Be more careful with user-supplied buffersrb/fix-2333

This adds in missing calls to `git_buf_sanitize` and fixes a
number of places where `git_buf` APIs could inadvertently write
NUL terminator bytes into invalid buffers.  This also changes the
behavior of `git_buf_sanitize` to NUL terminate a buffer if it can
and of `git_buf_shorten` to do nothing if it can.

Adds tests of filtering code with zeroed (i.e. unsanitized) buffer
which was previously triggering a segfault.

1 files changed, 10 insertions, 3 deletions

diff --git a/tests/object/blob/filter.c b/tests/object/blob/filter.c
index 0b2d6bf9e..3cc8fdc3d 100644
--- a/tests/object/blob/filter.c
+++ b/tests/object/blob/filter.c
@@ -112,7 +112,7 @@ void test_object_blob_filter__to_odb(void)
 	git_config *cfg;
 	int i;
 	git_blob *blob;
-	git_buf out = GIT_BUF_INIT;
+	git_buf out = GIT_BUF_INIT, zeroed;
 
 	cl_git_pass(git_repository_config(&cfg, g_repo));
 	cl_assert(cfg);
@@ -127,13 +127,20 @@ void test_object_blob_filter__to_odb(void)
 	for (i = 0; i < CRLF_NUM_TEST_OBJECTS; i++) {
 		cl_git_pass(git_blob_lookup(&blob, g_repo, &g_crlf_oids[i]));
 
+		/* try once with allocated blob */
 		cl_git_pass(git_filter_list_apply_to_blob(&out, fl, blob));
-
 		cl_assert_equal_sz(g_crlf_filtered[i].size, out.size);
-
 		cl_assert_equal_i(
 			0, memcmp(out.ptr, g_crlf_filtered[i].ptr, out.size));
 
+		/* try again with zeroed blob */
+		memset(&zeroed, 0, sizeof(zeroed));
+		cl_git_pass(git_filter_list_apply_to_blob(&zeroed, fl, blob));
+		cl_assert_equal_sz(g_crlf_filtered[i].size, zeroed.size);
+		cl_assert_equal_i(
+			0, memcmp(zeroed.ptr, g_crlf_filtered[i].ptr, zeroed.size));
+		git_buf_free(&zeroed);
+
 		git_blob_free(blob);
 	}