[PATCH 2/3] Add /dev/fd and /dev/std*

Demi Marie Obenour
2025-09-15T00:20:39Z

This is nearly same as 14483e1a690c (img/app: add /dev/fd and /dev/std*),
but for the host and for vm/sys/net. The only difference is that the
symlinks are created in init, rather than in rc.init. This ensures that
nothing in the main system can run before they the links are created.

While only Spectrum-provided code should run in these VMs, third-party
dependencies are likely to only be tested in an environment where these
links are present. Since the BSDs also have these links, some code
might even use them on purpose.

Not having these links could cause severe bugs. For instance, if
/dev/stdout or /dev/stderr is missing, writing to them will create a
regular file instead. This could cause other code to misbehave.
Furthermore, /dev is a devtmpfs, so this could consume a lot of memory.

In the host, the links are added in the main system, rather than in the
initramfs. This is per Alyssa's suggestion in [1].

[1]: https://spectrum-os.org/lists/archives/spectrum-devel/87h5xdjo9p.fsf@alyssa.is/

Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
---
host/rootfs/etc/init | 8 ++++++++
vm/sys/net/etc/init | 8 ++++++++
2 files changed, 16 insertions(+)

diff --git a/host/rootfs/etc/init b/host/rootfs/etc/init
index 4085fa55545e7309004967e443e47fc2b82b0663..b6e6122ddb987a5463c0924cd56e1a26cf5bfd98 100755
--- a/host/rootfs/etc/init
+++ b/host/rootfs/etc/init
@@ -1,5 +1,13 @@
#!/bin/execlineb -s0
# SPDX-License-Identifier: EUPL-1.2+
# SPDX-FileCopyrightText: 2022 Alyssa Ross <hi@alyssa.is>
+# Symlink creation (if it's copyrightable):
+# SPDX-License-Identifier: CC0-1.0
+# SPDX-FileCopyrightText: 2025 Demi Marie Obenour <demiobenour@gmail.com>
+
+/usr/bin/if { /usr/bin/ln -s /proc/self/fd /dev }
+/usr/bin/if { /usr/bin/ln -s /proc/self/fd/0 /dev/stdin }
+/usr/bin/if { /usr/bin/ln -s /proc/self/fd/1 /dev/stdout }
+/usr/bin/if { /usr/bin/ln -s /proc/self/fd/2 /dev/stderr }

/bin/s6-linux-init -c /etc/s6-linux-init -s /run/param -- $@
diff --git a/vm/sys/net/etc/init b/vm/sys/net/etc/init
index 6424e221e0fb929e107271bd52b61706b9f1855e..de409e9296a24d42cef50605496efc520790559e 100755
--- a/vm/sys/net/etc/init
+++ b/vm/sys/net/etc/init
@@ -1,5 +1,13 @@
#!/bin/execlineb -s0
# SPDX-License-Identifier: EUPL-1.2+
# SPDX-FileCopyrightText: 2022 Alyssa Ross <hi@alyssa.is>
+# Symlink creation (if it's copyrightable):
+# SPDX-License-Identifier: CC0-1.0
+# SPDX-FileCopyrightText: 2025 Demi Marie Obenour <demiobenour@gmail.com>
+
+/usr/bin/if { /usr/bin/ln -s /proc/self/fd /dev }
+/usr/bin/if { /usr/bin/ln -s /proc/self/fd/0 /dev/stdin }
+/usr/bin/if { /usr/bin/ln -s /proc/self/fd/1 /dev/stdout }
+/usr/bin/if { /usr/bin/ln -s /proc/self/fd/2 /dev/stderr }

/bin/s6-linux-init -Bc /etc/s6-linux-init -- $@

--
2.51.0