core: imply DeviceAllow=/dev/tpmrm0 with LoadCredentialEncrypted

If the device access policy is restricted, add implicitly access to the TPM
if at least one encrypted credential needs to be loaded.

Fixes https://github.com/systemd/systemd/issues/26042

diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
index b6e71cce2ba51754a9f8190f01261e8ea05b269d..bad21ceb0c2bc7792e542a3f100a80a9fc47b526 100644 (file)
--- a/man/systemd.exec.xml
+++ b/man/systemd.exec.xml
@@ -3154,7 +3154,13 @@ StandardInputData=V2XigLJyZSBubyBzdHJhbmdlcnMgdG8gbG92ZQpZb3Uga25vdyB0aGUgcnVsZX
         authenticated credentials improves security as credentials are not stored in plaintext and only
         authenticated and decrypted into plaintext the moment a service requiring them is started. Moreover,
         credentials may be bound to the local hardware and installations, so that they cannot easily be
-        analyzed offline, or be generated externally.</para>
+        analyzed offline, or be generated externally. When <varname>DevicePolicy=</varname> is set to
+        <literal>closed</literal> or <literal>strict</literal>, or set to <literal>auto</literal> and
+        <varname>DeviceAllow=</varname> is set, or <varname>PrivateDevices=</varname> is set, then this
+        setting adds <filename>/dev/tpmrm0</filename> with <constant>rw</constant> mode to
+        <varname>DeviceAllow=</varname>. See
+        <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        for the details about <varname>DevicePolicy=</varname> or <varname>DeviceAllow=</varname>.</para>
 
         <para>The credential files/IPC sockets must be accessible to the service manager, but don't have to
         be directly accessible to the unit's processes: the credential data is read and copied into separate,

diff --git a/src/core/unit.c b/src/core/unit.c
index 499e9b40edac11e7d562e4e44adb9879e6bcaac7..78a1f72f7fd05746957df0f56c35c7532b7c17f4 100644 (file)
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -4169,6 +4169,16 @@ int unit_patch_contexts(Unit *u) {
                                 if (r < 0)
                                         return r;
                         }
+
+                        /* If there are encrypted credentials we might need to access the TPM. */
+                        ExecLoadCredential *cred;
+                        HASHMAP_FOREACH(cred, ec->load_credentials)
+                                if (cred->encrypted) {
+                                        r = cgroup_add_device_allow(cc, "/dev/tpmrm0", "rw");
+                                        if (r < 0)
+                                                return r;
+                                        break;
+                                }
                 }
         }
 

diff --git a/test/units/testsuite-70.sh b/test/units/testsuite-70.sh
index 589baf370fc1f281e7a2d02f85070149f81d6fd2..54e30642a5a091900da4fcb441c22ed42bc82c92 100755 (executable)
--- a/test/units/testsuite-70.sh
+++ b/test/units/testsuite-70.sh
@@ -208,6 +208,12 @@ else
     echo "/usr/lib/systemd/systemd-pcrphase or PCR sysfs files not found, skipping PCR extension test case"
 fi
 
+# Ensure that sandboxing doesn't stop creds from being accessible
+echo "test" > /tmp/testdata
+systemd-creds encrypt /tmp/testdata /tmp/testdata.encrypted --with-key=tpm2
+systemd-run -p PrivateDevices=yes -p LoadCredentialEncrypted=testdata.encrypted:/tmp/testdata.encrypted --pipe --wait systemd-creds cat testdata.encrypted | cmp - /tmp/testdata
+rm /tmp/testdata
+
 echo OK >/testok
 
 exit 0