From fc2dcd4fca6186e98567c29d8467b72a42fd7fd4 Mon Sep 17 00:00:00 2001
From: Cayce <cayce@cayce-co.xyz>
Date: Wed, 28 Oct 2026 21:01:44 +0000
Subject: [PATCH] =?UTF-8?q?backup:=20backup-pull=20user=20=E2=80=94=20read?=
 =?UTF-8?q?-only=20rsync-only=20SSH=20access=20(Tanda=20B,=20point=202)?=
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System user backup-pull created on the VPS (no sudo, locked password).
authorized_keys restricted with restrict + forced command
rrsync -ro /var/backups/cayce. Verified with a since-deleted throwaway
key: no shell, no arbitrary commands, no sftp/scp, no reads outside
/var/backups/cayce, no writes; the positive rsync pull works.

authorized_keys is left EMPTY — the operator adds their real key with
the exact line documented in deploy/backup/backup-pull-setup.md.
---
 deploy/backup/backup-pull-setup.md | 43 ++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 deploy/backup/backup-pull-setup.md

diff --git a/deploy/backup/backup-pull-setup.md b/deploy/backup/backup-pull-setup.md
new file mode 100644
index 0000000..f725136
--- /dev/null
+++ b/deploy/backup/backup-pull-setup.md
@@ -0,0 +1,43 @@
+# backup-pull — usuario de solo lectura para el pull desde la Mac
+
+La VPS genera los backups cifrados en `/var/backups/cayce/YYYY-MM-DD/`.
+La Mac los descarga por rsync con una clave SSH **restringida**. La VPS
+nunca tiene credenciales para escribir ni borrar nada fuera de sí misma.
+
+## Estado instalado en la VPS
+
+- Usuario de sistema `backup-pull` (uid 1001): **sin sudo**, password
+  bloqueado, home `/home/backup-pull`, shell `/bin/sh` (necesario para que
+  sshd ejecute el forced command; la restricción real la pone la clave, no
+  el shell).
+- `/home/backup-pull/.ssh/authorized_keys` (600, backup-pull:backup-pull) —
+  **vacío** hasta que el operador añada su clave pública.
+- `/var/backups/cayce` → `root:backup-pull`, `750`; artefactos `640`.
+
+## Formato de la línea authorized_keys (una sola línea)
+
+    restrict,command="/usr/bin/rrsync -ro /var/backups/cayce" ssh-ed25519 AAAA... comentario
+
+`restrict` = no-pty, no-port-forwarding, no-agent-forwarding, no-X11-forwarding
+(y sin sftp). `rrsync -ro` = solo rsync de LECTURA, confinado a
+`/var/backups/cayce`. Añadirla con:
+
+    echo 'restrict,command="/usr/bin/rrsync -ro /var/backups/cayce" ssh-ed25519 AAAA... cayce-mac-pull' \
+      | sudo tee -a /home/backup-pull/.ssh/authorized_keys
+
+## Pull desde la Mac
+
+    rsync -av --partial backup-pull@15.235.3.239:/ ~/backups/cayce/
+
+## Verificación realizada (2026-10-28, con clave desechada después)
+
+| Prueba | Resultado |
+|---|---|
+| Shell interactivo | ✗ `rrsync error: Not invoked via sshd` |
+| Comando arbitrario (`cat /etc/shadow`) | ✗ `SSH_ORIGINAL_COMMAND does not run rsync` |
+| rsync de `/etc/` | ✗ `invalid rsync-command syntax or options` (fuera del root permitido) |
+| scp/sftp | ✗ (restrict) |
+| **rsync pull de `/var/backups/cayce/`** | ✓ funciona |
+| rsync write (upload) | ✗ protocolo cortado, nada escrito |
+
+La clave usada para las pruebas se **borró**; `authorized_keys` quedó vacío.