[PATCH 1/2] procd: mount /dev with noexec
Rui Salvaterra
rsalvaterra at gmail.com
Sun Jan 9 15:27:27 PST 2022
/dev is writable. Allowing execution inside it makes it a possible attack
vector. Kees Cook recently sent a kernel patch [1] in order to mount /dev as
noexec and nosuid for systems which rely on CONFIG_DEVTMPFS_MOUNT=y to
create/populate /dev, which isn't our case (it's procd's responsibility).
Add noexec to the /dev mount flags, since we already use nosuid (and keep the
coldplug flags symmetric, while at it). This carries the risk of breaking very
old, pre-KMS graphics drivers [2], but it shouldn't be a problem for systems
built in the last ~15 years. The vast majority of our targets doesn't have a
GPU, anyway. :)
[1] https://lore.kernel.org/all/YcMfDOyrg647RCmd@debian-BULLSEYE-live-builder-AMD64/
[2] https://lore.kernel.org/all/CAPXgP12e5LpN6XVxaXOHhH=u8XXN==2reTaJDCoCk4tP4QduDQ@mail.gmail.com/
Signed-off-by: Rui Salvaterra <rsalvaterra at gmail.com>
---
initd/early.c | 2 +-
plug/coldplug.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/initd/early.c b/initd/early.c
index d69495e..87fee65 100644
--- a/initd/early.c
+++ b/initd/early.c
@@ -61,7 +61,7 @@ early_mounts(void)
mount("proc", "/proc", "proc", MS_NOATIME | MS_NODEV | MS_NOEXEC | MS_NOSUID, 0);
mount("sysfs", "/sys", "sysfs", MS_NOATIME | MS_NODEV | MS_NOEXEC | MS_NOSUID, 0);
mount("cgroup2", "/sys/fs/cgroup", "cgroup2", MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RELATIME, "nsdelegate");
- mount("tmpfs", "/dev", "tmpfs", MS_NOATIME | MS_NOSUID, "mode=0755,size=512K");
+ mount("tmpfs", "/dev", "tmpfs", MS_NOATIME | MS_NOEXEC | MS_NOSUID, "mode=0755,size=512K");
ignore(symlink("/tmp/shm", "/dev/shm"));
mkdir("/dev/pts", 0755);
mount("devpts", "/dev/pts", "devpts", MS_NOATIME | MS_NOEXEC | MS_NOSUID, "mode=600");
diff --git a/plug/coldplug.c b/plug/coldplug.c
index b185083..b9462e7 100644
--- a/plug/coldplug.c
+++ b/plug/coldplug.c
@@ -48,7 +48,7 @@ void procd_coldplug(void)
if (!is_container()) {
umount2("/dev/pts", MNT_DETACH);
umount2("/dev/", MNT_DETACH);
- mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755,size=512K");
+ mount("tmpfs", "/dev", "tmpfs", MS_NOATIME | MS_NOEXEC | MS_NOSUID, "mode=0755,size=512K");
mkdir("/dev/pts", 0755);
mount("devpts", "/dev/pts", "devpts", MS_NOEXEC | MS_NOSUID, 0);
}
--
2.34.1
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