[PATCH v7 3/9] packed-backend: check whether the "packed-refs" is regular file

[shejialuo <shejialuo@gmail.com>]

Although "git-fsck(1)" and "packed-backend.c" will check some
consistency and correctness of "packed-refs" file, they never check the
filetype of the "packed-refs". Let's verify that the "packed-refs" has
the expected filetype, confirming it is created by "git pack-refs"
command.

We could use "open_nofollow" wrapper to open the raw "packed-refs" file.
If the returned "fd" value is less than 0, we could check whether the
"errno" is "ELOOP" to report an error to the user. And then we use
"fstat" to check whether the "packed-refs" file is a regular file.

Reuse "FSCK_MSG_BAD_REF_FILETYPE" fsck message id to report the error to
the user if "packed-refs" is not a regular file.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
---
 refs/packed-backend.c    | 50 +++++++++++++++++++++++++++++++++++++---
 t/t0602-reffiles-fsck.sh | 30 ++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index a7b6f74b6e..f69a0598c7 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -4,6 +4,7 @@
 #include "../git-compat-util.h"
 #include "../config.h"
 #include "../dir.h"
+#include "../fsck.h"
 #include "../gettext.h"
 #include "../hash.h"
 #include "../hex.h"
@@ -1748,15 +1749,58 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 	return empty_ref_iterator_begin();
 }
 
-static int packed_fsck(struct ref_store *ref_store UNUSED,
-		       struct fsck_options *o UNUSED,
+static int packed_fsck(struct ref_store *ref_store,
+		       struct fsck_options *o,
 		       struct worktree *wt)
 {
+	struct packed_ref_store *refs = packed_downcast(ref_store,
+							REF_STORE_READ, "fsck");
+	struct stat st;
+	int ret = 0;
+	int fd;
 
 	if (!is_main_worktree(wt))
 		return 0;
 
-	return 0;
+	if (o->verbose)
+		fprintf_ln(stderr, "Checking packed-refs file %s", refs->path);
+
+	fd = open_nofollow(refs->path, O_RDONLY);
+	if (fd < 0) {
+		/*
+		 * If the packed-refs file doesn't exist, there's nothing
+		 * to check.
+		 */
+		if (errno == ENOENT)
+			goto cleanup;
+
+		if (errno == ELOOP) {
+			struct fsck_ref_report report = { 0 };
+			report.path = "packed-refs";
+			ret = fsck_report_ref(o, &report,
+					      FSCK_MSG_BAD_REF_FILETYPE,
+					      "not a regular file but a symlink");
+			goto cleanup;
+		}
+
+		ret = error_errno(_("unable to open '%s'"), refs->path);
+		goto cleanup;
+	} else if (fstat(fd, &st) < 0) {
+		ret = error_errno(_("unable to stat '%s'"), refs->path);
+		goto cleanup;
+	} else if (!S_ISREG(st.st_mode)) {
+		struct fsck_ref_report report = { 0 };
+		report.path = "packed-refs";
+		ret = fsck_report_ref(o, &report,
+				      FSCK_MSG_BAD_REF_FILETYPE,
+				      "not a regular file");
+		goto cleanup;
+	}
+
+cleanup:
+	if (fd >= 0)
+		close(fd);
+	return ret;
 }
 
 struct ref_storage_be refs_be_packed = {
diff --git a/t/t0602-reffiles-fsck.sh b/t/t0602-reffiles-fsck.sh
index cf7a202d0d..68b7d4999e 100755
--- a/t/t0602-reffiles-fsck.sh
+++ b/t/t0602-reffiles-fsck.sh
@@ -617,4 +617,34 @@ test_expect_success 'ref content checks should work with worktrees' '
 	)
 '
 
+test_expect_success SYMLINKS 'the filetype of packed-refs should be checked' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit default &&
+		git branch branch-1 &&
+		git branch branch-2 &&
+		git branch branch-3 &&
+		git pack-refs --all &&
+
+		mv .git/packed-refs .git/packed-refs-back &&
+		ln -sf packed-refs-back .git/packed-refs &&
+		test_must_fail git refs verify 2>err &&
+		cat >expect <<-EOF &&
+		error: packed-refs: badRefFiletype: not a regular file but a symlink
+		EOF
+		rm .git/packed-refs &&
+		test_cmp expect err &&
+
+		mkdir .git/packed-refs &&
+		test_must_fail git refs verify 2>err &&
+		cat >expect <<-EOF &&
+		error: packed-refs: badRefFiletype: not a regular file
+		EOF
+		rm -r .git/packed-refs &&
+		test_cmp expect err
+	)
+'
+
 test_done
-- 
2.48.1