[PATCH v2 4/5] refs/reftable: add fsck check for trailing newline

From: Karthik Nayak <karthik.188@gmail.com>
Date: Sep 2, 2025, 07:05 UTC
Message-ID: <20250902-228-reftable-introduce-consistency-checks-v2-4-4f96b3834779@gmail.com>
In-Reply-To: <20250902-228-reftable-introduce-consistency-checks-v2-0-4f96b3834779@gmail.com>

Introduce a fsck check for the reftable backend, which checks if the 'tables.list' contains a newline. The reftable backend writes a trailing newline when writing the 'tables.list', but it doesn't check for it when reading the file. A missing newline however indicates that the file was manually tampered with, so let's raise this as an error to the user.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 Documentation/fsck-msgids.adoc |  3 +++
 fsck.h                         |  1 +
 refs/reftable-backend.c        |  3 +++
 reftable/fsck.c                | 36 ++++++++++++++++++++++++++++++++++++
 reftable/reftable-fsck.h       |  2 ++
 t/t0614-reftable-fsck.sh       | 21 +++++++++++++++++++++
 6 files changed, 66 insertions(+)

diff --git a/Documentation/fsck-msgids.adoc b/Documentation/fsck-msgids.adoc
index 707e2fc50a..1432b1de06 100644
--- a/Documentation/fsck-msgids.adoc
+++ b/Documentation/fsck-msgids.adoc
@@ -41,6 +41,9 @@
 `badReftableStackCount`::
 	(ERROR) Mismatch in number of tables.
 
+`badReftableStackListNewline`::
+	(ERROR) Reftable stack list missing trailing newline.
+
 `badReftableTableName`::
 	(ERROR) A reftable table has an invalid name.
 
diff --git a/fsck.h b/fsck.h
index 256effc4f8..33432bae79 100644
--- a/fsck.h
+++ b/fsck.h
@@ -35,6 +35,7 @@ enum fsck_msg_type {
 	FUNC(BAD_PARENT_SHA1, ERROR)                               \
 	FUNC(BAD_REFERENT_NAME, ERROR)                             \
 	FUNC(BAD_REFTABLE_STACK_COUNT, ERROR)                      \
+	FUNC(BAD_REFTABLE_STACK_LIST_NEWLINE, ERROR)               \
 	FUNC(BAD_REFTABLE_TABLE_NAME, ERROR)                       \
 	FUNC(BAD_REF_CONTENT, ERROR)                               \
 	FUNC(BAD_REF_FILETYPE, ERROR)                              \
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 59c39f9b52..7331513b19 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -2698,6 +2698,9 @@ static int reftable_fsck_error_handler(struct reftable_fsck_info *info,
 	case REFTABLE_FSCK_ERROR_STACK_COUNT:
 		msg_id = FSCK_MSG_BAD_REFTABLE_STACK_COUNT;
 		break;
+	case REFTABLE_FSCK_ERROR_STACK_LIST_MISSING_NEWLINE:
+		msg_id = FSCK_MSG_BAD_REFTABLE_STACK_LIST_NEWLINE;
+		break;
 	default:
 		BUG("unknown fsck error: %d", info->error);
 	}
diff --git a/reftable/fsck.c b/reftable/fsck.c
index 20e6bfb0f1..9a7f22c56b 100644
--- a/reftable/fsck.c
+++ b/reftable/fsck.c
@@ -1,7 +1,31 @@
 #include "basics.h"
+#include "reftable-error.h"
 #include "reftable-fsck.h"
 #include "stack.h"
 
+static int reftable_fsck_stack_contains_newline(const char *list_file)
+{
+	FILE *f = fopen(list_file, "r");
+	int c = 0;
+
+	if (f == NULL) {
+		if (errno == ENOENT)
+			return 0;
+		return REFTABLE_IO_ERROR;
+	}
+
+	if (fseek(f, 0, SEEK_END) == 0) {
+		long size = ftell(f);
+		if (size <= 0)
+			return REFTABLE_IO_ERROR;
+		fseek(f, -1, SEEK_END);
+		c = fgetc(f);
+	}
+	fclose(f);
+
+	return c == '\n';
+}
+
 static int reftable_fsck_valid_stack_count(struct reftable_stack *st)
 {
 	DIR *dir = opendir(st->reftable_dir);
@@ -69,6 +93,18 @@ int reftable_fsck_check(struct reftable_stack *stack,
 		}
 	}
 
+	verbose_fn("Checking trailing newline in stack list", cb_data);
+
+	if (!reftable_fsck_stack_contains_newline(stack->list_file)) {
+		struct reftable_fsck_info info = {
+			.error = REFTABLE_FSCK_ERROR_STACK_LIST_MISSING_NEWLINE,
+			.path = "reftable/tables.list",
+			.msg = "trailing newline missing in stack list"
+		};
+
+		err = report_fn(&info, cb_data);
+	}
+
 	verbose_fn("Checking reftable tables count", cb_data);
 
 	if (!reftable_fsck_valid_stack_count(stack)) {
diff --git a/reftable/reftable-fsck.h b/reftable/reftable-fsck.h
index beba1bdd1a..17df661da8 100644
--- a/reftable/reftable-fsck.h
+++ b/reftable/reftable-fsck.h
@@ -8,6 +8,8 @@ enum reftable_fsck_error {
 	REFTABLE_FSCK_ERROR_TABLE_NAME = -1,
 	/* Incorrect number of tables present */
 	REFTABLE_FSCK_ERROR_STACK_COUNT = -2,
+	/* Newline missing at the end of the stack list */
+	REFTABLE_FSCK_ERROR_STACK_LIST_MISSING_NEWLINE = -3,
 };
 
 /* Represents an individual error encountered during the FSCK checks. */
diff --git a/t/t0614-reftable-fsck.sh b/t/t0614-reftable-fsck.sh
index 3a34a31890..3b119eae62 100755
--- a/t/t0614-reftable-fsck.sh
+++ b/t/t0614-reftable-fsck.sh
@@ -75,4 +75,25 @@ test_expect_success 'table count should be checked' '
 	)
 '
 
+test_expect_success 'stack list must contain trailing newline' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		git commit --allow-empty -m initial &&
+
+		git refs verify 2>err &&
+		test_must_be_empty err &&
+
+		printf "%s" "$(cat .git/reftable/tables.list)" >.git/reftable/tables.list.tmp &&
+		mv .git/reftable/tables.list.tmp .git/reftable/tables.list &&
+
+		test_must_fail git refs verify 2>err &&
+		cat >expect <<-EOF &&
+		error: reftable/tables.list: badReftableStackListNewline: trailing newline missing in stack list
+		EOF
+		test_cmp expect err
+	)
+'
+
 test_done

-- 
2.50.1