[PATCH 3/6] Make sure fsck_commit_buffer() does not run out of the buffer

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Aug 28, 2014, 14:46 UTC
Message-ID: <alpine.DEB.1.00.1408281646450.990@s15462909.onlinehome-server.info>
In-Reply-To: <alpine.DEB.1.00.1408171840040.990@s15462909.onlinehome-server.info>

So far, we assumed that the buffer is NUL terminated, but this is not a safe assumption, now that we opened the fsck_object() API to pass a buffer directly.

So let's make sure that there is at least an empty line in the buffer. That way, our checks would fail if the empty line was encountered prematurely, and consequently we can get away with the current string comparisons even with non-NUL-terminated buffers are passed to fsck_object().

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 fsck.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/fsck.c b/fsck.c
index dd77628..db6aaa4 100644
--- a/fsck.c
+++ b/fsck.c
@@ -237,6 +237,26 @@ static int fsck_tree(struct tree *item, int strict, fsck_error error_func)
 	return retval;
 }
 
+static int must_have_empty_line(const void *data, unsigned long size,
+	struct object *obj, fsck_error error_func)
+{
+	const char *buffer = (const char *)data;
+	int i;
+
+	for (i = 0; i < size; i++) {
+		switch (buffer[i]) {
+		case '\0':
+			return error_func(obj, FSCK_ERROR,
+				"invalid message: NUL at offset %d", i);
+		case '\n':
+			if (i + 1 < size && buffer[i + 1] == '\n')
+				return 0;
+		}
+	}
+
+	return error_func(obj, FSCK_ERROR, "invalid buffer: missing empty line");
+}
+
 static int fsck_ident(const char **ident, struct object *obj, fsck_error error_func)
 {
 	char *end;
@@ -284,6 +304,9 @@ static int fsck_commit_buffer(struct commit *commit, const char *buffer,
 	unsigned parent_count, parent_line_count = 0;
 	int err;
 
+	if (must_have_empty_line(buffer, size, &commit->object, error_func))
+		return -1;
+
 	if (!skip_prefix(buffer, "tree ", &buffer))
 		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'tree' line");
 	if (get_sha1_hex(buffer, tree_sha1) || buffer[40] != '\n')

-- 
2.0.0.rc3.9669.g840d1f9