pkg/subscriptions: Modernize FIPS mounts #2174

neverpanic · 2024-09-25T12:00:32Z

/etc/system-fips is deprecated in CentOS Stream 9 and has been removed from CentOS Stream 10. UBI8 containers still contain /etc/system-fips -> /run/secrets/system-fips, but UBI9 containers do not, so creating /run/secrets/system-fips on UBI9 (or later) does not serve a useful purpose. See [1, 2].

Instead of checking /etc/system-fips to determine whether FIPS mode is enabled on the host, read /proc/sys/crypto/fips_enabled, which works for all supported RHEL versions and likely even earlier.

In CentOS 10 Stream, the crypto-policies package does now contain /usr/share/crypto-policies/default-fips-config, which is meant to serve as a file to bind-mount over /etc/crypto-policies/config when in FIPS mode [3]. Manual creation of this file is thus no longer required in containers/common for modern containers. Using this file as a source also enables improvements in crypto-policies tooling which will now

unmount the two bind mounts when a user manually changes the policy using update-crypto-policies --set, something which was previously broken in containers because /etc/crypto-policies/config was a read-only bind-mount, and
unmount and restore the two bind-mounts when the crypto-policies package is updated. The crypto-policies package will only do these steps if the the bind mounts for crypto-policies use the
/usr/share/crypto-policies/default-fips-config
file as source, so it makes sense for containers/common to switch to that.

Closes: #2130
Related: https://issues.redhat.com/browse/CRYPTO-13556

Honny1

Thanks!

The approach looks good overall, but I have a few suggestions that should reduce maintenance costs. Also, vendoring will need to be done to the projects that using c/common for example podman and buildah to make the changes take effect.

PTAL @mtrmac, @Luap99

pkg/subscriptions/subscriptions.go

mtrmac · 2024-10-01T14:33:34Z

pkg/subscriptions/subscriptions.go

+				logrus.Errorf("Adding FIPS mode bind mounts to container: %v", err)
+			}
+		} else {
+			logrus.Debug("/proc/sys/crypto/fips_enabled does not contain '1', not adding FIPS mode bind mounts")


Is it worth logging the value here?

I don't think so. The value can't change without a reboot, and it's going to be the the same across the entire host, regardless of whether one is inside of a container or outside. It should be simple to obtain the actual value using cat if necessary for debugging.

The only case where this could differ from the global value is if somebody bind-mounted a file over it for testing purposes. I don't think we need to handle this eventuality.

mtrmac · 2024-10-01T14:42:40Z

pkg/subscriptions/subscriptions.go

-		file, err := os.Create(fipsFile)
+	fipsFileHost := filepath.Join(mountPoint, "etc/system-fips")
+	if fileutils.Lexists(fipsFileHost) != nil {
+		fipsFileTarget, err := filepath.EvalSymlinks(fipsFileHost)


This conceptually allows an attacker to set up /etc/system-fips inside the container to be a symlink with ../../… to break out of the container and refer to hosts’ files.

Yes, we actually only compare the fipsFileTarget text without referring to the possibly-unwanted file, but, still…

In other words, either we care about the specific symlink text, and we can just Readlink (probably not), or we care about where the symlink evaluates, whatever its form, and in that case .. in the / directory of the container should be evaluated correctly (restricted to the containers’ root).

(https://github.com/cyphar/filepath-securejoin is used for that purpose in some parts of the codebase.)

Good catch, fixed by using securejoin. I still need a fileutils.Lexists, because the log messages should probably differ between /etc/system-fips not existing (which is a common config) and /etc/system-fips existing but not pointing to /run/secrets/system-fips (which is probably an uncommon config). That shouldn't be an issue, though, since fileutils.Lexists doesn't follow symlinks.

pkg/subscriptions/subscriptions.go

mtrmac

I didn’t actually review the substance of the PR, whether the code correctly handles all relevant versions of the OSes and behaviors.

Just looking at the mechanism, all the filepath.Join(mountPoint, …) in this file make me worried about symlink breakouts. There might not be much actually wrong there (at worst, I guess, triggering an an audit message about a DAC or SELinux permission violation by the container runtime when checking for presence of an out-of-contaienr file), but that’s just one small refactor away from disaster.

I do appreciate that almost all of that is pre-existing and not directly relevant to this PR.

Luap99 · 2024-10-01T15:56:52Z

Just looking at the mechanism, all the filepath.Join(mountPoint, …) in this file make me worried about symlink breakouts. There might not be much actually wrong there (at worst, I guess, triggering an an audit message about a DAC or SELinux permission violation by the container runtime when checking for presence of an out-of-contaienr file), but that’s just one small refactor away from disaster.

I do appreciate that almost all of that is pre-existing and not directly relevant to this PR.

I noticed this last week when I looked at this PR and reported this internally so yes this is an pre existing issue, fix in #2185
@neverpanic once this is merged please rebase and make sure all joins with of the container mount point use securejoin.

neverpanic · 2024-10-06T08:53:49Z

I'm on PTO until Oct 14, I'll fix the comments after that.

pkg/subscriptions/subscriptions.go

Luap99 · 2024-10-22T17:16:25Z

pkg/subscriptions/subscriptions.go

+	fips_enabled, err := os.ReadFile("/proc/sys/crypto/fips_enabled")
+	if err != nil {
+		logrus.Errorf("Failed to read /proc/sys/crypto/fips_enabled to determine FIPS state: %v", err)
+		return false
+	}


This will log an error when the file does not exists, it not clear to me does the kernel always has the file or is that set to some CONFIG_ options in the kernel. If so we should certainly ignore ENOENT?

Second, this logs an error and then assumes fips is disabled, Given this is a security option should we not outright fail with the error (e.g. return the error to the caller)? I do realize MountsWithUIDGID() does not return an error so we would need to add a new function so maybe it is not worth it. Maybe it is not important enough but I always very much find it odd to log an error but then start the container anyway. Either way the issue is pre existing so I would not block this on it.

The kernel always has that file, so there's no need to ignore ENOENT.

I can make the change to bubble up the error, but as you said, it's going to be a larger change because MountsWithUIDGID() does not currently fail. Maybe we should do that in a separate PR afterwards?

The kernel always has that file, so there's no need to ignore ENOENT.

@neverpanic not always. I work with systems where CONFIG_CRYPTO_FIPS is not always enabled.

Should be fixed now.

pkg/subscriptions/subscriptions.go

Luap99

one small nit otherwise LGTM

cc @TomSweeneyRedHat not sure if the fips changes here need any updates in the container RHEL docs.

Luap99 · 2024-10-30T17:24:05Z

pkg/subscriptions/subscriptions.go

+func shouldAddFIPSMounts() bool {
+	fips_enabled, err := os.ReadFile("/proc/sys/crypto/fips_enabled")
+	if err != nil {
+		if !os.IsNotExist(err) {


new code should use errors.Is(err, fs.ErrNotExist)

I've used os.ErrNotExist, since that was already imported.

/etc/system-fips is deprecated in CentOS Stream 9 and has been removed from CentOS Stream 10. UBI8 containers still contain /etc/system-fips -> /run/secrets/system-fips, but UBI9 containers do not, so creating /run/secrets/system-fips on UBI9 (or later) does not serve a useful purpose. See [1, 2]. Instead of checking /etc/system-fips to determine whether FIPS mode is enabled on the host, read /proc/sys/crypto/fips_enabled, which works for all supported RHEL versions and likely even earlier. In CentOS 10 Stream, the crypto-policies package does now contain /usr/share/crypto-policies/default-fips-config, which is meant to serve as a file to bind-mount over /etc/crypto-policies/config when in FIPS mode [3]. Manual creation of this file is thus no longer required in containers/common for modern containers. Using this file as a source also enables improvements in crypto-policies tooling which will now - unmount the two bind mounts when a user manually changes the policy using update-crypto-policies --set, something which was previously broken in containers because /etc/crypto-policies/config was a read-only bind-mount, and - unmount and restore the two bind-mounts when the crypto-policies package is updated. The crypto-policies package will only do these steps if the the bind mounts for crypto-policies use the /usr/share/crypto-policies/default-fips-config file as source, so it makes sense for containers/common to switch to that. [1]: https://gitlab.com/redhat-crypto/fedora-crypto-policies/-/merge_requests/111 [2]: https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html/9.0_release_notes/deprecated_functionality#deprecated-functionality_security [3]: https://gitlab.com/redhat-crypto/fedora-crypto-policies/-/commit/04ceadccfc07e5946b08157d06ca5c0d5a229d92 Closes: containers#2130 Related: https://issues.redhat.com/browse/CRYPTO-13556 Signed-off-by: Clemens Lang <[email protected]>

Luap99

LGTM

kwilczynski · 2024-11-01T09:44:06Z

Nice!

kwilczynski · 2024-11-01T09:44:12Z

/approve
/lgtm

openshift-ci · 2024-11-01T09:44:15Z

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In response to this:

/approve
/lgtm

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Luap99 · 2024-11-07T11:04:59Z

@mtrmac Mind giving this a final review/merge? I think it would be good to get this into podman 5.3.

giuseppe

/lgtm

openshift-ci · 2024-11-07T11:14:22Z

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Honny1 suggested changes Oct 1, 2024

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