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Make rootless privileged containers share the same tty devices as rootfull ones

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Until Podman v4.3, privileged rootfull containers would expose all the
host devices to the container while rootless ones would exclude
`/dev/ptmx` and `/dev/tty*`.

When 5a2405ae1b ("Don't mount /dev/tty* inside privileged containers
running systemd") landed, rootfull containers started excluding all the
`/dev/tty*` devices when the container would be running in systemd
mode, reducing the disparity between rootless and rootfull containers
when running in this mode.

However, this commit regressed some legitimate use cases: exposing
non-virtual-terminal tty devices (modems, arduinos, serial
consoles, ...) to the container, and the regression was addressed in
f4c81b0aa5 ("Only prevent VTs to be mounted inside privileged
systemd containers").

This now calls into question why all tty devices were historically
prevented from being shared to the rootless non-privileged containers.
A look at the podman git history reveals that the code was introduced
as part of ba430bfe5e ("podman v2 remove bloat v2"), and obviously
was copy-pasted from some other code I couldn't find.

In any case, we can easily guess that this check was put for the same
reason 5a2405ae1b was introduced: to prevent breaking the host
environment's consoles. This also means that excluding *all* tty
devices is overbearing, and should instead be limited to just virtual
terminals like we do on the rootfull path.

This is what this commit does, thus making the rootless codepath behave
like the rootfull one when in systemd mode.

This leaves `/dev/ptmx` as the main difference between the two
codepath. Based on the blog post from the then-runC maintainer[1] and
this Red Hat bug[2], I believe that this is intentional and a needed
difference for the rootless path.

Closes: #16925
Suggested-by: Fabian Holler <mail@fholler.de>
Signed-off-by: Martin Roukala (né Peres) <martin.roukala@mupuf.org>

[1]: https://www.cyphar.com/blog/post/20160627-rootless-containers-with-runc
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=501718
This commit is contained in:
Martin Roukala (né Peres) 2023-01-16 12:04:58 +02:00
parent d558a792f4
commit 70057c8b47
No known key found for this signature in database
2 changed files with 44 additions and 5 deletions
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24
pkg/util/utils_linux.go
View file

@ -7,7 +7,6 @@ import (
"os"
"path"
"path/filepath"
"strings"
"syscall"
"github.com/containers/podman/v4/libpod/define"
@ -107,7 +106,18 @@ func AddPrivilegedDevices(g *generate.Generator, systemdMode bool) error {
Source: d.Path,
Options: []string{"slave", "nosuid", "noexec", "rw", "rbind"},
}
if d.Path == "/dev/ptmx" || strings.HasPrefix(d.Path, "/dev/tty") {
/* The following devices should not be mounted in rootless containers:
*
* /dev/ptmx: The host-provided /dev/ptmx should not be shared to
* the rootless containers for security reasons, and
* the container runtime will create it for us
* anyway (ln -s /dev/pts/ptmx /dev/ptmx);
* /dev/tty[0-9]+: Prevent the container from taking over the host's
* virtual consoles, even when not in systemd mode
* for backwards compatibility.
*/
if d.Path == "/dev/ptmx" || isVirtualConsoleDevice(d.Path) {
continue
}
if _, found := mounts[d.Path]; found {
@ -121,6 +131,16 @@ func AddPrivilegedDevices(g *generate.Generator, systemdMode bool) error {
}
} else {
for _, d := range hostDevices {
/* Restrict access to the virtual consoles *only* when running
* in systemd mode to improve backwards compatibility. See
* https://github.com/containers/podman/issues/15878.
*
* NOTE: May need revisiting in the future to drop the systemd
* condition if more use cases end up breaking the virtual terminals
* of people who specifically disable the systemd mode. It would
* also provide a more consistent behaviour between rootless and
* rootfull containers.
*/
if systemdMode && isVirtualConsoleDevice(d.Path) {
continue
}

25
test/system/030-run.bats
View file

@ -952,10 +952,29 @@ $IMAGE--c_ok" \
run_podman stop -t 0 $cid
}
# 16925: --privileged + --systemd = share non-virtual-terminal TTYs
@test "podman run --privileged as root with systemd mounts non-vt /dev/tty devices" {
skip_if_rootless "this test only makes sense as root"
@test "podman run --privileged as rootless will not mount /dev/tty\d+" {
skip_if_not_rootless "this test as rootless"
# First, confirm that we _have_ /dev/ttyNN devices on the host.
# ('skip' would be nicer in some sense... but could hide a regression.
# Fedora, RHEL, Debian, Ubuntu, Gentoo, all have /dev/ttyN, so if
# this ever triggers, it means a real problem we should know about.)
vt_tty_devices_count=$(find /dev -regex '/dev/tty[0-9].*' | wc -w)
assert "$vt_tty_devices_count" != "0" \
"Expected at least one /dev/ttyN device on host"
run_podman run --rm -d --privileged $IMAGE ./pause
cid="$output"
run_podman exec $cid sh -c "find /dev -regex '/dev/tty[0-9].*' | wc -w"
assert "$output" = "0" \
"ls /dev/tty[0-9]: should have no ttyN devices"
run_podman stop -t 0 $cid
}
# 16925: --privileged + --systemd = share non-virtual-terminal TTYs (both rootful and rootless)
@test "podman run --privileged as root with systemd mounts non-vt /dev/tty devices" {
# First, confirm that we _have_ non-virtual terminal /dev/tty* devices on
# the host.
non_vt_tty_devices_count=$(find /dev -regex '/dev/tty[^0-9].*' | wc -w)