IMA: use vfs_getattr_nosec to get the i_version

IMA currently accesses the i_version out of the inode directly when it
does a measurement. This is fine for most simple filesystems, but can be
problematic with more complex setups (e.g. overlayfs).

Make IMA instead call vfs_getattr_nosec to get this info. This allows
the filesystem to determine whether and how to report the i_version, and
should allow IMA to work properly with a broader class of filesystems in
the future.
Reported-and-Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/ima/ima_api.c

@@ -13,7 +13,6 @@
 #include <linux/fs.h>
 #include <linux/xattr.h>
 #include <linux/evm.h>
-#include <linux/iversion.h>
 #include <linux/fsverity.h>
 
 #include "ima.h"
@@ -246,10 +245,11 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 	struct inode *inode = file_inode(file);
 	const char *filename = file->f_path.dentry->d_name.name;
 	struct ima_max_digest_data hash;
+	struct kstat stat;
 	int result = 0;
 	int length;
 	void *tmpbuf;
-	u64 i_version;
+	u64 i_version = 0;
 
 	/*
 	 * Always collect the modsig, because IMA might have already collected
@@ -268,7 +268,10 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 	 * to an initial measurement/appraisal/audit, but was modified to
 	 * assume the file changed.
 	 */
-	i_version = inode_query_iversion(inode);
+	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;
 	hash.hdr.algo = algo;
 	hash.hdr.length = hash_digest_size[algo];
 

security/integrity/ima/ima_main.c

@@ -24,7 +24,6 @@
 #include <linux/slab.h>
 #include <linux/xattr.h>
 #include <linux/ima.h>
-#include <linux/iversion.h>
 #include <linux/fs.h>
 
 #include "ima.h"
@@ -164,11 +163,16 @@ static void ima_check_last_writer(struct integrity_iint_cache *iint,
 
 	mutex_lock(&iint->mutex);
 	if (atomic_read(&inode->i_writecount) == 1) {
+		struct kstat stat;
+
 		update = test_and_clear_bit(IMA_UPDATE_XATTR,
 					    &iint->atomic_flags);
-		if (!IS_I_VERSION(inode) ||
-		    !inode_eq_iversion(inode, iint->version) ||
-		    (iint->flags & IMA_NEW_FILE)) {
+		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->version) {
 			iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
 			iint->measured_pcrs = 0;
 			if (update)