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, 7 insertions, 2 deletions

diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index 50a8e3365df7..843ae23ba0ac 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -51,10 +51,14 @@
 #define IMA_BPRM_APPRAISED	0x00020000
 #define IMA_READ_APPRAISE	0x00040000
 #define IMA_READ_APPRAISED	0x00080000
+#define IMA_CREDS_APPRAISE	0x00100000
+#define IMA_CREDS_APPRAISED	0x00200000
 #define IMA_APPRAISE_SUBMASK	(IMA_FILE_APPRAISE | IMA_MMAP_APPRAISE | \
-				 IMA_BPRM_APPRAISE | IMA_READ_APPRAISE)
+				 IMA_BPRM_APPRAISE | IMA_READ_APPRAISE | \
+				 IMA_CREDS_APPRAISE)
 #define IMA_APPRAISED_SUBMASK	(IMA_FILE_APPRAISED | IMA_MMAP_APPRAISED | \
-				 IMA_BPRM_APPRAISED | IMA_READ_APPRAISED)
+				 IMA_BPRM_APPRAISED | IMA_READ_APPRAISED | \
+				 IMA_CREDS_APPRAISED)
 
 /* iint cache atomic_flags */
 #define IMA_CHANGE_XATTR	0
@@ -121,6 +125,7 @@ struct integrity_iint_cache {
 	enum integrity_status ima_mmap_status:4;
 	enum integrity_status ima_bprm_status:4;
 	enum integrity_status ima_read_status:4;
+	enum integrity_status ima_creds_status:4;
 	enum integrity_status evm_status:4;
 	struct ima_digest_data *ima_hash;
 };