuntu.com
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