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core: imply DeviceAllow=/dev/tpmrm0 with LoadCredentialEncrypted

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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
This commit is contained in:
Luca Boccassi 2023-02-08 00:25:00 +00:00 committed by Luca Boccassi
parent b0fc23fae5
commit 398dc7d39b
3 changed files with 23 additions and 1 deletions
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8
man/systemd.exec.xml
View file

@ -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,

10
src/core/unit.c
View file

@ -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;
}
}
}

6
test/units/testsuite-70.sh
View file

@ -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