ref: add more strict checks for regular refs

We have already used "parse_loose_ref_contents" function to check
whether the ref content is valid in files backend. However, by
using "parse_loose_ref_contents", we allow the ref's content to end with
garbage or without a newline.

Even though we never create such loose refs ourselves, we have accepted
such loose refs. So, it is entirely possible that some third-party tools
may rely on such loose refs being valid. We should not report an error
fsck message at current. We should notify the users about such
"curiously formatted" loose refs so that adequate care is taken before
we decide to tighten the rules in the future.

And it's not suitable either to report a warn fsck message to the user.
We don't yet want the "--strict" flag that controls this bit to end up
generating errors for such weirdly-formatted reference contents, as we
first want to assess whether this retroactive tightening will cause
issues for any tools out there. It may cause compatibility issues which
may break the repository. So, we add the following two fsck infos to
represent the situation where the ref content ends without newline or
has trailing garbages:

1. refMissingNewline(INFO): A loose ref that does not end with
   newline(LF).
2. trailingRefContent(INFO): A loose ref has trailing content.

It might appear that we can't provide the user with any warnings by
using FSCK_INFO. However, in "fsck.c::fsck_vreport", we will convert
FSCK_INFO to FSCK_WARN and we can still warn the user about these
situations when using "git refs verify" without introducing
compatibility issues.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 23 insertions, 3 deletions

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 9f300a7d3c..3d4d612420 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -569,7 +569,7 @@ stat_ref:
 	buf = sb_contents.buf;
 
 	ret = parse_loose_ref_contents(ref_store->repo->hash_algo, buf,
-				       oid, referent, type, &myerr);
+				       oid, referent, type, NULL, &myerr);
 
 out:
 	if (ret && !myerr)
@@ -606,7 +606,7 @@ static int files_read_symbolic_ref(struct ref_store *ref_store, const char *refn
 int parse_loose_ref_contents(const struct git_hash_algo *algop,
 			     const char *buf, struct object_id *oid,
 			     struct strbuf *referent, unsigned int *type,
-			     int *failure_errno)
+			     const char **trailing, int *failure_errno)
 {
 	const char *p;
 	if (skip_prefix(buf, "ref:", &buf)) {
@@ -628,6 +628,10 @@ int parse_loose_ref_contents(const struct git_hash_algo *algop,
 		*failure_errno = EINVAL;
 		return -1;
 	}
+
+	if (trailing)
+		*trailing = p;
+
 	return 0;
 }
 
@@ -3513,6 +3517,7 @@ static int files_fsck_refs_content(struct ref_store *ref_store,
 	struct strbuf ref_content = STRBUF_INIT;
 	struct strbuf referent = STRBUF_INIT;
 	struct fsck_ref_report report = { 0 };
+	const char *trailing = NULL;
 	unsigned int type = 0;
 	int failure_errno = 0;
 	struct object_id oid;
@@ -3537,7 +3542,7 @@ static int files_fsck_refs_content(struct ref_store *ref_store,
 
 	if (parse_loose_ref_contents(ref_store->repo->hash_algo,
 				     ref_content.buf, &oid, &referent,
-				     &type, &failure_errno)) {
+				     &type, &trailing, &failure_errno)) {
 		strbuf_rtrim(&ref_content);
 		ret = fsck_report_ref(o, &report,
 				      FSCK_MSG_BAD_REF_CONTENT,
@@ -3545,6 +3550,21 @@ static int files_fsck_refs_content(struct ref_store *ref_store,
 		goto cleanup;
 	}
 
+	if (!(type & REF_ISSYMREF)) {
+		if (!*trailing) {
+			ret = fsck_report_ref(o, &report,
+					      FSCK_MSG_REF_MISSING_NEWLINE,
+					      "misses LF at the end");
+			goto cleanup;
+		}
+		if (*trailing != '\n' || *(trailing + 1)) {
+			ret = fsck_report_ref(o, &report,
+					      FSCK_MSG_TRAILING_REF_CONTENT,
+					      "has trailing garbage: '%s'", trailing);
+			goto cleanup;
+		}
+	}
+
 cleanup:
 	strbuf_release(&ref_content);
 	strbuf_release(&referent);