ima: Store the measurement again when appraising a modsig

If the IMA template contains the "modsig" or "d-modsig" field, then the
modsig should be added to the measurement list when the file is appraised.

And that is what normally happens, but if a measurement rule caused a file
containing a modsig to be measured before a different rule causes it to be
appraised, the resulting measurement entry will not contain the modsig
because it is only fetched during appraisal. When the appraisal rule
triggers, it won't store a new measurement containing the modsig because
the file was already measured.

We need to detect that situation and store an additional measurement with
the modsig. This is done by adding an IMA_MEASURE action flag if we read a
modsig and the IMA template contains a modsig field.

Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

1 files changed, 15 insertions, 4 deletions

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index ca930e2ebc2c..65224474675b 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -219,6 +219,14 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 		char digest[IMA_MAX_DIGEST_SIZE];
 	} hash;
 
+	/*
+	 * Always collect the modsig, because IMA might have already collected
+	 * the file digest without collecting the modsig in a previous
+	 * measurement rule.
+	 */
+	if (modsig)
+		ima_collect_modsig(modsig, buf, size);
+
 	if (iint->flags & IMA_COLLECTED)
 		goto out;
 
@@ -252,9 +260,6 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 	memcpy(iint->ima_hash, &hash, length);
 	iint->version = i_version;
 
-	if (modsig)
-		ima_collect_modsig(modsig, buf, size);
-
 	/* Possibly temporary failure due to type of read (eg. O_DIRECT) */
 	if (!result)
 		iint->flags |= IMA_COLLECTED;
@@ -304,7 +309,13 @@ void ima_store_measurement(struct integrity_iint_cache *iint,
 					     .modsig = modsig };
 	int violation = 0;
 
-	if (iint->measured_pcrs & (0x1 << pcr))
+	/*
+	 * We still need to store the measurement in the case of MODSIG because
+	 * we only have its contents to put in the list at the time of
+	 * appraisal, but a file measurement from earlier might already exist in
+	 * the measurement list.
+	 */
+	if (iint->measured_pcrs & (0x1 << pcr) && !modsig)
 		return;
 
 	result = ima_alloc_init_template(&event_data, &entry, template_desc);