From a10f52a7565c549612c92b8e736a6698a53db330 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Wed, 1 Sep 2021 11:59:00 +0100
Subject: [PATCH] run: Block clone3() in sandbox

clone3() can be used to implement clone() with CLONE_NEWUSER, allowing
a sandboxed process to get CAP_SYS_ADMIN in a new namespace and
manipulate its root directory. We need to block this so that AF_UNIX-based
socket servers (X11, Wayland, etc.) can rely on
/proc/PID/root/.flatpak-info existing for all Flatpak-sandboxed apps.

Partially fixes GHSA-67h7-w3jq-vh4q.

Thanks: an anonymous reporter
Signed-off-by: Simon McVittie <smcv@collabora.com>

Conflict:NA
Reference:https://github.com/flatpak/flatpak/commit/a10f52a7565c549612c92b8e736a6698a53db330

---
 common/flatpak-run.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/common/flatpak-run.c b/common/flatpak-run.c
index 5cf6d2e..dad0cfe 100644
--- a/common/flatpak-run.c
+++ b/common/flatpak-run.c
@@ -2832,6 +2832,12 @@ setup_seccomp (FlatpakBwrap   *bwrap,
 
     /* Don't allow faking input to the controlling tty (CVE-2017-5226) */
     {SCMP_SYS (ioctl), EPERM, &SCMP_A1 (SCMP_CMP_MASKED_EQ, 0xFFFFFFFFu, (int) TIOCSTI)},
+
+    /* seccomp can't look into clone3()'s struct clone_args to check whether
+     * the flags are OK, so we have no choice but to block clone3().
+     * Return ENOSYS so user-space will fall back to clone().
+     * (GHSA-67h7-w3jq-vh4q; see also https://github.com/moby/moby/commit/9f6b562d) */
+    {SCMP_SYS (clone3), ENOSYS},
   };
 
   struct
-- 
2.27.0