IMA: Support using new creds in appraisal policy

The existing BPRM_CHECK functionality in IMA validates against the
credentials of the existing process, not any new credentials that the
child process may transition to. Add an additional CREDS_CHECK target
and refactor IMA to pass the appropriate creds structure. In
ima_bprm_check(), check with both the existing process credentials and
the credentials that will be committed when the new process is started.
This will not change behaviour unless the system policy is extended to
include CREDS_CHECK targets - BPRM_CHECK will continue to check the same
credentials that it did previously.

After this patch, an IMA policy rule along the lines of:

measure func=CREDS_CHECK subj_type=unconfined_t

will trigger if a process is executed and runs as unconfined_t, ignoring
the context of the parent process. This is in contrast to:

measure func=BPRM_CHECK subj_type=unconfined_t

which will trigger if the process that calls exec() is already executing
in unconfined_t, ignoring the context that the child process executes
into.

Signed-off-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

Changelog:
- initialize ima_creds_status

1 files changed, 32 insertions, 10 deletions

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 2cfb0c714967..a5d225ffc388 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -167,8 +167,9 @@ void ima_file_free(struct file *file)
 	ima_check_last_writer(iint, inode, file);
 }
 
-static int process_measurement(struct file *file, char *buf, loff_t size,
-			       int mask, enum ima_hooks func, int opened)
+static int process_measurement(struct file *file, const struct cred *cred,
+			       u32 secid, char *buf, loff_t size, int mask,
+			       enum ima_hooks func, int opened)
 {
 	struct inode *inode = file_inode(file);
 	struct integrity_iint_cache *iint = NULL;
@@ -190,7 +191,7 @@ static int process_measurement(struct file *file, char *buf, loff_t size,
 	 * bitmask based on the appraise/audit/measurement policy.
 	 * Included is the appraise submask.
 	 */
-	action = ima_get_action(inode, mask, func, &pcr);
+	action = ima_get_action(inode, cred, secid, mask, func, &pcr);
 	violation_check = ((func == FILE_CHECK || func == MMAP_CHECK) &&
 			   (ima_policy_flag & IMA_MEASURE));
 	if (!action && !violation_check)
@@ -324,9 +325,14 @@ out:
  */
 int ima_file_mmap(struct file *file, unsigned long prot)
 {
-	if (file && (prot & PROT_EXEC))
-		return process_measurement(file, NULL, 0, MAY_EXEC,
-					   MMAP_CHECK, 0);
+	u32 secid;
+
+	if (file && (prot & PROT_EXEC)) {
+		security_task_getsecid(current, &secid);
+		return process_measurement(file, current_cred(), secid, NULL,
+					   0, MAY_EXEC, MMAP_CHECK, 0);
+	}
+
 	return 0;
 }
 
@@ -345,8 +351,18 @@ int ima_file_mmap(struct file *file, unsigned long prot)
  */
 int ima_bprm_check(struct linux_binprm *bprm)
 {
-	return process_measurement(bprm->file, NULL, 0, MAY_EXEC,
-				   BPRM_CHECK, 0);
+	int ret;
+	u32 secid;
+
+	security_task_getsecid(current, &secid);
+	ret = process_measurement(bprm->file, current_cred(), secid, NULL, 0,
+				  MAY_EXEC, BPRM_CHECK, 0);
+	if (ret)
+		return ret;
+
+	security_cred_getsecid(bprm->cred, &secid);
+	return process_measurement(bprm->file, bprm->cred, secid, NULL, 0,
+				   MAY_EXEC, CREDS_CHECK, 0);
 }
 
 /**
@@ -361,7 +377,10 @@ int ima_bprm_check(struct linux_binprm *bprm)
  */
 int ima_file_check(struct file *file, int mask, int opened)
 {
-	return process_measurement(file, NULL, 0,
+	u32 secid;
+
+	security_task_getsecid(current, &secid);
+	return process_measurement(file, current_cred(), secid, NULL, 0,
 				   mask & (MAY_READ | MAY_WRITE | MAY_EXEC |
 					   MAY_APPEND), FILE_CHECK, opened);
 }
@@ -440,6 +459,7 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
 		       enum kernel_read_file_id read_id)
 {
 	enum ima_hooks func;
+	u32 secid;
 
 	if (!file && read_id == READING_FIRMWARE) {
 		if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
@@ -462,7 +482,9 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
 	}
 
 	func = read_idmap[read_id] ?: FILE_CHECK;
-	return process_measurement(file, buf, size, MAY_READ, func, 0);
+	security_task_getsecid(current, &secid);
+	return process_measurement(file, current_cred(), secid, buf, size,
+				   MAY_READ, func, 0);
 }
 
 static int __init init_ima(void)