lib/commit: Fix hardlink checkout commit with bare-user + mod xattrs

This is more subtle fallout from:
https://github.com/ostreedev/ostree/pull/1170
AKA commit: 8fe45362578a43260876134d6547ebd0bb2485c3

Before, if we found a devino cache hit, we'd use it unconditionally.

Recall that `bare-user` repositories are very special in that they're the only
mode where the on disk state ("physical state") is not the "real" state. The
latter is stored in the `user.ostreemeta` xattr. (`bare-user` repos are also
highly special in that symlinks are regular files physically, but that's not
immediately relevant here).

Since we now have `bare-user-only` for the "pure unprivileged container" case,
`bare-user` should just be used for "OS builds" which have nonzero uids (and
possibly SELinux labels etc.)

In an experimental tool I'm writing "skopeo2ostree" which imports OCI images
into refs, then squashes them together into a single final commit, we lost the
the `81` group ID for `/usr/libexec/dbus-1/dbus-daemon-launch-helper`.

This happened because the commit code was loading the "physical" disk state,
where the uid/gid are zero because that's the uid I happened to be using. We
didn't just directly do the link speedup because I was using `--selinux-policy`
which caused the xattrs to change, which caused us to re-commit objects from the
physical state.

The unit test I added actually doesn't quite trigger this, but I left
it because "why not".  Really testing this requires the installed test
which uses SELinux policy from `/`.

The behavior without this fix looks like:

```
-00755 0 0     12 { [(b'user.ostreemeta', [byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x51, 0x00, 0x00, 0x81, 0xed]), (b'security.selinux', b'system_u:object_r:lib_t:s0')] } /usr/lib/dbus-daemon-helper
```

which was obviously totally broken - we shouldn't be picking up the
`user.ostreemeta` xattr and actually committing it of course.

Closes: #1297
Approved by: jlebon

1 files changed, 27 insertions, 1 deletions

diff --git a/tests/test-basic-user.sh b/tests/test-basic-user.sh
index 291806c8..bc08b65a 100755
--- a/tests/test-basic-user.sh
+++ b/tests/test-basic-user.sh
@@ -25,7 +25,7 @@ skip_without_user_xattrs
 
 setup_test_repository "bare-user"
 
-extra_basic_tests=4
+extra_basic_tests=5
 . $(dirname $0)/basic-test.sh
 
 # Reset things so we don't inherit a lot of state from earlier tests
@@ -73,3 +73,29 @@ rm test2-checkout -rf
 $OSTREE checkout -U -H test2-unreadable test2-checkout
 assert_file_has_mode test2-checkout/unreadable 400
 echo "ok bare-user handled unreadable file"
+
+cd ${test_tmpdir}
+mkdir -p components/{dbus,systemd}/usr/{bin,lib}
+echo dbus binary > components/dbus/usr/bin/dbus-daemon
+chmod a+x components/dbus/usr/bin/dbus-daemon
+echo dbus lib > components/dbus/usr/lib/libdbus.so.1
+echo dbus helper > components/dbus/usr/lib/dbus-daemon-helper
+chmod a+x components/dbus/usr/lib/dbus-daemon-helper
+echo systemd binary > components/systemd/usr/bin/systemd
+chmod a+x components/systemd/usr/bin/systemd
+echo systemd lib > components/systemd/usr/lib/libsystemd.so.1
+
+# Make the gid on dbus 81 like fedora
+$OSTREE commit -b component-dbus --owner-uid 0 --owner-gid 81 --tree=dir=components/dbus
+$OSTREE commit -b component-systemd --owner-uid 0 --owner-gid 0 --tree=dir=components/systemd
+rm rootfs -rf
+for component in dbus systemd; do
+    $OSTREE checkout -U -H component-${component} --union rootfs
+done
+echo 'some rootfs data' > rootfs/usr/lib/cache.txt
+$OSTREE commit -b rootfs --link-checkout-speedup --tree=dir=rootfs
+$OSTREE ls rootfs /usr/bin/systemd >ls.txt
+assert_file_has_content ls.txt '^-007.. 0 0 .*/usr/bin/systemd'
+$OSTREE ls rootfs /usr/lib/dbus-daemon-helper >ls.txt
+assert_file_has_content ls.txt '^-007.. 0 81 .*/usr/lib/dbus-daemon-helper'
+echo "ok bare-user link-checkout-speedup maintains uids"