Disallow refs starting with a non-letter or digit

Change the regexp for validating refs to require at least one letter or digit
before allowing the other special chars in the set `[.-_]`. Names that start
with `.` are traditionally Unix hidden files; let's ignore them under the
assumption they're metadata for some other tool, and we don't want to
potentially conflict with the special `.` and `..` Unix directory entries.
Further, names starting with `-` are problematic for Unix cmdline option
processing; there's no good reason to support that. Finally, disallow `_` just
on general principle - it's simpler to say that ref identifiers must start with
a letter or digit.

We also ignore any existing files (that might be previously created refs) that
start with `.` in the `refs/` directory - there's a Red Hat tool for content
management that injects `.rsync` files, which is why this patch was first
written.

V1: Update to ban all refs starting with a non-letter/digit, and
    also add another call to `ostree_validate_rev` in the pull
    code.

Closes: https://github.com/ostreedev/ostree/issues/1285

Closes: #1286
Approved by: jlebon

tests/test-refs.sh

@@ -23,7 +23,7 @@ set -euo pipefail
 
 setup_fake_remote_repo1 "archive"
 
-echo '1..2'
+echo '1..5'
 
 cd ${test_tmpdir}
 mkdir repo
@@ -88,6 +88,35 @@ if ${CMD_PREFIX} ostree --repo=repo refs foo/ctest --create=ctest; then
     assert_not_reached "refs --create unexpectedly succeeded in overwriting an existing prefix!"
 fi
 
+# https://github.com/ostreedev/ostree/issues/1285
+# One tool was creating .latest_rsync files in each dir, let's ignore stuff like
+# that.
+echo '👻' > repo/refs/heads/.spooky_and_hidden
+${CMD_PREFIX} ostree --repo=repo refs > refs.txt
+assert_not_file_has_content refs.txt 'spooky'
+${CMD_PREFIX} ostree --repo=repo refs ctest --create=exampleos/x86_64/standard
+echo '👻' > repo/refs/heads/exampleos/x86_64/.further_spooky_and_hidden
+${CMD_PREFIX} ostree --repo=repo refs > refs.txt
+assert_file_has_content refs.txt 'exampleos/x86_64/standard'
+assert_not_file_has_content refs.txt 'spooky'
+rm repo/refs/heads/exampleos -rf
+echo "ok hidden refs"
+
+for ref in '.' '-' '.foo' '-bar' '!' '!foo'; do
+    if ${CMD_PREFIX} ostree --repo=repo refs ctest --create=${ref} 2>err.txt; then
+        fatal "Created ref ${ref}"
+    fi
+    assert_file_has_content err.txt 'Invalid ref'
+done
+echo "ok invalid refs"
+
+for ref in 'org.foo.bar/x86_64/standard-blah'; do
+    ostree --repo=repo refs ctest --create=${ref}
+    ostree --repo=repo rev-parse ${ref} >/dev/null
+    ostree --repo=repo refs --delete ${ref}
+done
+echo "ok valid refs with chars '._-'"
+
 #Check to see if any uncleaned tmp files were created after failed --create
 ${CMD_PREFIX} ostree --repo=repo refs | wc -l > refscount.create1
 assert_file_has_content refscount.create1 "^5$"