ima: fallback to using i_version to detect file change

Commit db1d1e8 ("IMA: use vfs_getattr_nosec to get the i_version")
replaced detecting file change based on i_version with
STATX_CHANGE_COOKIE.

On filesystems without STATX_CHANGE_COOKIE enabled, revert back to
detecting file change based on i_version.

On filesystems which do not support either, assume the file changed.

Reported-by: Frederick Lawler <fred@cloudflare.com>
Fixes: db1d1e8 ("IMA: use vfs_getattr_nosec to get the i_version")
Cc: stable@vger.kernel.org
Reviewed-by: Frederick Lawler <fred@cloudflare.com>
Tested-by: Frederick Lawler <fred@cloudflare.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

Author: mimizohar

security/integrity/ima/ima_api.c

@@ -269,15 +269,20 @@ int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
 		goto out;
 
 	/*
-	 * Detecting file change is based on i_version. On filesystems
-	 * which do not support i_version, support was originally limited
-	 * to an initial measurement/appraisal/audit, but was modified to
-	 * assume the file changed.
+	 * Detect file change based on STATX_CHANGE_COOKIE, when supported,
+	 * and fallback to detecting file change based on i_version.
+	 *
+	 * On filesystems which did not support i_version, support was
+	 * originally limited to an initial measurement/appraisal/audit,
+	 * but was later modified to assume the file changed.
 	 */
 	result = vfs_getattr_nosec(&file->f_path, &stat, STATX_CHANGE_COOKIE,
 				   AT_STATX_SYNC_AS_STAT);
 	if (!result && (stat.result_mask & STATX_CHANGE_COOKIE))
 		i_version = stat.change_cookie;
+	else if (IS_I_VERSION(real_inode))
+		i_version = inode_peek_iversion(real_inode);
+
 	hash.hdr.algo = algo;
 	hash.hdr.length = hash_digest_size[algo];
 

security/integrity/ima/ima_main.c

@@ -180,6 +180,29 @@ static void ima_rdwr_violation_check(struct file *file,
 				  "invalid_pcr", "open_writers");
 }
 
+/*
+ * Detect file change based on STATX_CHANGE_COOKIE, when supported, and
+ * fallback to detecting file change based on i_version. On filesystems
+ * which do not support either, assume the file changed.
+ */
+static bool ima_detect_file_change(struct ima_iint_cache *iint,
+				   struct inode *inode, struct file *file)
+{
+	struct kstat stat;
+	int result;
+
+	result = vfs_getattr_nosec(&file->f_path, &stat, STATX_CHANGE_COOKIE,
+				   AT_STATX_SYNC_AS_STAT);
+
+	if (!result && stat.result_mask & STATX_CHANGE_COOKIE)
+		return stat.change_cookie != iint->real_inode.version;
+
+	if (IS_I_VERSION(inode))
+		return !inode_eq_iversion(inode, iint->real_inode.version);
+
+	return true;
+}
+
 static void ima_check_last_writer(struct ima_iint_cache *iint,
 				  struct inode *inode, struct file *file)
 {
@@ -191,18 +214,13 @@ static void ima_check_last_writer(struct ima_iint_cache *iint,
 
 	mutex_lock(&iint->mutex);
 	if (atomic_read(&inode->i_writecount) == 1) {
-		struct kstat stat;
-
 		clear_bit(IMA_EMITTED_OPENWRITERS, &iint->atomic_flags);
 
 		update = test_and_clear_bit(IMA_UPDATE_XATTR,
 					    &iint->atomic_flags);
-		if ((iint->flags & IMA_NEW_FILE) ||
-		    vfs_getattr_nosec(&file->f_path, &stat,
-				      STATX_CHANGE_COOKIE,
-				      AT_STATX_SYNC_AS_STAT) ||
-		    !(stat.result_mask & STATX_CHANGE_COOKIE) ||
-		    stat.change_cookie != iint->real_inode.version) {
+
+		if (iint->flags & IMA_NEW_FILE ||
+		    ima_detect_file_change(iint, inode, file)) {
 			iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
 			iint->measured_pcrs = 0;
 			if (update)