fix: Various security fixes (#38103) (#38151)

Backport #38103

- Enforce org visibility on organization label read endpoints (private
org labels no longer leak to non-members).
- Block fork sync (`merge-upstream`) when the base repo is no longer
readable (stops pulling commits after a parent goes private).
- Remove `REVERSE_PROXY_LIMIT` / `REVERSE_PROXY_TRUSTED_PROXIES` from
the Docker `app.ini` templates (the `= *` default allowed
`X-WEBAUTH-USER` impersonation; reverse-proxy auth is now opt-in and
admin-configured).
- Enforce single-use TOTP passcodes across web login, password-reset,
and Basic-Auth `X-Gitea-OTP` (fixes a TOCTOU race and a stateless
replay).
- Re-check branch write permission for every ref in a push (the
pre-receive hook cached the first ref's result, letting a per-branch
maintainer-edit grant escalate to full repo write).

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/repository/merge_upstream.go

@@ -8,7 +8,9 @@ import (
 	"fmt"
 
 	issue_model "code.gitea.io/gitea/models/issues"
+	access_model "code.gitea.io/gitea/models/perm/access"
 	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unit"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/gitrepo"
@@ -26,6 +28,17 @@ func MergeUpstream(ctx reqctx.RequestContext, doer *user_model.User, repo *repo_
 	if err = repo.GetBaseRepo(ctx); err != nil {
 		return "", err
 	}
+
+	// The doer must still be able to read the base repository's code. Otherwise a fork created
+	// while the base repo was public could keep pulling commits after it turned private.
+	basePerm, err := access_model.GetDoerRepoPermission(ctx, repo.BaseRepo, doer)
+	if err != nil {
+		return "", err
+	}
+	if !basePerm.CanRead(unit.TypeCode) {
+		return "", util.NewPermissionDeniedErrorf("permission denied to read base repo %d", repo.BaseRepo.ID)
+	}
+
 	divergingInfo, err := GetUpstreamDivergingInfo(ctx, repo, branch)
 	if err != nil {
 		return "", err