ima: Move file-change detection variables into new structure

Move all the variables used for file change detection into a structure
that can be used by IMA and EVM. Implement an inline function for storing
the identification of an inode and one for detecting changes to an inode
based on this new structure.

Co-developed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

Author: stefanberger

include/linux/integrity.h

@@ -8,6 +8,7 @@
 #define _LINUX_INTEGRITY_H
 
 #include <linux/fs.h>
+#include <linux/iversion.h>
 
 enum integrity_status {
 	INTEGRITY_PASS = 0,
@@ -28,4 +29,37 @@ static inline void integrity_load_keys(void)
 }
 #endif /* CONFIG_INTEGRITY */
 
+/* An inode's attributes for detection of changes */
+struct integrity_inode_attributes {
+	u64 version;		/* track inode changes */
+	unsigned long ino;
+	dev_t dev;
+};
+
+/*
+ * On stacked filesystems the i_version alone is not enough to detect file data
+ * or metadata change. Additional metadata is required.
+ */
+static inline void
+integrity_inode_attrs_store(struct integrity_inode_attributes *attrs,
+			    u64 i_version, const struct inode *inode)
+{
+	attrs->version = i_version;
+	attrs->dev = inode->i_sb->s_dev;
+	attrs->ino = inode->i_ino;
+}
+
+/*
+ * On stacked filesystems detect whether the inode or its content has changed.
+ */
+static inline bool
+integrity_inode_attrs_changed(const struct integrity_inode_attributes *attrs,
+			      const struct inode *inode)
+{
+	return (inode->i_sb->s_dev != attrs->dev ||
+		inode->i_ino != attrs->ino ||
+		!inode_eq_iversion(inode, attrs->version));
+}
+
+
 #endif /* _LINUX_INTEGRITY_H */

security/integrity/ima/ima.h

@@ -175,12 +175,10 @@ struct ima_kexec_hdr {
 /* IMA integrity metadata associated with an inode */
 struct ima_iint_cache {
 	struct mutex mutex;	/* protects: version, flags, digest */
-	u64 version;		/* track inode changes */
+	struct integrity_inode_attributes real_inode;
 	unsigned long flags;
 	unsigned long measured_pcrs;
 	unsigned long atomic_flags;
-	unsigned long real_ino;
-	dev_t real_dev;
 	enum integrity_status ima_file_status:4;
 	enum integrity_status ima_mmap_status:4;
 	enum integrity_status ima_bprm_status:4;

security/integrity/ima/ima_api.c

@@ -305,11 +305,11 @@ int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
 
 	iint->ima_hash = tmpbuf;
 	memcpy(iint->ima_hash, &hash, length);
-	iint->version = i_version;
-	if (real_inode != inode) {
-		iint->real_ino = real_inode->i_ino;
-		iint->real_dev = real_inode->i_sb->s_dev;
-	}
+	if (real_inode == inode)
+		iint->real_inode.version = i_version;
+	else
+		integrity_inode_attrs_store(&iint->real_inode, i_version,
+					    real_inode);
 
 	/* Possibly temporary failure due to type of read (eg. O_DIRECT) */
 	if (!result)

security/integrity/ima/ima_iint.c

@@ -59,7 +59,7 @@ static void ima_iint_init_always(struct ima_iint_cache *iint,
 				 struct inode *inode)
 {
 	iint->ima_hash = NULL;
-	iint->version = 0;
+	iint->real_inode.version = 0;
 	iint->flags = 0UL;
 	iint->atomic_flags = 0UL;
 	iint->ima_file_status = INTEGRITY_UNKNOWN;

security/integrity/ima/ima_main.c

@@ -173,7 +173,7 @@ static void ima_check_last_writer(struct ima_iint_cache *iint,
 				      STATX_CHANGE_COOKIE,
 				      AT_STATX_SYNC_AS_STAT) ||
 		    !(stat.result_mask & STATX_CHANGE_COOKIE) ||
-		    stat.change_cookie != iint->version) {
+		    stat.change_cookie != iint->real_inode.version) {
 			iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
 			iint->measured_pcrs = 0;
 			if (update)
@@ -292,9 +292,8 @@ static int process_measurement(struct file *file, const struct cred *cred,
 	if (real_inode != inode &&
 	    (action & IMA_DO_MASK) && (iint->flags & IMA_DONE_MASK)) {
 		if (!IS_I_VERSION(real_inode) ||
-		    real_inode->i_sb->s_dev != iint->real_dev ||
-		    real_inode->i_ino != iint->real_ino ||
-		    !inode_eq_iversion(real_inode, iint->version)) {
+		    integrity_inode_attrs_changed(&iint->real_inode,
+						  real_inode)) {
 			iint->flags &= ~IMA_DONE_MASK;
 			iint->measured_pcrs = 0;
 		}