ima: re-introduce own integrity cache lockima-next-old

Before IMA appraisal was introduced, IMA was using own integrity cache
lock along with i_mutex. process_measurement and ima_file_free took
the iint->mutex first and then the i_mutex, while setxattr, chmod and
chown took the locks in reverse order. To resolve the potential deadlock,
i_mutex was moved to protect entire IMA functionality and the redundant
iint->mutex was eliminated.

Solution was based on the assumption that filesystem code does not take
i_mutex further. But when file is opened with O_DIRECT flag, direct-io
implementation takes i_mutex and produces deadlock. Furthermore, certain
other filesystem operations, such as llseek, also take i_mutex.

To resolve O_DIRECT related deadlock problem, this patch re-introduces
iint->mutex. But to eliminate the original chmod() related deadlock
problem, this patch eliminates the requirement for chmod hooks to take
the iint->mutex by introducing additional atomic iint->attr_flags to
indicate calling of the hooks. The allowed locking order is to take
the iint->mutex first and then the i_mutex.

Changes in v4:
* adoped to violation detection fixes
* added IMA_UPDATE_XATTR flag to require xattr update on file close

Changes in v3:
* prevent signature removal with new locking
* rename attr_flags to atomic_flags

Changes in v2:
* revert taking the i_mutex in integrity_inode_get() so that iint allocation
  could be done with i_mutex taken
* move taking the i_mutex from appraisal code to the process_measurement()

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@huawei.com>

4 files changed, 72 insertions, 41 deletions

diff --git a/security/integrity/iint.c b/security/integrity/iint.c
index 2de9c820903f1..eb6b0f4602106 100644
--- a/security/integrity/iint.c
+++ b/security/integrity/iint.c
@@ -154,11 +154,13 @@ static void init_once(void *foo)
 	memset(iint, 0, sizeof(*iint));
 	iint->version = 0;
 	iint->flags = 0UL;
+	iint->atomic_flags = 0;
 	iint->ima_file_status = INTEGRITY_UNKNOWN;
 	iint->ima_mmap_status = INTEGRITY_UNKNOWN;
 	iint->ima_bprm_status = INTEGRITY_UNKNOWN;
 	iint->ima_module_status = INTEGRITY_UNKNOWN;
 	iint->evm_status = INTEGRITY_UNKNOWN;
+	mutex_init(&iint->mutex);
 }
 
 static int __init integrity_iintcache_init(void)
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 1873b5536f804..3ac578084a886 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -229,6 +229,7 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
 			status = INTEGRITY_FAIL;
 			break;
 		}
+		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 		if (xattr_len - sizeof(xattr_value->type) - hash_start >=
 				iint->ima_hash->length)
 			/* xattr length may be longer. md5 hash in previous
@@ -247,7 +248,7 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
 		status = INTEGRITY_PASS;
 		break;
 	case EVM_IMA_XATTR_DIGSIG:
-		iint->flags |= IMA_DIGSIG;
+		set_bit(IMA_DIGSIG, &iint->atomic_flags);
 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 					     (const char *)xattr_value, rc,
 					     iint->ima_hash->digest,
@@ -293,14 +294,16 @@ void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 	int rc = 0;
 
 	/* do not collect and update hash for digital signatures */
-	if (iint->flags & IMA_DIGSIG)
+	if (test_bit(IMA_DIGSIG, &iint->atomic_flags))
 		return;
 
 	rc = ima_collect_measurement(iint, file, NULL, NULL);
 	if (rc < 0)
 		return;
 
+	mutex_lock(&file_inode(file)->i_mutex);
 	ima_fix_xattr(dentry, iint);
+	mutex_unlock(&file_inode(file)->i_mutex);
 }
 
 /**
@@ -316,24 +319,21 @@ void ima_inode_post_setattr(struct dentry *dentry)
 {
 	struct inode *inode = d_backing_inode(dentry);
 	struct integrity_iint_cache *iint;
-	int must_appraise, rc;
+	int must_appraise;
 
 	if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode)
 	    || !inode->i_op->removexattr)
 		return;
 
 	must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
+	if (!must_appraise)
+		inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
 	iint = integrity_iint_find(inode);
 	if (iint) {
-		iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
-				 IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
-				 IMA_ACTION_FLAGS);
-		if (must_appraise)
-			iint->flags |= IMA_APPRAISE;
+		set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags);
+		if (!must_appraise)
+			clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 	}
-	if (!must_appraise)
-		rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
-	return;
 }
 
 /*
@@ -362,11 +362,11 @@ static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 	iint = integrity_iint_find(inode);
 	if (!iint)
 		return;
-
-	iint->flags &= ~IMA_DONE_MASK;
+	set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags);
 	if (digsig)
-		iint->flags |= IMA_DIGSIG;
-	return;
+		set_bit(IMA_DIGSIG, &iint->atomic_flags);
+	else
+		clear_bit(IMA_DIGSIG, &iint->atomic_flags);
 }
 
 int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index c21f09bf8b992..6a2c11189a697 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -117,20 +117,23 @@ static void ima_check_last_writer(struct integrity_iint_cache *iint,
 				  struct inode *inode, struct file *file)
 {
 	fmode_t mode = file->f_mode;
+	bool update;
 
 	if (!(mode & FMODE_WRITE))
 		return;
 
-	mutex_lock(&inode->i_mutex);
+	mutex_lock(&iint->mutex);
 	if (atomic_read(&inode->i_writecount) == 1) {
+		update = test_and_clear_bit(IMA_UPDATE_XATTR,
+					    &iint->atomic_flags);
 		if ((iint->version != inode->i_version) ||
 		    (iint->flags & IMA_NEW_FILE)) {
 			iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
-			if (iint->flags & IMA_APPRAISE)
+			if (update)
 				ima_update_xattr(iint, file);
 		}
 	}
-	mutex_unlock(&inode->i_mutex);
+	mutex_unlock(&iint->mutex);
 }
 
 /**
@@ -162,7 +165,7 @@ static int process_measurement(struct file *file, int mask, int function,
 	struct ima_template_desc *template_desc;
 	char *pathbuf = NULL;
 	const char *pathname = NULL;
-	int rc = -ENOMEM, action, must_appraise;
+	int rc = 0, action, must_appraise = 0;
 	struct evm_ima_xattr_data *xattr_value = NULL, **xattr_ptr = NULL;
 	int xattr_len = 0;
 	bool violation_check;
@@ -191,17 +194,31 @@ static int process_measurement(struct file *file, int mask, int function,
 	if (action) {
 		iint = integrity_inode_get(inode);
 		if (!iint)
-			goto out;
+			rc = -ENOMEM;
 	}
 
-	if (violation_check) {
+	if (!rc && violation_check)
 		ima_rdwr_violation_check(file, iint, action & IMA_MEASURE,
 					 &pathbuf, &pathname);
-		if (!action) {
-			rc = 0;
-			goto out_free;
-		}
-	}
+
+	mutex_unlock(&inode->i_mutex);
+
+	if (rc)
+		goto out;
+	if (!action)
+		goto out;
+
+	mutex_lock(&iint->mutex);
+
+	if (test_and_clear_bit(IMA_CHANGE_ATTR, &iint->atomic_flags))
+		/* reset appraisal flags if ima_inode_post_setattr was called */
+		iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED |
+				 IMA_APPRAISE_SUBMASK | IMA_APPRAISED_SUBMASK |
+				 IMA_ACTION_FLAGS);
+
+	if (test_and_clear_bit(IMA_CHANGE_XATTR, &iint->atomic_flags))
+		/* reset all flags if ima_inode_setxattr was called */
+		iint->flags &= ~IMA_DONE_MASK;
 
 	/* Determine if already appraised/measured based on bitmask
 	 * (IMA_MEASURE, IMA_MEASURED, IMA_XXXX_APPRAISE, IMA_XXXX_APPRAISED,
@@ -215,7 +232,7 @@ static int process_measurement(struct file *file, int mask, int function,
 	if (!action) {
 		if (must_appraise)
 			rc = ima_get_cache_status(iint, function);
-		goto out_digsig;
+		goto out_locked;
 	}
 
 	template_desc = ima_template_desc_current();
@@ -227,7 +244,7 @@ static int process_measurement(struct file *file, int mask, int function,
 	if (rc != 0) {
 		if (file->f_flags & O_DIRECT)
 			rc = (iint->flags & IMA_PERMIT_DIRECTIO) ? 0 : -EACCES;
-		goto out_digsig;
+		goto out_locked;
 	}
 
 	if (!pathname)	/* ima_rdwr_violation possibly pre-fetched */
@@ -236,23 +253,28 @@ static int process_measurement(struct file *file, int mask, int function,
 	if (action & IMA_MEASURE)
 		ima_store_measurement(iint, file, pathname,
 				      xattr_value, xattr_len);
-	if (action & IMA_APPRAISE_SUBMASK)
+	if (action & IMA_APPRAISE_SUBMASK) {
+		mutex_lock(&inode->i_mutex);
 		rc = ima_appraise_measurement(function, iint, file, pathname,
 					      xattr_value, xattr_len, opened);
+		mutex_unlock(&inode->i_mutex);
+	}
 	if (action & IMA_AUDIT)
 		ima_audit_measurement(iint, pathname);
-
-out_digsig:
-	if ((mask & MAY_WRITE) && (iint->flags & IMA_DIGSIG))
+out_locked:
+	if ((mask & MAY_WRITE) && test_bit(IMA_DIGSIG, &iint->atomic_flags))
 		rc = -EACCES;
+	mutex_unlock(&iint->mutex);
 	kfree(xattr_value);
-out_free:
+out:
 	if (pathbuf)
 		__putname(pathbuf);
-out:
-	mutex_unlock(&inode->i_mutex);
-	if ((rc && must_appraise) && (ima_appraise & IMA_APPRAISE_ENFORCE))
-		return -EACCES;
+	if (must_appraise) {
+		if (rc && (ima_appraise & IMA_APPRAISE_ENFORCE))
+			return -EACCES;
+		if (file->f_mode & FMODE_WRITE)
+			set_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
+	}
 	return 0;
 }
 
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index 5efe2ecc538d3..37e48e9633db1 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -28,10 +28,9 @@
 
 /* iint cache flags */
 #define IMA_ACTION_FLAGS	0xff000000
-#define IMA_DIGSIG		0x01000000
-#define IMA_DIGSIG_REQUIRED	0x02000000
-#define IMA_PERMIT_DIRECTIO	0x04000000
-#define IMA_NEW_FILE		0x08000000
+#define IMA_DIGSIG_REQUIRED	0x01000000
+#define IMA_PERMIT_DIRECTIO	0x02000000
+#define IMA_NEW_FILE		0x04000000
 
 #define IMA_DO_MASK		(IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \
 				 IMA_APPRAISE_SUBMASK)
@@ -56,6 +55,12 @@
 				 IMA_BPRM_APPRAISED | IMA_MODULE_APPRAISED | \
 				 IMA_FIRMWARE_APPRAISED)
 
+/* iint cache atomic_flags */
+#define IMA_CHANGE_XATTR	0
+#define IMA_UPDATE_XATTR	1
+#define IMA_CHANGE_ATTR		2
+#define IMA_DIGSIG		3
+
 enum evm_ima_xattr_type {
 	IMA_XATTR_DIGEST = 0x01,
 	EVM_XATTR_HMAC,
@@ -103,9 +108,11 @@ struct signature_v2_hdr {
 /* integrity data associated with an inode */
 struct integrity_iint_cache {
 	struct rb_node rb_node;	/* rooted in integrity_iint_tree */
+	struct mutex mutex;	/* protects: version, flags, digest */
 	struct inode *inode;	/* back pointer to inode in question */
 	u64 version;		/* track inode changes */
 	unsigned long flags;
+	unsigned long atomic_flags;
 	enum integrity_status ima_file_status:4;
 	enum integrity_status ima_mmap_status:4;
 	enum integrity_status ima_bprm_status:4;