diff mbox

[V5,2/2] IMA: Support using new creds in appraisal policy

Message ID 20180105211536.11611-2-mjg59@google.com (mailing list archive)
State Superseded
Headers show

Commit Message

Jann Horn via Selinux Jan. 5, 2018, 9:15 p.m. UTC 
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.

Signed-off-by: Matthew Garrett <mjg59@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Eric Paris <eparis@parisplace.org>
Cc: selinux@tycho.nsa.gov
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: linux-security-module@vger.kernel.org
Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Dmitry Kasatkin <dmitry.kasatkin@gmail.com>
Cc: linux-integrity@vger.kernel.org
---
 Documentation/ABI/testing/ima_policy  |  2 +-
 security/integrity/iint.c             |  1 +
 security/integrity/ima/ima.h          |  9 ++++----
 security/integrity/ima/ima_api.c      |  9 +++++---
 security/integrity/ima/ima_appraise.c | 13 ++++++++++-
 security/integrity/ima/ima_main.c     | 42 ++++++++++++++++++++++++++---------
 security/integrity/ima/ima_policy.c   | 23 ++++++++++++-------
 security/integrity/integrity.h        |  9 ++++++--
 8 files changed, 79 insertions(+), 29 deletions(-)

Comments

Mimi Zohar Jan. 8, 2018, 12:18 p.m. UTC | #1 
On Fri, 2018-01-05 at 13:15 -0800, Matthew Garrett wrote:
> 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.

Refactoring IMA to pass the creds structure all the way down is a
generic solution, but if the CREDS_CHECK rule is only being called
from ima_bprm_check(), "container_of" the bprm->file returns a pointer
to the bprm structure.  Perhaps you could limit the amount of
refactoring needed based on the func.

I would prefer new arguments be added to process_measurement() only as
a last resort.

Could you include in the patch description a simple method for testing
this change?

thanks,

Mimi
Jann Horn via Selinux Jan. 8, 2018, 7:45 p.m. UTC | #2 
On Mon, Jan 8, 2018 at 4:18 AM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> On Fri, 2018-01-05 at 13:15 -0800, Matthew Garrett wrote:
>> 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.
>
> Refactoring IMA to pass the creds structure all the way down is a
> generic solution, but if the CREDS_CHECK rule is only being called
> from ima_bprm_check(), "container_of" the bprm->file returns a pointer
> to the bprm structure.  Perhaps you could limit the amount of
> refactoring needed based on the func.

Hm. This would avoid adding an argument to process_measurement(), but
we'd still need to pass additional information down through
ima_get_action() in order to get the creds and secid right. It feels a
little ugly to have process_measurement() recreate information rather
than having the caller pass it in, but I'm not going to object.

> Could you include in the patch description a simple method for testing
> this change?

Certainly.
Mimi Zohar Jan. 8, 2018, 7:55 p.m. UTC | #3 
On Mon, 2018-01-08 at 11:45 -0800, Matthew Garrett wrote:
> On Mon, Jan 8, 2018 at 4:18 AM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> > On Fri, 2018-01-05 at 13:15 -0800, Matthew Garrett wrote:
> >> 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.
> >
> > Refactoring IMA to pass the creds structure all the way down is a
> > generic solution, but if the CREDS_CHECK rule is only being called
> > from ima_bprm_check(), "container_of" the bprm->file returns a pointer
> > to the bprm structure.  Perhaps you could limit the amount of
> > refactoring needed based on the func.
> 
> Hm. This would avoid adding an argument to process_measurement(), but
> we'd still need to pass additional information down through
> ima_get_action() in order to get the creds and secid right. It feels a
> little ugly to have process_measurement() recreate information rather
> than having the caller pass it in, but I'm not going to object.

Agreed.  Initially, I was thinking that only ima_match_rules() would
use container_of, but the very first thing process_measurement() does
is get the inode from the file.  Everything afterwards passes the
inode.

> > Could you include in the patch description a simple method for testing
> > this change?
> 
> Certainly.

Thanks!

Mimi
diff mbox

Patch

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index e76432b9954d..5dc9eed035fb 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -25,7 +25,7 @@  Description:
 				 [obj_user=] [obj_role=] [obj_type=]]
 			option:	[[appraise_type=]] [permit_directio]
 
-		base: 	func:= [BPRM_CHECK][MMAP_CHECK][FILE_CHECK][MODULE_CHECK]
+		base: 	func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
 				[FIRMWARE_CHECK]
 				[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
 			mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
diff --git a/security/integrity/iint.c b/security/integrity/iint.c
index c84e05866052..62846e331a8b 100644
--- a/security/integrity/iint.c
+++ b/security/integrity/iint.c
@@ -78,6 +78,7 @@  static void iint_free(struct integrity_iint_cache *iint)
 	iint->ima_mmap_status = INTEGRITY_UNKNOWN;
 	iint->ima_bprm_status = INTEGRITY_UNKNOWN;
 	iint->ima_read_status = INTEGRITY_UNKNOWN;
+	iint->ima_creds_status = INTEGRITY_UNKNOWN;
 	iint->evm_status = INTEGRITY_UNKNOWN;
 	iint->measured_pcrs = 0;
 	kmem_cache_free(iint_cache, iint);
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index d52b487ad259..35fe91aa1fc9 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -177,6 +177,7 @@  static inline unsigned long ima_hash_key(u8 *digest)
 	hook(FILE_CHECK)		\
 	hook(MMAP_CHECK)		\
 	hook(BPRM_CHECK)		\
+	hook(CREDS_CHECK)		\
 	hook(POST_SETATTR)		\
 	hook(MODULE_CHECK)		\
 	hook(FIRMWARE_CHECK)		\
@@ -191,8 +192,8 @@  enum ima_hooks {
 };
 
 /* LIM API function definitions */
-int ima_get_action(struct inode *inode, int mask,
-		   enum ima_hooks func, int *pcr);
+int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
+		   int mask, enum ima_hooks func, int *pcr);
 int ima_must_measure(struct inode *inode, int mask, enum ima_hooks func);
 int ima_collect_measurement(struct integrity_iint_cache *iint,
 			    struct file *file, void *buf, loff_t size,
@@ -212,8 +213,8 @@  void ima_free_template_entry(struct ima_template_entry *entry);
 const char *ima_d_path(const struct path *path, char **pathbuf, char *filename);
 
 /* IMA policy related functions */
-int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask,
-		     int flags, int *pcr);
+int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
+		     enum ima_hooks func, int mask, int flags, int *pcr);
 void ima_init_policy(void);
 void ima_update_policy(void);
 void ima_update_policy_flag(void);
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index c7e8db0ea4c0..09a8da070162 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -157,6 +157,8 @@  void ima_add_violation(struct file *file, const unsigned char *filename,
 /**
  * ima_get_action - appraise & measure decision based on policy.
  * @inode: pointer to inode to measure
+ * @cred: pointer to credentials structure to validate
+ * @secid: secid of the task being validated
  * @mask: contains the permission mask (MAY_READ, MAY_WRITE, MAY_EXEC,
  *        MAY_APPEND)
  * @func: caller identifier
@@ -165,20 +167,21 @@  void ima_add_violation(struct file *file, const unsigned char *filename,
  * The policy is defined in terms of keypairs:
  *		subj=, obj=, type=, func=, mask=, fsmagic=
  *	subj,obj, and type: are LSM specific.
- *	func: FILE_CHECK | BPRM_CHECK | MMAP_CHECK | MODULE_CHECK
+ *	func: FILE_CHECK | BPRM_CHECK | CREDS_CHECK | MMAP_CHECK | MODULE_CHECK
  *	mask: contains the permission mask
  *	fsmagic: hex value
  *
  * Returns IMA_MEASURE, IMA_APPRAISE mask.
  *
  */
-int ima_get_action(struct inode *inode, int mask, enum ima_hooks func, int *pcr)
+int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
+		   int mask, enum ima_hooks func, int *pcr)
 {
 	int flags = IMA_MEASURE | IMA_AUDIT | IMA_APPRAISE;
 
 	flags &= ima_policy_flag;
 
-	return ima_match_policy(inode, func, mask, flags, pcr);
+	return ima_match_policy(inode, cred, secid, func, mask, flags, pcr);
 }
 
 /*
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 65fbcf3c32c7..23453a5a86ac 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -50,10 +50,14 @@  bool is_ima_appraise_enabled(void)
  */
 int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
 {
+	u32 secid;
+
 	if (!ima_appraise)
 		return 0;
 
-	return ima_match_policy(inode, func, mask, IMA_APPRAISE, NULL);
+	security_task_getsecid(current, &secid);
+	return ima_match_policy(inode, current_cred(), secid, func, mask,
+				IMA_APPRAISE, NULL);
 }
 
 static int ima_fix_xattr(struct dentry *dentry,
@@ -86,6 +90,8 @@  enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
 		return iint->ima_mmap_status;
 	case BPRM_CHECK:
 		return iint->ima_bprm_status;
+	case CREDS_CHECK:
+		return iint->ima_creds_status;
 	case FILE_CHECK:
 	case POST_SETATTR:
 		return iint->ima_file_status;
@@ -106,6 +112,8 @@  static void ima_set_cache_status(struct integrity_iint_cache *iint,
 	case BPRM_CHECK:
 		iint->ima_bprm_status = status;
 		break;
+	case CREDS_CHECK:
+		iint->ima_creds_status = status;
 	case FILE_CHECK:
 	case POST_SETATTR:
 		iint->ima_file_status = status;
@@ -127,6 +135,9 @@  static void ima_cache_flags(struct integrity_iint_cache *iint,
 	case BPRM_CHECK:
 		iint->flags |= (IMA_BPRM_APPRAISED | IMA_APPRAISED);
 		break;
+	case CREDS_CHECK:
+		iint->flags |= (IMA_CREDS_APPRAISED | IMA_APPRAISED);
+		break;
 	case FILE_CHECK:
 	case POST_SETATTR:
 		iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 770654694efc..7ddab02ddd68 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -159,8 +159,9 @@  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;
@@ -182,7 +183,7 @@  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)
@@ -284,9 +285,14 @@  static int process_measurement(struct file *file, char *buf, loff_t size,
  */
 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;
 }
 
@@ -305,8 +311,18 @@  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);
 }
 
 /**
@@ -321,7 +337,10 @@  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);
 }
@@ -398,6 +417,7 @@  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) &&
@@ -420,7 +440,9 @@  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)
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index ee4613fa5840..4321b3bb61ef 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -241,16 +241,17 @@  static void ima_lsm_update_rules(void)
  * ima_match_rules - determine whether an inode matches the measure rule.
  * @rule: a pointer to a rule
  * @inode: a pointer to an inode
+ * @cred: a pointer to a credentials structure for user validation
+ * @secid: the secid of the task to be validated
  * @func: LIM hook identifier
  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
  *
  * Returns true on rule match, false on failure.
  */
 static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
+			    const struct cred *cred, u32 secid,
 			    enum ima_hooks func, int mask)
 {
-	struct task_struct *tsk = current;
-	const struct cred *cred = current_cred();
 	int i;
 
 	if ((rule->flags & IMA_FUNC) &&
@@ -285,7 +286,7 @@  static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
 		return false;
 	for (i = 0; i < MAX_LSM_RULES; i++) {
 		int rc = 0;
-		u32 osid, sid;
+		u32 osid;
 		int retried = 0;
 
 		if (!rule->lsm[i].rule)
@@ -305,8 +306,7 @@  static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
 		case LSM_SUBJ_USER:
 		case LSM_SUBJ_ROLE:
 		case LSM_SUBJ_TYPE:
-			security_task_getsecid(tsk, &sid);
-			rc = security_filter_rule_match(sid,
+			rc = security_filter_rule_match(secid,
 							rule->lsm[i].type,
 							Audit_equal,
 							rule->lsm[i].rule,
@@ -339,6 +339,8 @@  static int get_subaction(struct ima_rule_entry *rule, enum ima_hooks func)
 		return IMA_MMAP_APPRAISE;
 	case BPRM_CHECK:
 		return IMA_BPRM_APPRAISE;
+	case CREDS_CHECK:
+		return IMA_CREDS_APPRAISE;
 	case FILE_CHECK:
 	case POST_SETATTR:
 		return IMA_FILE_APPRAISE;
@@ -351,6 +353,9 @@  static int get_subaction(struct ima_rule_entry *rule, enum ima_hooks func)
 /**
  * ima_match_policy - decision based on LSM and other conditions
  * @inode: pointer to an inode for which the policy decision is being made
+ * @cred: pointer to a credentials structure for which the policy decision is
+ *        being made
+ * @secid: LSM secid of the task to be validated
  * @func: IMA hook identifier
  * @mask: requested action (MAY_READ | MAY_WRITE | MAY_APPEND | MAY_EXEC)
  * @pcr: set the pcr to extend
@@ -362,8 +367,8 @@  static int get_subaction(struct ima_rule_entry *rule, enum ima_hooks func)
  * list when walking it.  Reads are many orders of magnitude more numerous
  * than writes so ima_match_policy() is classical RCU candidate.
  */
-int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask,
-		     int flags, int *pcr)
+int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
+		     enum ima_hooks func, int mask, int flags, int *pcr)
 {
 	struct ima_rule_entry *entry;
 	int action = 0, actmask = flags | (flags << 1);
@@ -374,7 +379,7 @@  int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask,
 		if (!(entry->action & actmask))
 			continue;
 
-		if (!ima_match_rules(entry, inode, func, mask))
+		if (!ima_match_rules(entry, inode, cred, secid, func, mask))
 			continue;
 
 		action |= entry->flags & IMA_ACTION_FLAGS;
@@ -691,6 +696,8 @@  static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
 				entry->func = MMAP_CHECK;
 			else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
 				entry->func = BPRM_CHECK;
+			else if (strcmp(args[0].from, "CREDS_CHECK") == 0)
+				entry->func = CREDS_CHECK;
 			else if (strcmp(args[0].from, "KEXEC_KERNEL_CHECK") ==
 				 0)
 				entry->func = KEXEC_KERNEL_CHECK;
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index e1bf040fb110..d70fd875d62f 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -48,10 +48,14 @@ 
 #define IMA_BPRM_APPRAISED	0x00002000
 #define IMA_READ_APPRAISE	0x00004000
 #define IMA_READ_APPRAISED	0x00008000
+#define IMA_CREDS_APPRAISE	0x00010000
+#define IMA_CREDS_APPRAISED	0x00020000
 #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)
 
 enum evm_ima_xattr_type {
 	IMA_XATTR_DIGEST = 0x01,
@@ -108,6 +112,7 @@  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;
 };