upload-pack: read uploadpack.lazyFetchTrusted

Previous commits created and prepared the path_allowlist_apply()
and path_allowlist_config_apply() functions, but used them only for the
"safe.directory" configuration variable.

Let's reuse these functions for a new "uploadpack.lazyFetchTrusted"
configuration variable.

It allows us to:

  - read an allowlist from that config variable,
  - check if the current repo is in that list, and
  - return the result from a new upload_pack_lazy_fetch_trusted()
    function.

As path_allowlist_config_apply() lets each caller decide which paths
it is willing to accept using a callback, let's pass it a new
allow_trusted_path() callback. Unlike the "safe.directory" callback, it
accepts only absolute paths, and not ".", as `upload-pack` always
serves a repository given by an absolute path, so there is no "current
repository" for "." to refer to.

Note that a served repository is identified by its git directory, and
not by its worktree. This is because `upload-pack` uses enter_repo()
instead of the usual repository discovery, so it never learns about a
worktree and `r->worktree` is always NULL there. In practice this
means that a non-bare repository served as "/srv/repo" has to be
allowlisted as "/srv/repo/.git".

The new upload_pack_lazy_fetch_trusted() function will be used in a
following commit.

Note that the new config variable should be read only from protected
configuration files.

Signed-off-by: Christian Couder <christian.couder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

upload-pack.c

@@ -34,6 +34,8 @@
 #include "json-writer.h"
 #include "strmap.h"
 #include "promisor-remote.h"
+#include "setup.h"
+#include "abspath.h"
 
 /* Remember to update object flag allocation in object.h */
 #define THEY_HAVE	(1u << 11)
@@ -1343,6 +1345,63 @@ static int upload_pack_config(const char *var, const char *value,
 	return parse_hide_refs_config(var, value, "uploadpack", &data->hidden_refs);
 }
 
+/*
+ * Only absolute paths make sense here. Unlike 'safe.directory', "."
+ * is not accepted, as the served repository is always identified by
+ * an absolute path.
+ */
+static bool allow_trusted_path(const char *path, void *cbdata_)
+{
+	struct path_allowlist_cb_data *cbdata = cbdata_;
+
+	if (is_absolute_path(path))
+		return true;
+
+	warning(_("%s '%s' not absolute"), cbdata->key, path);
+	return false;
+}
+
+struct lazy_fetch_trusted {
+	char *repo_path;
+	bool trusted;
+};
+
+static int upload_pack_protected_lazy_fetch_config(const char *var, const char *value,
+						   const struct config_context *ctx UNUSED,
+						   void *cb_data)
+{
+	struct lazy_fetch_trusted *data = cb_data;
+	struct path_allowlist_cb_data cbdata = { .key = var };
+
+	if (strcmp("uploadpack.lazyfetchtrusted", var))
+		return 0;
+
+	path_allowlist_config_apply(var, value, data->repo_path, &data->trusted,
+				    allow_trusted_path, &cbdata);
+
+	return 0;
+}
+
+bool upload_pack_lazy_fetch_trusted(struct repository *r)
+{
+	struct lazy_fetch_trusted data = { 0 };
+
+	/*
+	 * A served repository is identified by its git directory, as
+	 * `upload-pack` uses enter_repo() instead of the usual repository
+	 * discovery, so its worktree, if any, is never known here.
+	 */
+	data.repo_path = real_pathdup(r->gitdir, 0);
+	if (!data.repo_path)
+		return false;
+
+	git_protected_config(upload_pack_protected_lazy_fetch_config, &data);
+
+	free(data.repo_path);
+
+	return !!data.trusted;
+}
+
 static int upload_pack_protected_config(const char *var, const char *value,
 					const struct config_context *ctx UNUSED,
 					void *cb_data)

upload-pack.h

@@ -12,4 +12,7 @@ struct strbuf;
 int upload_pack_advertise(struct repository *r,
 			  struct strbuf *value);
 
+/* Is this repo trusted for lazy fetching? */
+bool upload_pack_lazy_fetch_trusted(struct repository *r);
+
 #endif /* UPLOAD_PACK_H */