commit-graph.c: remove path normalization, comparison

As of the previous patch, all calls to 'commit-graph.c' functions which
perform path normalization (for e.g., 'get_commit_graph_filename()') are
of the form 'ctx->odb->path', which is always in normalized form.

Now that there are no callers passing non-normalized paths to these
functions, ensure that future callers are bound by the same restrictions
by making these functions take a 'struct object_directory *' instead of
a 'const char *'. To match, replace all calls with arguments of the form
'ctx->odb->path' with 'ctx->odb' To recover the path, functions that
perform path manipulation simply use 'odb->path'.

Further, avoid string comparisons with arguments of the form
'odb->path', and instead prefer raw pointer comparisons, which
accomplish the same effect, but are far less brittle.

This has a pleasant side-effect of making these functions much more
robust to paths that cannot be normalized by 'normalize_path_copy()',
i.e., because they are outside of the current working directory.

For example, prior to this patch, Valgrind reports that the following
uninitialized memory read [1]:

  $ ( cd t && GIT_DIR=../.git valgrind git rev-parse HEAD^ )

because 'normalize_path_copy()' can't normalize '../.git' (since it's
relative to but above of the current working directory) [2].

By using a 'struct object_directory *' directly,
'get_commit_graph_filename()' does not need to normalize, because all
paths are relative to the current working directory since they are
always read from the '->path' of an object directory.

[1]: https://lore.kernel.org/git/20191027042116.GA5801@sigill.intra.peff.net.
[2]: The bug here is that 'get_commit_graph_filename()' returns the
     result of 'normalize_path_copy()' without checking the return
     value.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/t/helper/test-read-graph.c b/t/helper/test-read-graph.c
index d2884efe0a..2c2f65f06c 100644
--- a/t/helper/test-read-graph.c
+++ b/t/helper/test-read-graph.c
@@ -11,12 +11,12 @@ int cmd__read_graph(int argc, const char **argv)
 	int open_ok;
 	int fd;
 	struct stat st;
-	const char *object_dir;
+	struct object_directory *odb;
 
 	setup_git_directory();
-	object_dir = get_object_directory();
+	odb = the_repository->objects->odb;
 
-	graph_name = get_commit_graph_filename(object_dir);
+	graph_name = get_commit_graph_filename(odb);
 
 	open_ok = open_commit_graph(graph_name, &fd, &st);
 	if (!open_ok)